Session Q1: Poster Session III (4:00 pm - 6:00 pm)

Energies, radiative rates and Auger branching ratios of core-excited resonances for B-like isoelectronic sequence

The relativistic energies, fine-structures, radiative rates, and Auger branching ratios of the core-excited $1s2p^4$ states for B-like isoelectronic sequences are studied using the saddle-point variation method and saddle-point complex-rotation method. Large-scale wavefunctions are used to obtain reliable results. Relativistic corrections and mass polarization effects are taken into account with first-order perturbation theory. The radiative rates of these states are reported and compared with available theoretical and experimental results. The radiative and Auger transition rates regularly change along the Boron isoelectronic sequence has been investigated. The Auger branching ratios of these resonances are discussed using spin-alignment-dependent theory. Calculated Auger channel energies and branching ratios are used to identify high resolution Auger spectrum in the collision experiments. Several unidentified experimental Auger lines are assigned. It is found that Auger decay of the five-electron core-excited states give significant contributions to the experimental Auger spectrum.   

Hyperfine Structure in the $^{87}$Rb$_{2}$ $1_{g}$ State Below $5^{2}S+5^{2}P_{1/2}$

Hyperfine structure in the Rb$_{2}$ $1_{g} P_{1/2}$ state was observed in photoassociation from cold atoms some time ago, but only partially analyzed. Our Hamiltonian includes the vibrational energy, $G(v)$, rotational energy, $B(v)$, hyperfine interaction, $A(v)\iota$, and off-diagonal elements $F_{\pm}\cdot I_{mp}$. $F$ ranges from 1 to 6, $\iota$ from $-I$ to $I$, where $I$=3. The data scans were precisely calibrated by simultaneously etalon scans. For the 22 vibrational levels (over a range of 50) for which there is precise data, $A(v)$ varies from 2.97$\times 10^{-2}$ cm$^{-1}$ to 3.15 $\times 10^{-2}$ cm$^{-1}$. The $G(v)$ and $B(v)$ values allow us to construct a potential down to 32 cm$^{-1}$ below the dissociation limit.   

Molecular Ion Spectroscopy

We discuss our efforts to perform high-resolution spectroscopy of the BaCl$^+$ ion, an exciting candidate for ultracold molecular ion studies. This work details our search for a predicted predissociation channel between the first-excited $B^1\Sigma$ and $A^1\Pi$ states. It is expected that the rovibrational resolution afforded by predissociation spectroscopy will allow us to efficiently measure molecular-ion rovibrational temperatures. This is a crucial step in confirming our method to produce ultracold molecular ions via sympathetic collisions with a $^{40}$Ca MOT. To observe the predissociation of trapped BaCl$^+$, we detect slight increases in fragment Ba$^+$ with a novel time-of-flight device using radial extraction from a linear quadrupole trap.   

Photoexcitation of high-$n$, $n\sim $ 300, Rydberg states in the presence of an rf driving field near the final Kepler frequency

The photoexcitation of very-high-$n$, $n\sim $ 300, potassium Rydberg atoms in the presence of an rf driving field at, or near, the Kepler frequency of the final state is examined and allows the realization of quantum-optical protocols in truly mesoscopic atoms. When directly exciting 4s $\to n$p transitions using a uv laser, application of the drive field leads to the appearance of new features in the excitation spectrum that lie approximately midway between the $n$p states. Whereas the size of these features increases with increasing drive field amplitude their positions remain largely unchanged. As the rf frequency is detuned from resonance, the features split, the separation of the components being equal to twice the detuning. The new features are attributed to multiphoton transitions to final $n$s and $n$d states that involve the absorption or emission of rf photons. Measurements further suggest that while the electron motion in the product states is locked to the drive field this results from post-excitation interactions with the field rather than the excitation process \textit{per se}. The results are analyzed using Floquet theory.   

Transition Probabilities for Neutral Cerium from Boltzmann Analysis of Fourier Transform Spectra

The recent availability of a large set of absolute transition probabilities for neutral cerium (Lawler \textit{et. al}., J. Phys. B \textbf{43}, 85701 (2010)) makes it possible to investigate the relative populations of the upper levels of these lines in radiometrically-calibrated spectra. In cases where these populations can be characterized by a single effective Boltzmann temperature, applying this temperature enables one to determine additional absolute transition probabilities for observable decay branches of nearby levels. While not as accurate as measurements based on branching fractions and lifetimes, the method can be applied to levels whose lifetimes are not known and does not require accounting for all of the branches. We are analyzing Fourier Transform spectra from NIST and from the National Solar Observatory data archive at Kitt Peak via this technique, seeking to increase the set of known transition probabilities for Ce I by a factor of 2-3. A summary of results obtained to date will be presented.   

Ag-Pb Interaction and Enhanced Fluorescence Emission of Pb$^{2+}$ in Lead Borate Glasses

We carried out Pb$^{2+}$ fluorescence measurements in lead borate glasses and studied the effect of adding Ag into the base glass. Lead borate glasses containing Ag (0 and 3 mol{\%}) were prepared by the usual melt quench method. The prepared glasses were then annealed near the glass transition temperature (400 $^{\circ}$C) at 5, 10, 20 and 30h. Fluorescence spectra of all these samples were obtained using different excitation wavelengths. In general, Pb$^{2+}$ monomers are expected to have emission at wavelength less than 400nm. However, no emission in this region was observed due to the base glass absorption. The emission observed at 450nm is attributed to $^{3}$P$_{1} \to ^{1}$S$_{0}$ transition of Pb$^{2+}$ ions in dimer centers. Addition of Ag enhances the Pb$^{2+}$ luminescence intensity at 450 nm which also shows an increase with the annealing time. The possible mechanisms for the fluorescence enhancement in the present glass could be the energy transfer from isolated Ag particles and local field effects due to the difference between the dielectric functions of the glass matrix and the silver particles.   

Spectroscopic investigation of the $A$ and 3 $^{1}\Sigma ^{+}$ states of $^{39}$K$^{85}$Rb

We have explored the absorption spectra of ultracold $^{39}$K$^{85}$Rb molecules in the region 11,000-12,000 cm$^{-1}$ above the ground state dissociation limit, formed by radiative decay following photoassociation(PA) to either the 3(0$^{+})$ or the 3(0$^{-})$ state. Recently we have reported that molecules formed by using the 3(0$^{-})$ PA level are not excited to the $A$ and 3 $^{1}\Sigma ^{+}$ states, but rather the 1 $^{1}\Pi $, 2 $^{3}\Sigma ^{+}$, and $b \quad ^{3}\Pi $ states. However, we have observed high vibrational levels of these $^{1}\Sigma ^{+ }$states by using the 3(0$^{+})$ level for PA. The absence of the $^{1}\Sigma ^{+}$ states in the spectra from levels formed by the 3(0$^{-})$ PA level has been explained by considering Hund's case (c) selection rules and the transition dipole moment calculations by Kotochigova \textit{et al}.[1] between the upper excited $A$ $^{1}\Sigma ^{+}$(2(0$^{+}))$ state and the three $\Omega $ components at the ground state dissociation limit. Unexpectedly, many high vibrational levels(v$\prime $=26-52) of the 3 $^{1}\Sigma ^{+}$ state, with a small transition dipole moment from the 1(0$^{+})$ state[1], have also been observed. The observed energies of the v$\prime $=26-44 levels match well with those observed from molecular beam experiments. Thus we have fully analyzed the $^{39}$K$^{85}$Rb electronic states in the entire region 11,000-12,000 cm$^{-1}$ above the ground state dissociation limit. \\[4pt] [1]. S. Kotochigova, E. Tiesinga, and P. S. Julienne, Phys. Rev. A \textbf{68}, 022501 (2003). This work is supported by NSF and AFOSR.   

X-ray diffraction assisted spectroscopy of Rydberg states

X-ray diffraction combined with conventional spectroscopy could provide a powerful means to characterize excited atoms and molecules. We demonstrate theoretically how x-ray diffraction from laser excited atoms can be used to determine electronic structure, including angular momentum composition, principal quantum numbers and configuration (channel populations). A theoretical formalism appropriate for highly excited atoms, and easily extended to molecules, is presented together with numerical results for Xe and H atoms.   

\textit{Ab Initio} Study of High-Lying Doubly Excited States of Helium in Static Electric Fields: Complex-Scaling Generalized Pseudospectral Method in Hyperspherical Coordinates

We present a new complex-scaling (CS) generalized pseudospectral (GPS) method in hyperspherical coordinates (HSC) for \textit{ab initio} and accurate treatment of the resonance energies and autoionization widths of two-electron atomic systems in the presence of strong dc electric field. The GPS method allows non-uniform and optimal spatial discretization of the two-electron Hamiltonian in HSC with the use of only a modest number of grid points. The procedure is applied for the first precision calculation of the energies and autoionization widths for the high-lying $^{1}$S$^{e}$, $^{1}$P$^{o}$, $^{1}$D$^{e}$ and $^{1}$F$^{o}$ (n=10 to 20) doubly-excited resonance states of He atoms. In addition, we present the first theoretical prediction of the energies and widths of high-lying doubly-excited resonance states of $^{1}$P$^{o}$ (n=8-15) in external dc electric field strengths of 3.915-10.44 kV/cm. The calculated dc-field perturbed high-lying resonance energies are in good agreement with the latest experimental data.   

Landau-Zener crossings in magnetically trapped polar molecules

Paramagnetic polar molecules generically exhibit a number of avoided crossings between Zeeman manifolds of opposite parities in combined magnetic and electric fields. In the context of a magnetic trap, these avoided crossings become opportunities for molecules to Landau-Zener hop to untrapped states. We have observed this behavior in a model system, magnetically trapped OH and achieve near-quantitative agreement with a simple Landau-Zener theory.   

THE IRON PROJECT \& THE IRON OPACITY PROJECT: Re-establishing the Sun as the Astrophysical Rosetta Stone

The aims of the two projects are detailed studies of radiative and collisional processes of astrophysically abundant atoms and ions, mainly iron and iron-peak elements, over a wide energy range, from infra-red to X-rays. One of the most fundamental astrophysical problem today is the discrepancy in the abundances of the most common volatile elements C, N, O, Ne, etc in the sun. These have been spectroscopically measured to be up to 50\% lower than the canonical abundances long employed in stellar interior models. A potential solution to this problem is if stellar opacities are at least 30\% higher, given the inverse but complex relationship between opacities and abundances. We report on new iron opacity calcultions, including hitherto neglected atomic physics of resonances which are largely treated as lines in existing opacities calculations. We also describe recent laboratory experiements of monochromatic opacities at the Sandia Z-pinch device. We will present Breit-Pauli R-matrix results for Fe~VIII with 567 fine structure levels with n $\leq$10, $l\leq$9, and 0.5$\leq J \leq$9.5, and 35,504 electric dipole allowed fine structure transitions. Results for forbidden transitions will also be presented.   

Enhancement of X-ray dose absorption for medical applications

Interaction of high-Z (HZ) elements with X-rays occurs efficiently at specific resonant energies. Cross sections for photoionization rapidly decrease after the K-edge; higher energy X-rays are mostly Compton-scattered. These features restrict the energy range for the use of HZ moities for radiosensitization in cancer therapy. Conventional X-ray sources such as linear accelerators (LINAC) used in radiotherapy emit a broad spectrum up to MeV energies. We explore the dichotomy between X-ray radiotherapy in two ranges: (i) E $<$ 100 keV including HZ sensitization, and (ii) E $>$ 100 keV where sensitization is inefficient. We perform Monte Carlo numerical simulations of tumor tissue embedded with platinum compounds and gold nanoparticles and compute radiation dose enhancement factors (DEF) upon irradiation with 100 kV, 170 kV and 6 MV sources. Our results demonstrate that the DEF peak below 100 keV and fall sharply above 200 keV to very small values. Therefore most of the X-ray output from LINACs up to the MeV range is utilized very inefficiently. We also describe experimental studies for implementation of option (i) using Pt and Au reagents and selected cancer cell lines. Resultant radiation exposure to patients could be greatly reduced, yet still result in increased tumoricidal ability.   

Inner shell resonances in the outer shell photoionization of Xe@C60

Fullerenes C$_{60}$ can be stuffed by almost all atoms A or even simple molecules. It is demonstrated by the example of the 5p-subshell of the Xe atom stuffed inside the C$_{60}$ fullerene, i.e. the endohedral Xe@C$_{60}$ that the so-called confinement resonances in 4d subshell strongly affect the absolute and differential in the photoelectron emission angle cross-section of 5p electrons photoionization in the region of 4d ionization threshold. It is a sort of a surprise that the narrow inner shell resonances are not smeared out in the outer shell photoionization cross-section. Inner shell resonances affect the outer cross-section by enhancing this enormously and modifying 5p dipole and non-dipole angular anisotropy parameters. Close to its own photoionization threshold, 5p photoionization cross-section of Xe@C$_{60}$ is dominated by its own confinement resonances greatly enhanced by the intensity of incoming radiation due to polarization of the C$_{60}$ electron shell by the incoming photon beam. In between, the 4d and 5p thresholds, the effect of 4d is becoming stronger while own resonances of 5p are becoming less and less important.   

MEMS-Based Beam Steering for Individual Addressing of Trapped Ions

The ability to address individual ions in a long linear chain with multiple beams is necessary in order to realize scalable quantum information processing with trapped ions. Microelectromechanical systems (MEMS) technology allows one to design movable micromirrors to focus laser beams on individual ions and steer the focal point in two dimensions. This system provides low optical loss across a broad wavelength range and can easily scaled to multiple beams. Our current MEMS system is designed to steer a far-detuned UV pulsed laser beam to carry out single and two qubit Raman gates on a chain of Yb ions, with a waist of 1.5 $\mu $m across a 20 $\mu $m range. The crosstalk between neighboring ions can be used to characterize the individual addressing fidelity in this setup. We also present a MEMS-based optical shutter that utilizes the fast switching speeds of the MEMS devices without introducing thermal instability or frequency shifts of the beam. The shutter system is comprised of input and output UV fibers with collimating microlenses, a focusing lens, and a single MEMS mirror. By tiling the MEMS mirror, the beam is steered off the output fiber and the light is decoupled. We show a high extinction ratio of $>$50dB with a throughput of 53{\%} and a switching speed of $\sim $2 $\mu $s.   

Linear chains in a monolithic symmetric trap for quantum information processing

Linear ion chains are being used [1] to simulate quantum magnet Ising interactions, phase transitions, and spin frustrations. We will present results for trapping linear ion chains in a monolithic two-level trap that utilizes the flexibility, complexity and scalability provided by VLSI silicon microfabrication. This trap provides optimized features and dimensions for trapping equally spaced ion chains while minimizing light scattering and exposed dielectrics that sometimes limit surface electrode ion traps. The ions are trapped symmetrically between two electrode layers. This geometry provides a strong pseudopotential well and radial field symmetry, resulting in stable ion mode frequencies and chains. \\[4pt] [1] K. Kim, et al, Phys. Rev. Lett. 103, 120502 (2009)   

Enhanced Single-Photon Multi-Detachment in Anions of C$_{60}$ and Observation of a Scaling Law

Absolute single-photon multi-detachment cross sections in C$_{60}^-$ have been measured. We observe a large enhancement (2 and 2.5 times for double and triple detachment, respectfully) of the oscillator strength in the anion compared to neutral C$_{60}$. Although the anion spectra is qualitatively similar to that of multi-photoionzation in C$_{60}$, the anion spectra are substantially compressed in photon energy. The effect of the additional screening provided by the excess electron in the anion on the knock-off process is proposed in order to explain the observed energy scaling. We can also deduce from the results that plasmon resonances do not couple strongly into two- and three-electron removal channels in either the anion or the neutral systems, a surprising result given the intrinsic multi-electron character of the plasmon resonances.   

Double Photoionization of Helium Atom using effective Charges

We will report the results of our investigation on double photoionization of helium atom using the recently extended MCHF method [1] for double photoionization of atoms. Calculation will be performed using wave functions for the initial and the final states with and without the electron correlation. The initial state wave function will be calculated using both the HF and MCHF methods The final state wave functions will be obtained using the asymptotic effective charge [2,3] to represent the electron correlation between the two final state continuum electrons. Using these wave functions, the triple differential cross sections will be calculated for 30 eV excess photon energy. The single and total integral cross sections will be obtained for photon energies from threshold to 300 eV. The results will be compared with the available experimental and the theoretical data. \\[4pt] [1] Hari P. Saha, J.Phys. B (submitted) \\[0pt] [2] M.R.H. Rudge, Rev. Mod. Phys. 40, 564 (1968) \\[0pt] [3] C.Pan and A.F Starace, Phys. Rev. Lett. 67, 185 (1991); Phys. Rev. A45, 4588 (1992)   

Coupled channel theory of photoionization microscopy

A quantum-mechanical coupled-channel theory is presented to simulate spatial distributions of electron probability density and current density, produced in photoionization of nonhydrogenic atoms in a uniform external electric field and recorded on a position-sensitive detector. Coupled equations for the multicomponent wavefunction are solved in mixed semiparabolic and parabolic coordinates. Using the theory, we predict distributions of electron probability density and current density produced in photoionization of the ground-state Li atom. The computed results are compared with experiment and very good agreement is found. The atomic core produces a significant effect in the electron probability density distribution in the vicinity of Stark resonances. The quantum tunneling effects in the presence of the atomic core are also analyzed.   

Dramatic quadrupole effects in the low energy photoionization of the 4$s$ subshell of free and confined Ca

The importance of first-order nondipole effects in low-energy photoionization is well known [1], and, the significance of second-order [O($k^{2}r^{2})$, where $k$ is the photon wave number] nondipole terms has been stressed even at photon energies as low as $\sim $11 eV [2]. In the present work, valence dipole and quadrupole photoionization of free atomic Ca and @Ca (Ca atom trapped in a C$_{60}$ cage) are investigated using the relativistic random phase approximation (RRPA) [3]. In the vicinity of the 4$s$ Cooper minimum ($\sim $ 10 eV) [4], second-order nondipole terms are found to induce dramatic changes in the photoelectron angular distribution over a small energy range, primarily due to contributions from quadrupole-quadrupole interferences. Also, the calculation of the dipole angular distribution parameter $\beta $ in the vicinity of the dipole Cooper minimum requires the inclusion of the quadrupole terms, as was found earlier [2]. Finally, the results show that confinement of the Ca atom in the fullerene cage augments the quadrupole effects still further.\\[4pt] [1] W. R. Johnson \textit{et al}, Phys. Rev. A \textbf{59}, 3609 (1999). [2] G. B. Pradhan \textit{et al}, J. Phys. B \textbf{44}, 201001 (2011). [3] W. R. Johnson and C.D Lin, Phys. Rev. A \textbf{20}, 978 (1979). [4] J. W. Cooper, Phys. Rev. \textbf{128}, 681 (1962). Lett.\textbf{ 105}, 233002 (2010). [5] C. H. Zhang and U. Thumm, Phys. Rev. A \textbf{82}, 043405 (2010). [6] W. R. Johnson and C. D. Lin, Phys. Rev. A \textbf{20}, 964 (1979). [7] J. W. Cooper, Phys. Rev. \textbf{128}, 681 (1962).   

Observation of Bound-Bound Transitions in the Negative Ion of Lanthanum La$^{-}$

The negative ion of lanthanum has been investigated with tunable infrared laser photodetachment spectroscopy. The relative signal of neutral atom production was measured with a crossed laser-ion beam apparatus over the photon energy range 0.29 -- 0.49 eV. The spectrum reveals a number of sharp peaks due to bound-bound electric-dipole transitions in La$^{-}$, observed here through a two-step process of excitation followed by photodetachment of the upper state. The transitions responsible for four of the peaks are identified through comparison to the calculations of O'Malley and Beck [1]. The richness of the observed bound state spectrum is unprecedented for atomic negative ions, and it highlights the uniqueness of La$^{-}$ for applications such as laser cooling.\\[4pt] [1] S.M. O'Malley and D.R. Beck, \textit{Phys. Rev. A} \textbf{81}, 032503 (2010).   

Two- and three-photon double ionization of lithium

Motivated by current FEL experiments at FLASH, we present triple differential cross sections and recoil ion momentum distributions for two- and three-photon double ionization of the 1s$^2$2s $^2$S ground state of lithium at a photon energy of 50 eV. The time-dependent close-coupling (TDCC) method is used to solve the two-electron time-dependent Schr\"{o}dinger equation in full dimensionality. The double ionization process is treated as a two-active-electron process, where the ``active'' 1s and 2s electrons move in the field of the ``frozen-core'' Li$^{2+}$ 1s state. Recent experimental measurements of recoil ion momentum distributions have observed features associated with the absorption of both two and three photons. This work provides the first TDCC calculations to date of such two- and three-photon double ionization processes in lithium. The accurate treatment of these processes requires a detailed description of the final continuum containing both singlet and triplet S, P, D and F waves. We examine triple differential cross sections as a function of electron energy sharing for a variety of angular configurations. We also compare our calculated recoil ion momentum distributions with experimental measurements, providing the first such comparison for two- and three-photon processes.   

Fourier photospectroscopy of Xe@C$_{60}$ in the Xe 4d giant resonance region: Testing the single-photoionization theory against recent measurements

We have developed a technique, based on Fourier-transforming cross sections to the reciprocal configuration space, to explore the electronic multiple interferences in the photoionization of endohedral fullerene molecules. Using this technique, the single photoionization cross section of endohedral Xe@C$_{60}$ over Xe 4d giant resonance energy region, calculated in the time dependent local density approximation (TDLDA), is compared with recent double photoionization experimental data [1]. The analysis of oscillatory cross sections derives a number of inherent similarities between the prediction and the data, including a large beating-type oscillation and several others of intermediate size [2]. Results stress the need for more accurate measurements to access the wealth of information about the geometry of the system.\\[4pt] [1] A.L.D. Kilcoyne et al., \textit{Phys. Rev. Lett.} \textbf{105}, 213001 (2010);\\[0pt] [2] A.B. Patel and H.S. Chakraborty, \textit{J. Phys.} B \textit{Fast Track Comm}. \textbf{44}, 191001 (2011).   

Photoionization of the Zn@C$_{60}$ endofullerene: Atom-fullerene ground-state orbital hybridization of d-d character

A detailed theoretical study of the subshell photoionization of Zn endohedrally confined in C$_{60}$ has been performed. The fullerene molecular core of sixty C$^{4+}$ ions is modeled by a classical jellium smearing, while the delocalized cloud of 240 carbon valence electrons, \textit{plus} the encaged Zn atom placed at the center of the cage, are treated in the time-dependent local density approximation (TDLDA) [1]. A powerful hybridization of the Zn 3d state with the 2d orbital near the low end of C$_{60}$ electronic band are unraveled. Cross sections for these hybrid states at both low photon energies, overwhelmed by electronic collective motions, and high energies of dominant single-electron behavior are presented. The results exhibit rich structures and are radically different from the cross sections of free atomic or free fullerene states participating in the hybridization process.\\[4pt] [1] M.E. Madjet et al., \textit{Phys. Rev. }A \textbf{81}, 013202 (2010).   

Ultrafast Energy Transfer between Oxygen Molecules

Photo ionization of atoms or molecules just above the double ionization threshold often leaves the cation in an excited state. The excess energy is mainly released by autoionization or radiative decay. For dimers Cederbaum \textit{et al.} have predicted a third process for relaxation. Here, the excited atomic or molecular target transfers the energy in form of a virtual photon to its neighboring partner, which emits an electron subsequently. The remaining doubly charged dimer then undergoes a Coulomb explosion. The effect is known as Interatomic Coulombic Decay (ICD) and has been observed for a variety of atoms so far. Only recently it was found to take place in water molecules as well. We report on the experimental study of this ultrafast energy transfer process in oxygen dimers.   

Dissociation Dynamics and Molecular Imaging of Methane following Photoionization at the Carbon K-Edge

We have used Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) to measure the momenta of the photoelectron and the molecular fragments arising from the dissociation of methane following core photoionization and subsequent Auger decay. We present results here that show (1) the full 3-D imaging of the molecule by the molecular frame photoelectron angular distribution; (2) the numerous dissociation pathways emerging from the unstable di- and tri-cations; (3) the dynamics associated with Jahn-Teller distortions in the breakdown of axial recoil behavior, where protons are only ejected along ground-state bond axes under certain conditions; and (4) the use of symmetries to improve statistics associated with measurements of this type. These results are compared with and interpreted through the use of Compex Kohn variational calculations.   

Theory of laser-dressed resonant Auger decay for ultraintense and ultrashort x rays

The emerging x-ray free electron lasers (FELs) such as the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory can reach very high x-ray intensities and ultrashort pulse durations. We develop a theory for the strong coupling of x rays with an atom, which couples core electrons with Rydberg states. In addition, we consider a near-infrared (NIR) laser that couples the Rydberg states among each other. We can theoretically describe several atomic systems with this setup using three-level ($\Lambda$-type and cascade-type are considered) models, which allow us to use electromagnetically induced transparency for x rays induced by the NIR laser. The theoretical models also allow us to calculate the NIR-laser-controlled Auger electron spectrum. We apply these models to predict the Auger electron spectrum of Ne ($\Lambda$-type) and Ne$^+$ (cascade-type). This work opens up new prospects to study and analyze the interaction of ultraintense and ultrashort x rays with atoms.   

Laser-Induced Electron-Positron Pair Creation -- Relevance of Phase Effects

With recent technological progress and experimental availability of extremely powerful lasers, yielding a ponderomotive energy shift of the order of magnitude $m_{\rm e}c^2$ and beyond, it has become of interest to reexamine fundamental processes of quantum electrodynamics (QED); in particular, the formation of electron-positron pairs by means of laser radiation [1]. The electron-positron pair creation in collisions of a relativistic nucleus with a two-color laser field is investigated using the standard approach of QED [2]. We consider the case when both components of the laser field have commensurate frequencies and comparable strengths. We analyze the dependence of both the angular distributions of created particles and the total probability rates of pair production on a phase coherence of a driving laser field.\\[4pt] [1] F. Ehlotzky, K. Krajewska, and J. Z. Kami\'nski, Rep. Prog. Phys. {\bf 72}, 046401 (2009).\\[0pt] [2] K. Krajewska and J. Z. Kami\'nski, Phys. Rev. A (submitted).   

Exploring the high-order harmonic generation from Rydberg states with a fixed Keldysh parameter

The commonly adopted viewpoint that the Keldysh parameter $\gamma$ determines the dynamical regime of ionization in strong field physics has long been demonstrated to be a misleading one. One can then ask what happens in strong field ionization as relevant parameters, such as laser intensity and frequency, are varied while keeping $\gamma$ fixed. We present results from our simulations of high-order harmonic generation (HHG) from Rydberg states of a hydrogen atom. We calculate high harmonic spectra from various initial states with $n$ up to 42, where the laser intensities and the frequencies are scaled from those for $n=1$ in order to maintain a fixed Keldysh parameter $\gamma<1$. We find that as we go up in $n$ for a fixed $\gamma$, the position of the cut-off scales as $\sim$$1/n^2$ in terms of the cut-off law predicted by the three-step model for $n=1$. However, a secondary cut-off structure forms below this, which moves to lower harmonics as $n$ is increased. This second cut-off splits the plateau into two regions, one higher in yield and below the second cut-off, and the second with lower yield following it. We further investigate the final $n$-distributions for some of the interesting cases to elucidate the physical mechanism leading to this structure   

Precision treatment of single and double multiphoton ionization of He atoms by strong laser fields: Time-dependent generalized pseudospectral method in internal coordinates

We have developed a new computational method for accurate and efficient numerical solution of the time-dependent Schr\"odinger equation for two-electron atoms. Our approach is full-dimensional and makes use of the internal coordinates of the electrons in the plane defined by the electrons and the nucleus ($r_{1}$, $r_{2}$, and $\theta_{12}$) as well as Euler angles which determine the orientation of the plane in space. The internal coordinates can be optimally discretized by means of the generalized pseudospectral method while the Euler angles appear through the basis set functions with the definite total angular momentum and its projections. The results of the single and double ionization of the helium atom by strong 800~nm laser fields will be presented. The accurate time-dependent electron density obtained can be used for testing and improvement of various approximate exchange-correlation functionals of the time-dependent density functional theory.   

Density-Functional Theory with Optimized Effective Potential and Self-Interaction Correction for the Double Ionization of He and Be Atoms

We present a \textit{self-interaction-free} (SIC) time-dependent density-functional theory (TDDFT) for the treatment of double ionization processes of many-electron systems. The method is based on the Krieger-Li-Iafrate (KLI) treatment of the \textit{optimized effective potential} (OEP) theory and the incorporation of an explicit self-interaction correction (SIC) term. In the framework of the time-dependent density functional theory, we have performed 3D calculations of double ionization of He and Be atoms by strong near-infrared laser fields. We make use of the exchange-correlation potential with the integer discontinuity which improves the description of the double ionization process. We found that proper description of the double ionization requires the TDDFT exchange-correlation potential with the discontinuity with respect to the variation of the spin particle numbers (SPN) only. The results for the intensity-dependent probabilities of single and double ionization are presented and reproduce the famous ``knee'' structure.   

Fragmentation dynamics of Ar$_{2}^{+}$ dimers in intense laser fields

We studied the fragmentation dynamics of the Ar$_{2}$ dimers in 790 nm pump and 1400 nm probe pulses with intensities of 10$^{14}$ W/cm$^{2}$ by analyzing kinetic energy release (KER) spectra as a function of the pump probe delay. The KER spectra are measured by detecting Ar-ion fragments in a COLTRIMS [1] setup and are compared with model calculations based on the numerical propagations of the time-dependent Schr\"{o}dinger equation [2]. The measured spectra are best reproduced by two-state calculations that include the adiabatic electronic states I(1/2)$_{u}$ and II(1/2)$_{g}$ of Ar$_{2}^{+}$, dipole coupled in the pump- and probe-laser electric fields. \\[4pt] [1] J. Wu, A. Vredenborg, B. Ulrich, L. Ph. H. Schmidt, M. Meckel, S. Voss, H. Sann, H. Kim, T. Jahnke, and R. D\"{o}rner, PRA \textbf{83}, 061403(R) (2011) \\[0pt] [2] M. Magrakvelidze, F. He, Th. Niederhausen, I. V. Litvinyuk, and U. Thumm, PRA \textbf{79}, 033410 (2009).   

Strong-field control of coherent anti-Stokes Raman scattering in iodine vapor with shaped ultrashort laser pulses

Extensive work has been done to investigate molecular dynamics in weak laser fields. In contrast, our understanding of molecular behavior and the possibilities to control it with strong laser pulses is still limited. In this work, we investigate the process of coherent anti-Stokes Raman scattering (CARS) in iodine vapor for different strong-field regimes. Saturation of the CARS signal with increasing pulse intensities is observed and studied both experimentally and theoretically. We show that it is possible to overcome this saturation by implementing different schemes of coherent control based on the technique of femtosecond pulse shaping. Optimal regimes for enhancing molecular CARS response to strong-field excitation are proposed and demonstrated, paving the way to more efficient nonlinear spectroscopy.   

X-ray--optical cross correlator for gas-phase experiments at the LCLS free-electron laser

X-ray--optical pump--probe experiments at the Linac Coherent Light Source (LCLS) have so far been limited to a time resolution of 280\,fs fwhm due to timing jitter between the accelerator-based free-electron laser (FEL) and optical lasers. We have implemented a single-shot cross-correlator for femtosecond x-ray and infrared pulses. An independent reference experiment relying only on the pulse arrival time information from the cross-correlator shows a time resolution better than 50\,fs fwhm (22\,fs rms) and also yields a direct measurement of the maximal x-ray pulse length. The improved time resolution enables ultrafast pump--probe experiments with x-ray pulses from LCLS and other FEL sources. Reference: S. Schorb et al., Appl. Phys. Lett. 2012 in press   

Moving towards strong-field femtosecond control of bond cleavage and charge localization in triatomic molecules

A 3-D momentum imaging technique is employed to study intense ultrafast laser-induced dissociation of triatomic molecular ions from an ion beam. Utilizing our measured kinetic energy release and angular distribution spectra along with the calculated electronic structure of these molecules, we elucidate possible dissociation pathways and anticipate and explore various laser parameters that could be used to drive transitions to specific final products. For example, we have studied N$_{2}$O$^{+}$, in which we find that for typical intense IR laser pulses ($\sim $30 fs, transform-limited, 800 nm, $\sim $10$^{15}$ W/cm$^{2}$ pulses), the preferred bond cleavage ($i.e.$, breaking the N-N bond vs. the N-O bond) and charge localization patterns are those that are the most energetically favorable. We investigate laser parameters that could be used to steer this and other systems to less likely outcomes.   

DC and subcycle-resolved AC Stark shifts in Helium

We are developing a finite element discrete variable representation (FE-DVR) code to model the response of two-electron atoms to ultra-short pulses of EM radiation. Our first numerical results for the DC stark shift of helium deviate significantly from previous [1] single-active-electron (SAE), but are in close agreement with improved SAE calculations that include the effect of core polarization in the external field. For 3x10$^{14}$ W/cm$^{2}$ infra red fields, we calculate sub-IR-cycle- resolved instantaneous (AC) level shifts of low-lying bound He states that also strongly deviate from the SAE prediction [1]. We plan to apply our code to model recently measured subcycle time-resolved absorption spectra [2].\\[4pt] [1] F. He, C. Ruiz, A. Becker, and U. Thumm, J. Phys. B \textbf{44}, 211001 (2011).\\[0pt] [2] H. Wang, M. Chini, S. Chen, C.-H. Zhang, F. He, Y. Cheng, Y. Wu, U. Thumm, and Z. Chang, Phys. Rev. Lett. \textbf{105}, 143002 (2010); M. Chini, Z. Chang \textit{et al.}, to be published.   

Toward understanding the breakup mechanism of triatomic molecular ions in an intense laser field

Studies of laser-induced dissociation and ionization of triatomic molecular ions is a key step toward understanding the breakup mechanisms of complex systems in an intense laser field. This study is focused on two questions: (1) Does a triatomic molecular ion XY$_{2}^{+}$ bend during the interaction with a strong ultra-short laser field? (2) What is the preferred dissociation or ionization alignment relative to the laser polarization of such molecular ions? We implement a coincidence three dimensional momentum imaging technique, which allows us to measure all the neutral and charged fragments of any breakup channels of a triatomic molecular ion in coincidence. For example, we have studied a CO$_{2}^{+}$ ion beam, exposing it to intense 30 fs, 790 nm laser pulses with intensity up to 10$^{15}$ W/cm$^{2}$, in order to address the above questions.   

Atomic hyperpolarisabilities and the non-linear optics of atomic gases

The properties of one and two-electron atoms are calculated numerically using configuration interaction and perturbative methods. We present calculations here the dynamic hyperpolarisabilities of these atoms, the emphasis here being on low-energy fields of interest in atomic clocks, and high-energy excitations that probe near Rydberg states. The variance of transition energies and magic wavelengths with hyperpolarisability will be discussed. Two forms of the susceptibilities, $\chi_3(\omega,I)$, that describe the non-linear optics of atoms in electric fields, will be presented that describe the variation of the refractive index of an atomic gas in ground or excited states, as well as third-harmonic generation.   

Single- and Multiple-Electron Removal Processes in Proton-Water Vapor Collisions

Charge-state correlated cross sections for single- and multiple-electron removal processes due to capture and ionization in proton-$\rm H_2O$ collisions are calculated by using the non-perturbative basis generator method adapted for ion-molecule collisions [1]. Orbital-specific cross sections for vacancy production are evaluated using this method to predict the yields of charged fragments ($\rm H_2O^+, OH^+, H^+, O^+$) according to branching ratios known to be valid at high impact energies. At intermediate and low energies, we obtain fragmentation results on the basis of predicted multi-electron removal cross sections, and explain most of the available experimental data [2]. The cross sections for charge transfer and for ionization are also compared with recent multi-center classical-trajectory Monte Carlo calculations [3] for impact energies from 20keV to several MeV. \\[4pt] [1] H.J. L\"udde et al, Phys. Rev. A {\bf 80}, 060702(R) (2009)\\[0pt] [2] M. Murakami et al, to be submitted to Phys. Rev. A (2012)\\[0pt] [3] C. Illescas et al, Phys. Rev. A {\bf 83}, 052704 (2011)   

Elastic and Inelastic Collisions of Single Cs Atoms with an Ultracold Rb Cloud

Ultracold gases doped with impurity atoms are promising hybrid systems that pave the way for investigation of a series of novel and interesting scenarios: They can be employed for studying polaron physics, the impurity atoms can act as coherent probes for the many-body system, and the coherent cooling of neutral atoms containing quantum information has been proposed. Here, we immerse single and few Cs atoms into an ultracold Rb cloud. Elastic collisions lead to rapid thermalization of both sub-systems, while inelastic collisions lead to a loss of Cs from the trap. When thermalized, the impurity atom is localized inside the Rb gas. The ultracold Rb gas remains effectively unaffected by the interaction with the Cs impurity atoms. The poster will present details of the experimental setup, sequence and data analysis needed to extract the interspecies scattering length and three-body loss coefficient from the thermalization dynamics and loss rates measured.   

Ionization in collisions between metastable hydrogen atoms

Associative and Penning ionization cross sections are calculated for collisions between metastable hydrogen 2s atoms at thermal energies. Cross sections for deuterium 2s collisions are also reported. The associative ionization cross sections behave as $E^{-1}$ for collision energy $E$, in agreement with an existing experiment. The Penning ionization cross sections dominate for all energies and are found to follow the $E^{-2/3}$ behavior that was predicted in previous work for the total ionization cross section. The magnitudes of our theoretical associative ionization cross sections for H(2s)+H(2s) collisions are between two and four times larger than the experimental data.   

Transfer of atomic alignment in alkali systems

The well-known phenomenon of ``spin exchange'' has been thoroughly characterized in alkali-alkali collisions, and atomic orientation is easily transferred between different alkali isotopes. Nevertheless, collisional transfer of higher-order polarization moments (such as atomic alignment) has received little attention in the literature. Such alignment transfer should be forbidden in sudden binary collisions of alkali atoms, but it is reasonable to question at what level. Here we discuss recent experiments to place limits on this alignment-exchange rate between isotopes of rubidium and cesium in a room-temperature vapor cell.   

Theoretical Studies of Dissociative Recombination of Electrons with N$_2$H$^+$ Ions

We are investigating the dissociative recombination (DR) of electrons with the molecular ion N$_2$H$^+$. (The process is $e^- + \mathrm{N}_2\mathrm{H}^+ \rightarrow \mathrm{N}_2 + \mathrm{H}$.) $\mathrm{N}_2\mathrm{H}^+$ is found in the interstellar medium, and a better understanding of the DR process will aid the development of astrophysical models. For a quantitative DR study of N$_2$H$^+$, an even-handed treatment of the excited valence and Rydberg surfaces of N$_2$H is required. We are currently performing large scale multi-reference configuration interaction (MRCI) electronic structure calculations to obtain these highly excited-state surfaces of N$_2$H. The effects of strong Rydberg-valence mixing in excited N$_2$H are then disentangled to identify the primary dissociating surface that governs the DR process. This work is based on using the block diagonalization method to determine diabatic potential surfaces. The surfaces have been calculated at several different values of the NH distance and the NN--H bond angle. Preliminary results indicate that the direct method cross section is small at low energies which suggests the indirect method (or Renner-Teller effect) may play a role in the DR process. The current status of this work will be presented at the conference.   

Electron Impact Ionization of He atom using screening potential

We will report the results of our investigation on electron impact ionization of helium atom using our extended MCHF method [1] for electron impact ionization of atoms. The initial state wave function will be calculated with both HF and MCHF approximations and the electron correlation between the two final state continuum electrons will be obtained using the screening potential [2-4]. Calculations will be made for triple differential cross sections for 4 eV excess energy sharing equally by the two final state continuum electrons. The results will be presented for all scattering angles and all kinematics. Comparison will be made with available experimental and theoretical data. \\[4pt] [1] Hari P. Saha, Phys. Rev. A82, 042703 (2010); J.Phys. B44, 065202 (2011).\\[0pt] [2] M.R.H. Rudge and M.J. Seaton, Proc. Roy. Soc. A293. 262 (1965).\\[0pt] [3] M.R.H. Rudge, Rev. Mod. Phys. 40, 564 (1968).\\[0pt] [4] C.Pan and A.F Starace, Phys. Rev. Lett. 67, 185 (1991); Phys. Rev. A45, 4588 (1992).   

Resonances in slow electron collisions with In, Tl, Ga and At atoms: Accurate electron affinities

The complex angular momentum (CAM)-calculated low-energy electron elastic total cross section (TCS) for In is benchmarked through its recently measured electron affinity (EA) [1]. The CAM method is then used to calculate the TCSs for Tl, Ga and At atoms. From the dramatically sharp resonances in the TCSs, binding energies (BEs) for Tl-, Ga- and At- formed during the collisions as Regge resonances are extracted and compared with the existing experimental and theoretical values. Notably, our calculated BE for the first excited state of Tl- agrees excellently with the EAs of [2, 3]. However, our EA for Tl is 2.415 eV. Consequently, we conclude that the published theoretical and experimental EAs for Tl correspond to the BE of the first excited state of Tl and not to the EA value. This calls for immediate experimental verification. \\[4pt] [1] C.W. Walter et al, Phys. Rev. A 82, 032507 (2010) \\[0pt] [2] F. Arnau et al, Chem. Phys. 166, 77 (1992) \\[0pt] [3] W. P. Wijesundera, Phys. Rev. A 55, 1785 (1997)   

Electron-hydrogen cross section computation for astrophysical applications

Our contribution focuses on the electron-hydrogen scattering and is intended as an extension of available atomic databases (e.g [1]) used by the astronomers and stellar/solar physicists. These databases often lack required precision and sometimes even major resonances, which are essential for correct transition rates extraction and thus for the description of astrophysical phenomena. Our aim is to obtain a controlled approximation of scattering cross section energy dependence for all relevant energies and (de)excitational transitions. The poster summarises results computed by freely available (e.g. [2], [3]) computer codes and compares them with our original results. Low energy cross sections -- up to this time a domain of R-matrix packages -- have been recomputed using exterior complex scaling implemented in B-splines (see [4]), whereas higher energies using different types of Born approximation.\\[4pt] [1] The Aladdin database at http://www-amdis.iaea.org/ALADDIN/\\[0pt] [2] UK RmaX at http://amdpp.phys.strath.ac.uk/UK$\_$RmaX/\\[0pt] [3] Scott et al., Comp. Phys. Comm. 180 (2009) 2424--2449.\\[0pt] [4] McCurdy, Rescigno, J. Phys. B: At. Mol. Opt. Phys. 37 (2004) 917--936.   

Importance of final state electron-electron interactions in the Triple Differential Cross Sections for Electron Impact Ionization of Neon

Three-dimensional triple differential cross sections have been calculated and measured for 61eV electron-impact ionization of the 2p state of neon. Three-dimensional distributions for the ejected electron will be presented for a fixed incident projectile energy and scattered projectile angles ranging between 20 degrees and 70 degrees and ejected electron energies ranging between 2eV to 20eV. The theoretical model used for the calculations is the DWBA (distorted wave Born approximation). The importance of PCI (post collision interaction between the scattered and ejected electron) will be examined by either including or excluding this effect in the final state wavefunction. The importance of the interaction between the ejected electron and the residual atomic electrons will be examined by comparing results using distorted waves calculated in a static potential with Hartree-Fock distorted waves.   

Differential cross sections for electron-impact excitation of the electronic states of pyrimidine

Pyrimidine (C$_{4}$N$_{2}$H$_{4})$ is an important molecule, as it forms the basis of larger biomolecules, such as the DNA bases thymine, cytosine and uracil. There is a pressing demand for low-energy electron scattering data from such biological analogs in order to model radiation induced damage [1]. We therefore present the first measurements for absolute differential cross section data for low-energy electron-impact excitation of the electronic states of pyrimidine. The present measurements were performed using a crossed-beam apparatus [2] for incident electron energies ranging between 15 to 50eV while covering a 10 to 90$^{\circ}$ angular range. Here the absolute scale has been determined through a normalisation to the recently measured elastic scattering differential cross section data for pyrimidine [3]. [1] F. Ferreira da Silva, D. Almeida, G. Martins, A. R. Milosavljevic, B. P. Marinkovic, S. V. Hoffmann, N. J. Mason, Y. Nunes, G. Garcia and P. Limao-Vieira, \textit{Phys Chem Chem Phys} \textbf{12}, 6717 (2010). [2] M. J. Brunger and P. J. O. Teubner, \textit{Phys Rev A} \textbf{41}, 1413 (1990). [3] P. Palihawadana, J. Sullivan, M. Brunger, C. Winstead, V. McKoy, G. Garcia, F. Blanco and S. Buckman, \textit{Phys Rev A} \textbf{84}, 062702 (2011).   

Integral Cross Sections for Electron Impact Excitation of Rydberg and Valence States of Molecular Nitrogen

We present integral cross sections (ICSs) for electron impact excitation of N$_{2}$ out of the ground state $X (v$=0), to the $b$, $c_{3}$, $o_{3}$, $b', c'_{4}$, $G$, and $F$ electronic states at incident energies ranging between 17.5 eV and 100 eV. The ICSs were derived from the differential cross sections (DCSs) of Khakoo \textit{et al}. [Phys. Rev. A \textbf{77}, 012704 (2008)], which were obtained by unfolding energy loss spectra in the $\sim $12-13.82 eV range. Recently, Heays \textit{et al}. [Phys. Rev. A \textbf{85}, 012705 (2012)] measured comparable higher resolution energy loss spectra, with a significantly different apparatus configuration, but in agreement with the Khakoo \textit{et al}. (2008) spectra. This latter additional effort provided further confidence in the accuracy of the DCSs upon which the present ICS results are based. Of the higher-lying states studied, five are singlet states that radiate to the ground state via dipole allowed transitions. These include the $b$ and $b'$ valence states and the $c'_{4}$ Rydberg state that give rise to the Birge-Hopfield I, II, and Carroll-Yoshino bands, respectively, all of which are observed in the atmospheres of Earth, Titan, and Triton. The $c_{3}$ and $o_{3}$ Rydberg states give rise to the Worley-Jenkins and Worley series of Rydberg bands, respectively. However, these emissions are not readily observed since predissociation for the $c_{3}$ and $o_{3}$ states approaches 100{\%}. As such, direct electron excitation measurements, such as those presented here are superior to standard (spontaneous) emission based measurements in this case.   

Nonlocal resonance model for two nuclear degrees of freedom

A nonlocal resonance model (NRM) [W. Domcke, Phys. Rep. 208, 97 (1991)] is a commonly used method of calculating cross sections for elastic and inelastic processes in resonant electron-molecule collisions. Up to now, there has been a great number of studies devoted to implement this approach for molecules with only one nuclear degree of freedom (e.g. N$_2$, H$_2$, HCl etc) In the present work we developed a generalization of the NRM for two degrees of freedom. For testing purposes we have constructed two dimensional model, which captures essential features of resonant collisions of electrons with the CO2 molecule. Final cross sections for few chosen vibrational excitations are being compared with results obtained via a local complex potential approximation, which is so far the only approach dealing with multidimensional phenomena [C.W. McCurdy et al, Phys. Rev. A 67, 042708 (2003)]. We also discuss difficulties arising, when one chooses to work in a time dependent or a time independent formalism.   

Breaking a tetrahedral molecular ion with electrons: Study of NH$_4^+$

We apply a general theoretical model to study the dissociative recombination of the polyatomic ion NH$_4^+$. The high symmetry of the molecule, represented by the tetrahedral group, leads to complex vibronic couplings responsible for dissociative recombination. By applying multi-channel quantum defect theory and using symmetry considerations, we treat the doubly and triply degenerate modes and electronic states of NH$_4^+$ to calculate a theoretical cross section which agrees well with existing experimental data. This represents, to our knowledge, the first DR study for a molecular ion with triply degenerate electronic states and normal modes.   

Experimental and theoretical investigation of the triple-differential cross sections for electron impact excitation-ionization of aligned H2 for different orientations of the molecule

Most experiments measuring electron-impact ionization of molecules do not determine the orientation of the molecule at the time of ionization. One way to determine the orientation is to simultaneously ionize the molecule and excite the residual ion to a state that will dissociate. The orientation of the molecule can then be determined by detecting one of the dissociation fragments since the fragments will leave in the direction of orientation. Experimental and theoretical TDCS (triple differential cross sections) results will be presented for excitation-ionization of three excited states of H2 for three different orientations of the molecule at an incident electron energy of 176 eV.   

Comparison of positron and electron binding to molecules

Positrons can attach to molecules via Feshbach resonances in which a vibrational mode absorbs the excess energy. Using a high-resolution positron beam, this process has been used to measure positron-molecule binding energies for many chemical species.\footnote{G. F. Gribakin, et al., Rev. Mod. Phys. {\bf 82}, 2557 (2010).}$^,$\footnote{J. R. Danielson, et al., Phys. Rev. A, in press (2012).} In particular, recent measurements have focused on molecules with large permanent dipole moments (i.e., $\mu > 2.5$ D), including aldehydes, ketones, and nitriles. Positron binding to these molecules is compared to the analogous weakly bound electron-molecule (negative-ion) states, commonly called ``dipole-bound'' states.\footnote{N.~I.~Hammer, et al., J. Chem. Phys. {\bf 119}, 3650 (2003).} Positron binding energies are found to be one to two orders of magnitude larger than those of the negative ions due to two effects: the orientation of the molecular dipole moment allows the positron to approach it more closely; and for positrons, lepton correlations (e.g., via dipole polarizability) contribute more strongly. Comparisons to available calculations will be presented, as will comparisons to binding to molecules with $\mu\sim 0$ (e.g., polarizability bound states).   

Positron Binding to Molecules: Interplay between permanent dipole moments and polarizability

Energy resolved studies of positron-molecule collisions exhibit vibrational Feshbach resonances in annihilation, thus providing evidence that positrons can bind to these pecies.\footnote{G. F. Gribakin, et al., Rev. Mod. Phys. {\bf 82}, 2557 (2010).} The downshifts of the observed resonances provides a measure of the positron-molecule binding energies which range from 1 to 300 meV. Presented here are annihilation spectra and binding energies for a wide range of chemical species, including aldehydes, ketones, formates, acetates, nitriles, alcohols, and halogenated compounds.\footnote{J. R. Danielson, et al., Phys. Rev. A, in press (2012).}$^,$\footnote{A. C. L. Jones, et al., New J. Phys., in press (2012).} Within a group, the measured binding energies often show an approximate linear correlation with molecular dipole polarizability. However, other effects, including the permanent dipole moment ($\mu$) and molecular geometry, play significant roles as well. For example, for compounds with $\mu \geq 2$ D, it appears that localization of the positron wave function leads to enhanced binding and an increased dependence upon both $\mu$ and electron-positron correlations.\footnote{Danielson, op. cit.} The relationship of these results to theoretical calculations is discussed.   

Statistical Multimode Resonant Annihilation of Positrons on Molecules

Annihilation at positron energies in the range of the molecular vibrational modes is dominated by large-amplitude vibrational Feshbach resonances (VFR) in which the positron attaches to the molecule.\footnote{G. F. Gribakin, J. A. Young, C. M. Surko, Rev. Mod. Phys. {\bf 82}, 2557 (2010).} In small molecules, there is a quantitative description of the annihilation rates, $Z_{\rm eff}$, due to the VFR.\footnote{G. F. Gribakin, C. M. R. Lee, Phys. Rev. Lett. {\bf 97}, 193201 (2006).} Here we focus on a broad spectrum of enhanced annihilation that is observed in the spectra of many, if not most, molecules.\footnote{A. C. L. Jones, et al., Phys. Rev. Lett., in press (2012).} This spectral component, for example, dominates the spectra in small molecules with relatively large binding energies, such as CCl$_4$ and CBr$_4$. A model that assumes excitation and escape from a statistically complete ensemble of multimode vibrations is presented\footnote{G. F. Gribakin, C. M. R. Lee, European Phys. J. D {\bf 51}, 51 (2009).} that reproduces key features of the data. Related issues of intramolecular vibrational redistribution (IVR), and the effects of escape channels on the primary VFRs will also be discussed.   

Dissociation-aided state preparation and spectroscopy of trapped molecular ions

Preparation of state-selective ensembles of cold molecules is a promising starting point for precision molecular spectroscopy. Ion traps provide an ideal environment for rovibrational cooling of diatomic molecules. Ion trap life times are typically greater than hours and the Coulomb force ensures long internal-state coherence times. Additionally, co-trapped and laser-cooled atomic species provide sympathetic translational cooling down to mK temperatures. The fluorescence of the co-trapped atomic species can be used as a diagnostic for molecule formation and dissociation, with additional flexibility arising when the dissociating atomic ion is the same species as the coolant ion. Presented here are prospects for this type of spectroscopy using a Barium ion trap.   

Progress In Doppler Cooling of SiO$^{+}$

The rich internal structure which makes molecular ions interesting is exactly what makes them difficult to Doppler cool. Rotation and vibration within the molecule results in additional dark states which require repumping, and higher-order processes such as photodissociation and predissociation may terminate the cycling transition. We have identified SiO$^{+}$ as a promising candidate for laser cooling, and we present our current experimental progress towards cooling both the external and internal degrees of freedom.   

A new shape resonance in the Ps$^{-}$ system

There have been continues experimental and theoretical investigations on the positronium negative ion (Ps$^{-})$, one of the simplest three-lepton systems interacting through Coulomb forces. In the present work, we use highly correlated Hylleraas wave functions up to N=1078 terms together with employing the complex-coordinate rotation method [1] to investigate resonances in the Ps$^{-}$ system. We have located a new$ S$-wave shape resonance lying above the Ps ($n$=2) threshold. Our preliminary results for the resonance parameters are $E_{r }$= - 0.0498788 a.u. and \textit{$\Gamma $ }/ 2 = 0.0139470 a.u., where $E_{r}$ and $\Gamma$ denote the resonance energy and width, respectively. This stabilized complex eigenvalue has never been reported in the literature, to the best of our knowledge. Here, by changing the mass of the positively charged particle from one unit of the electron mass to infinitely heavy, we have traced this resonance pole from the positronium negative ion to the hydrogen negative ion [2]. Detailed calculations will be presented at the meeting. \\[4pt] [1]. Y. K. Ho, \textit{Phys. Reports} \textbf{99}, 1 (1983) and references therein. \\[0pt] [2]. A. Burgers and E. Lindroth, \textit{Euro. Phys. J. D} \textbf{10}, 327 (2000).   

On thermalization of positrons in water vapour

Water being the main component of the human tissue is the primary candidate for the basis of models describing positron diagnostics and therapy. Our calculations are based on the elementary binary cross sections measured or calculated. We use a Monte Carlo code following all individual collisions and trajectories allowing for the addition of external fields and accurate representation of non-conservative processes. In order to obtain realistic results completeness should be achieved for energy, momentum and number balances. Rather than determining transport coefficients which have only been measured in few cases for positrons we determine other observables. We determine the thermalization of a group of positrons released at a point in water vapour. The thermalization times may be scaled using Nt scaling. We also calculate the range of positrons, the corresponding diffusion coefficient and show shapes of individual trajectories. Finally we also establish the energy loss spectrum on the basis of binary processes. This allows us comparisons with other codes used to model transport of positrons.   

Charge Transfer, Ionization, and Excitation in Collisions between Protons and the Ions He$^+$, Li$^{2+}$. Be$^{3+}$, B$^{4+}$, and C$^{5+}$

Coupled-state cross sections are being determined for electron transfer, ionization, and excitation in collisions between keV- to MeV-energy protons and the hydrogenic ions He$^+$, Li$^{2+}$, Be$^{3+}$, B$^{4+}$, and C$^{5+}$, extending work reported 25 years ago with a limited basis for electron transfer and ionization only, over a limited energy range below the peak in the ionization cross section.\footnote{T. G. Winter, Phys. Rev. A {\bf 35}, 3799 (1987).}; the first and last processes [with the ions He$^+$ and C$^{5+}$] were also considered in related studies.\footnote{T. G. Winter and J. R. Winter, Phys. Rev. A {\bf 61}, 052709 (2000).}$^,$\footnote{T. G. Winter, Phys. Rev. A {\bf 69}, 042711 (2004)).} The presently used one- and two-center Sturmian bases are similar to those in the recent large-basis calculations for antiproton-H($1s$) atom collisions.\footnote{T. G. Winter, Phys. Rev. A {\bf 83}, 022709 (2011).}. Detailed convergence studies are being carried out, and scaling rules with nuclear charge are being re-examined, as are connections with perturbative results for all three processes, including Born cross sections for excitation into individual lower excited states.   

Charge Transfer in Collisions between Molecular Ions and Atomic Hydrogen/Deuterium$^{1}$

Using the Oak Ridge National Laboratory ion--atom merged--beams apparatus, absolute cross sections of direct and dissociative charge transfer (CT) between H/D and different molecular ions (D$_{2}^{+}$, CO$^{+}$, and O$_{2}^{+})$ are measured from 20 eV/u to 2 keV/u collision energies. Toward high energy where the differences in Q-value of the reaction can be neglected and the rovibrational modes can be considered as frozen, the measured cross sections for the diatomic ions all converge to (7 $\pm $ 0.5) x 10$^{-16}$ cm$^{2}$ at 2 keV/u and are consistent with a rovibrational frozen (H$_{2}^{+}$, H) calculation (Physical Review A 84, 062716, 2011). Below one keV/u collision energy, the measured cross sections exhibit trends which are compared to previous merged-beams measurements of CT with H for atomic ions with a variety of electrons on the core. \\[4pt] $^{1}$Research supported by the NASA Solar {\&} Heliospheric Physics Program NNH07ZDA001N, the Office of Fusion Energy Sciences and the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy, the National Science Foundation through Grant No. PHY-106887.   

Ionization of Rydberg Atoms in Controlled Surface Electric Fields

Earlier work shows that the ionization of xenon Rydberg atoms at metal surfaces is strongly influenced by the presence of stray patch fields. In the present work lithographically patterned electrode arrays comprising two interleaved ``combs'' are used to generate controlled surface electric fields by applying different potentials to each ``comb.'' Xenon ions produced near the surface are collected by an ion collection field applied perpendicular to the surface. With equal biases applied to the electrodes, the observed ion signal increases rapidly with increasing ion collection field above some threshold eventually saturating when each incident Rydberg atom is detected as an ion. Application of surface electric fields leads to a dramatic increase in the ion signal seen at low ion collection fields due to field ionization in the surface field well above the surface. The data are in good qualitative agreement with the predictions of a simple ionization model and suggest that such surface field ionization could allow efficient detection of low-n Rydberg atoms.   

Optimal Control Bounds of Molecular Orientations in Finite Temperatures

We investigated the optimal control bounds for the orientation of molecular systems in finite temperatures. The upper bounds of orientation controls are known to depend on both the temperature that determines the initial mixed states and the number of rotational states that can be excited by laser pulses. We considered the OCS molecule as an example to numerically demonstrate that a high degree of field-free-orientation can be achieved by optimally shaped pump fields in THz region [1]. To this end, we have implemented a fast monotonically convergent iterative procedure to obtain optimal orientation control pulses, by extending our recently formulated two-point boundary-value quantum control paradigm (TBQCP) for the pure-state optimal control problems [2-4] to the mixed-state ones. It was found that the degree of orientation could achieve 0.83 dynamically, which is 96{\%} of the kinematical maximum, at T=100K.\\[4pt] [1] Sharly Fleischer, Yan Zhou, Robert W. Field, and Keith A. Nelson, Phys. Rev. Lett. 107, 163603 (2011).\\[0pt] [2] Tak-San Ho and Herschel Rabitz, Phys. Rev. E 82, 026703 (2010)\\[0pt] [3] Emanuel F. de Lima, Tak-San Ho, Herschel Rabitz, Chem. Phys. Lett. 501, 267 (2011).\\[0pt] [4] Sheng-Lun Liao, Tak-San Ho, Shih-I Chu, and Herschel Rabitz, Phys. Rev. A \textbf{84}, 031401 (2011).   

Control of ground state quantum beats in Cavity QED

Ground state quantum beats oberserved in the second order intensity correlation from a continuously driven atomic ensemble inside a two mode optical cavity are subject to decoherence. While driving the cavity with light of linear polarization ($\pi$ transitions) the second order autocorrelation function is measured in the undriven mode (orthogonal polarization): a first photon detection prepares a superposition of atomic ground-state Zeeman sublevels and the second measures the ground state beats. Between these two detections, the atoms can become excited and return to the ground state, emitting a photon back into the driven cavity mode or into modes other than the cavity modes. Depending on the drive strength this process can happen several times. Each time there is a relative phase advance between the Zeeman sublevels. It is possible to monitor this process by measurements on the driven mode. Here we propose a scheme to manipulate the loss of amplitude of the beats (decoherence) and the beat frequency shift, by controlling the driving field and postselecting on the basis of information gathered through measurement of the cavity modes.   

Spin and motion entanglement of neutral atoms with optical frequency combs

Optical frequency combs, emitted by ultrafast modelocked pulsed lasers, are excellent tools to perform quantum coherent control. The spectral purity, large bandwidth and high pulse powers makes these sources attractive for precision control of multi-level atoms. We envisage using pairs of OFC modes to drive stimulated Raman transitions between the two hyperfine clock states of $^{87}$Rb confined on an atom chip. The Raman transitions will be driven using an all optical, four photon technique, whereby the first photon pair drives off-resonantly to the intermediate state $^{2}$S$_{1/2} \quad \vert $F=2, m$_{f}$=0$>$ and then a second photon pair resonantly drives to $^{2}$S$_{1/2} \quad \vert $F=2, m$_{f}$=+1$>$. Co-propagating Raman fields impart only a spin flip whereas non-copropagating fields transfer two photon recoil momentum to the atoms, thus entangling the internal spin with the external motion of the atoms. For site dependent control, we plan to use the high AC Stark shifts produced by the high intensity pulses.   

Coherent detection of mechanical motion with a single spin qubit

Mechanical systems can be influenced by a wide variety of extremely small forces, ranging from gravitational to optical, electrical, and magnetic. When mechanical resonators are scaled down to nanometer-scale dimensions, these forces can be harnessed to enable coupling to individual quantum systems. We present results showing that the coherent evolution of a single electronic spin associated with a Nitrogen Vacancy (NV) center in diamond can be coupled to the motion of a magnetized mechanical resonator. Specifically we use coherent manipulation of the spin to sense the driven and Brownian motion of the resonator under ambient conditions at a precision of 5 picometers. We discuss potential future applications of this technique including the detection of the zero-point fluctuations of a mechanical resonator, the realization of strong spin-phonon coupling at a single quantum level, and the implementation of quantum spin transducers.   

Probing individual environmental nuclear spins coupled to electronic spin defects with dynamical decoupling pulse sequences

Solid-state spin qubits are promising candidates for quantum computation and quantum communication applications, for which long coherence times are a prerequisite. In the case of single Nitrogen-Vacancy (NV) centers, the coherence times are often limited by interactions with the surrounding nuclear environment. In this poster we present recent experimental results demonstrating the detection of individual nuclear spins weakly coupled to single electronic spin defects beyond the ``T2-star'' limit using dynamical decoupling pulse sequences. We take advantage of the coherent nature of the hyperfine interaction to probe the nuclear environment of individual NV centers, and to identify the nearby nuclear spins and determine their coupling strengths and relative positions to the NV. We observe coupling strengths ranging from 2 MHz down to 46 kHz, well below the limit imposed by ``T2-star,'' and observe multiple nuclei coupled to a single NV. We discuss potential applications of this technique in magnetometry and quantum information science.   

Dynamics and Stability of a Superradiant Laser

We have realized a cold-atom Raman laser operating deep into the bad-cavity (or superradiant) regime, where the atomic linewidth is much narrower than the cavity linewidth. Here we present our studies on the stability of this active oscillator to external perturbations. We report on the robustness of such an oscillator when implemented in an atomic system with extra degrees of freedom beyond the simple three level model of recent theoretical proposals.   

Towards a Portable Gravimeter

In recent years, there has been increased interest in the use of atom interferometers to measure gravity with high precision and accuracy. Such a atom gravimeter can be used to measuring fundamental constants such as Newton's G and in practical applications such as geodesy and prospecting. Most atom gravimeters are designed for operation in the laboratory and not for transportation to various different environments. We present here the preliminary results of our portable atom gravimeter. Our gravimeter employs two different atomic species, namely Rb-87 and Cs-133. The use of two different species of atoms allows us increase the output bandwidth as we can make nearly simultaneous measurements of two different atomic species. This portable gravimeter will thus allow us to transport the gravimeter to a variety of environments and allow us to make measurements of gravity in situ.   

Atomic Gravitational Wave Interferometric Sensors (AGIS) in Space

Atom interferometers have the potential to make sensitive gravitational wave detectors, which would reinforce our fundamental understanding of gravity and provide a new means of observing the universe. We focus here on the AGIS-LEO proposal [1]. Gravitational waves can be observed by comparing a pair of atom interferometers separated over an extended baseline. The mission would offer a strain sensitivity that would provide access to a rich scientific region with substantial discovery potential. This band is not currently addressed with the LIGO or LISA instruments. We analyze systematic backgrounds that are relevant to the mission and discuss how they can be mitigated at the required levels. Some of these effects do not appear to have been considered previously in the context of atom interferometry, and we therefore expect that our analysis will be broadly relevant to atom interferometric precision measurements. Many of the techniques relevant to an AGIS mission can be investigated in the Stanford 10-m drop tower.\\[4pt] [1] J.M. Hogan, {\it et al.}, Gen. Rel. Grav. {\bf 43}, 1953-2009 (2011).   

Two-Mode Vacuum Squeezing of Spin-Nematic Variables in a Spin-1 Condensate

Squeezed states allow interferometers to surpass the standard quantum limit of the Heisenberg uncertainty principle. Here we study spin-nematic squeezing of a spin-1 condensate following a quench through a nematic-ferromagnetic quantum phase transition. We observe up to -8.3 dB squeezing in the variance of the spin-nematic quadratures. This squeezing is observed for negligible occupation of the squeezed modes and is analogous to optical two-mode vacuum squeezing.\footnote{C.D. Hamley, C.S. Gerving, T.M. Hoang, E.M. Bookjans, and M.S. Chapman, ``Spin-Nematic Squeezed Vacuum in a Quantum Gas,'' To appear in \emph{Nature Phys.}}   

Cavity QED with Microtoroidal Optical Resonators

Quantum control of strong interactions between a single atom and a single photon has been achieved within the setting of cavity quantum electrodynamics (cQED). To move beyond proof-of-principle experiments involving one or two conventional optical cavities to more complex scalable systems that employ many microscopic resonators requires localization of atoms on distance scales $\sim $100 nm from a resonator's surface. A single atom trapped near the surface of a fiber-coupled microtoroidal resonator provides a promising system that allows access to a new regime of cQED. Here, due to its proximity to the surface of the resonator, an atom experiences both strong 1-photon and surface interactions [1]. To advance beyond transient observations [1], we are currently working to trap single atoms within the evanescent field of a microtoroidal resonator using a single tapered fiber to provide both optical coupling and a dipole trap for the atoms [2-4]. Our goal is to realize a flexible experimental platform for investigations of small quantum networks using strong interactions of single atoms and photons. \\[4pt] [1] D. J. Alton, et al., Nature Phys. 7, 159 (2011).\\[0pt] [2] V. I. Balykin et al. Phys. Rev. Lett., 60, 2137 (1988).\\[0pt] [3] E. Vetsch et al., Phys. Rev. Lett., 104, 203603 (2010).\\[0pt] [4] C. Lacroute et al., arXiv:1110.5372.   

Sub-nanoscale Resolution for Microscopy via Coherent Population Oscillations

We present microscopy schemes to attain sub-nanoscale resolution based on two phenomena---coherent population trapping (CPT) and coherent population oscillation (CPO). The CPT based method uses three-level atoms coupled to amplitude modulated probe field and a spatially dependent drive field. Whereas, the CPO based schemes involve two-level atoms coupled to two optical fields slightly different in frequency. The modulation of the probe field (in CPT-based scheme) allows us to tap into the steep dispersion normally associated with electromagnetically induced transparency and offers an avenue to attain sub-nanometer resolution using just the optical fields. CPO-based schemes offer similar resolution as the CPT-based schemes but they are attainable in a larger class of materials. It is known that group velocity manipulations with the CPO effect have been observed in room temperature solids and biological samples as opposed to in atomic vapors and cold atomic gases in the case of CPT. This parallel allows us to extend our CPT-based work to CPO-based microscopy schemes and makes them attainable in much larger class of materials including solids and biological samples.   

Line shapes in modulation transfer spectroscopy for 87Rb atoms

We present a theoretical and experimental study of line shape in modulation transfer spectroscopy for 87Rb atoms. A linearly polarized modulated pump beam overlaps in parallel with an unmodulated linearly polarized probe beam. As a result of nonlinear interaction with atoms modulated probe beams are generated. The detected modulation transfer signals are calculated by numerically solving the complete density-matrix equations for the 87Rb atoms. We find good agreement between calculated and experimental results.   

Measurement of the Spectrum of the Down Converted Photons created in Type I SPDC

Spontaneous parametric down conversion is an important process in quantum optics, in which blue photons of a high-intensity laser beam are converted into pairs of lower energy infrared photons inside a non-linear optical crystal. Our goal is to measure the wavelength spectrum of these photons using a single photon counting module and a high resolution optical emission spectrometer. A preliminary step towards merging these two systems is to find out the minimum photon flux required to achieve an adequate signal to noise ratio with the spectrometer. Additionally, we need to determine how much signal is lost in the proposed connector between the two setups. We will present our findings from the characterization of the spectrometer, as well as dark counts from the single photon detector and measurements of the polarization properties of the down-converted photons. We will discuss how we plan to determine the wavelength spectrum of the down-converted photons.   

Slow and fast light propagation of quantum optical fields under the conditions of multi-photon resonances in a coherent atomic vapor

We investigate a weak signal pulse propagation in a $N$ interaction scheme, in which a resonant $\Lambda$ link formed by single weak signal and strong control field, traditionally associated with electromagnetically induced transparency, is perturbed by an additional optical transition. We focus on two configurations. In the first case, relevant for EIT-based slow light and quantum memory, we take into account the off-resonant coupling of the strong field to the signal field ground state. In the second configuration the additional control field is derived from an independent laser, and it is tuned to a different optical resonance from the ones forming an original $\Lambda$ system. Such interaction scheme allows was considered with regards to enhancement of optical gyroscopes performance. We demonstrate that in both cases the four-wave mixing (FWM) has a profound effect on signal field group velocity and absorption profile, and may even lead to gain. We demonstrate that in such perturbed EIT systems with FWM it may be possible to tune a signal field propagation from superluminal to slow light regimes. We present both semi-classical and fully quantum treatment for propagation of both signal and newly generated Stokes fields that include accurate description of their quantum noise.   

Ultracold Atom-Ion Schemes for Quantum Information

We present a hybrid platform for quantum information processing and quantum simulations that is based on ultracold atom-ion systems, and seeks to combine the advantages of other platforms that are already well established experimentally. By combining together the long coherence times of neutral atoms and the strong interactions of trapped ions we obtain unique properties that are not present in each of these subsystems when alone. We discuss the feasibility of these schemes for quantum information processing, as well as decoherence phenomena that will limit the effectiveness of this new platform for specific physical systems.   

Characterizing single atom optical dipole traps

Trapping and manipulating individual neutral atoms in far off-resonant traps (FORTs) is a promising approach for quantum information processing. It is important to characterize the trapping environment of the atom and the atomic level shifts due to the trapping fields. Using non-destructive measurement techniques,\footnote{M.~J.~Gibbons \textit{et al.}, \textit{Phys. Rev. Lett} \textbf{106}, 133002 (2011).} we have measured the level dependent AC Stark shifts, trap frequencies, and temperature of single rubidium atoms confined in optical dipole trap.   

Towards a field-free junction for a network of radio-frequency surface electrode ion traps

Intersections between transport guides in a network of RF ion traps are a key ingredient to many implementations of scalable quantum information processing with trapped ions. Several junction architectures demonstrated so far are limited by varying radial secular frequencies, a reduced trap depth, or a non-vanishing RF field along the transport channel. The later induces micromotion which can lead to motional heating. RF-field-free junctions have been proposed for 3D electrode geometries but cannot be easily microfabricated in a scalable way. We report on the design and progress in implementing a configurable microfabricated surface electrode Y-junction that employs switchable RF electrodes. An essentially RF-field-free pseudopotential guide between any two legs of the junction can be established by applying RF potential to a suitable pair of electrodes. The transport channel's height above the electrodes, its depth and radial curvature are constant to within 15\%.   

Suppression of spin bath dynamics for improved coherence of multi-spin-qubit systems

Scalability of multi-qubit systems is crucial for the advancement and application of quantum science. Such scalability requires maintaining long coherence times while increasing the number of qubits in the system. For solid-state spin systems, qubit coherence is closely related to fundamental questions of many-body spin dynamics. Here we apply a coherent spectroscopic technique to characterize the dynamics of the composite solid-state spin environment of Nitrogen-Vacancy (NV) color centers in room temperature diamond. We identify a new mechanism for suppression of electronic spin bath dynamics in the presence of a nuclear spin bath of sufficient concentration. This suppression enhances the efficacy of dynamical decoupling techniques, resulting in increased coherence times for multi-spin-qubit systems, thus paving the way for scalable applications in quantum information, sensing and metrology.   

Entanglement of cold molecules using strong optical pulses

We show that a strong off-resonant optical pulse can be used to create entanglement in an ensemble of polar molecules. The laser field modifies the rotational structure of molecules, enhancing the effect of the dipole-dipole interaction between molecules. This generates entanglement between molecules in different rotational states after the pulse is over. The degree of entanglement can be controlled by shaping the intensity and duration of the pulse. We show that a single nanosecond pulse can be used to produce an entangled state of molecules separated by several hundreds of nanometers, and that a sequence of pulses generate entanglement between molecules separated by tens of micrometers. We describe the possibility of using molecules trapped on an optical lattice to test Bell's inequalities by measuring orientation and alignment correlations. We also analyze the main sources of decoherence in the system and estimate the efficiency of two-qubit quantum gates for universal quantum computation with trapped polar molecules. Reference: F. Herrera, Ph.D. thesis, University of British Columbia, 2012   

Unforgeable Noise-Tolerant Quantum Tokens

The realization of devices which harness the laws of quantum mechanics represents an exciting challenge at the interface of modern technology and fundamental science. An exemplary paragon of the power of such quantum primitives is the concept of ``quantum money.'' A dishonest holder of a quantum bank-note will invariably fail in any forging attempts; indeed, under assumptions of ideal measurements and decoherence-free memories such security is guaranteed by the no-cloning theorem. In any practical situation, however, noise, decoherence and operational imperfections abound. Thus, the development of secure ``quantum money''-type primitives capable of tolerating realistic infidelities is of both practical and fundamental importance. Here, we propose a novel class of such protocols and demonstrate their tolerance to noise; moreover, we prove their rigorous security by determining tight fidelity thresholds. Our proposed protocols require only the ability to prepare, store and measure single qubit quantum memories, making their experimental realization accessible with current technologies.   

Advanced ion trap structures with integrated tools for qubit manipulation

We survey the ion trap fabrication technologies available at Sandia National Laboratories. These include four metal layers, precision backside etching, and low profile wirebonds. We demonstrate loading of ions in a variety of ion traps that utilize these technologies. Additionally, we present progress towards integration of on-board filtering with trench capacitors, photon collection via an optical cavity, and integrated microwave electrodes for localized hyperfine qubit control and magnetic field gradient quantum gates. \\[4pt] This work was supported by Sandia's Laboratory Directed Research and Development (LDRD) Program and the Intelligence Advanced Research Projects Activity (IARPA). Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.   

New approach for super-resolution imaging of NV-nanodiamonds

We describe a new approach for super-resolution imaging of nanodiamonds (NDs) containing NV centers. The random orientation of NDs in a static magnetic field allow each ND to be distinguished by the NV ESR Zeeman shift and spin-state-dependent fluorescence rate. We exploit this behavior as a photo-switch such that adjacent NDs emit fluorescence sequentially in time. Post-analysis of a series of images at each ESR resonance frequency can localize individual NDs with sub-wavelength resolution. This technique has the advantage of being compatible with CCD-based wide-field microscopy, and involves significantly less laser intensity and experimental complexity than STED-based approaches.   

A Quantum Optics Toolbox for Polyatomic Molecules

We present a combination of techniques to manipulate the external and internal degrees of freedom of polyatomic molecules. A novel microstructured electric trap\footnote{M. Zeppenfeld {\it et al.}, Phys. Rev. A {\bf 80}, 041401 (2009)}$^,$\footnote{B.G.U. Englert {\it et al.}, Phys. Rev. Lett {\bf 107}, 263003 (2011)} provides ideal motional control for polar molecules, generating a box-like potential with tuneable homogeneous electric fields over a large fraction of the trap volume and high trapping fields only near the trap boundary. The combination with radiation fields to manipulate the internal degrees of freedom allows full control of the molecules. Specifically, microwave and RF fields couple rotational states. Vibrational excitation via an infrared laser provides a dissipative spontaneous decay. The homogeneous fields inside the trap allow individual states to be selectively addressed. As first applications, we have realized adiabatic cooling\footnote{Ibid.} and opto-electrical cooling.\footnote{Zeppenfeld, op. sit.} Further improvements will allow fundamental experiments with a wide range of polyatomic molecules at ultracold temperatures.   

Rydberg atoms in a linear magnetic atom guide

We study the trapping and guiding of Rydberg atoms in a high-gradient two-wire magnetic atom guide. Samples of several hundred cold 59D$_{5/2}$ Rb Rydberg atoms are prepared at densities of order 2x10$^8$~cm$^{-3}$. The atoms are ionized after a variable delay time using a microwave pulse. The resulting ions are imaged onto a position-sensitive microchannel plate detector, and time-domain multi-scaler traces as well as gated CCD images of the ion signals are obtained. We observe guiding of Rydberg atoms over a period of 5~ms following excitation. There is a brief initial period during which about 7$\%$ of the Rydberg atoms undergo Penning ionization. The decay time of the guided atom signal is about five times that of the initial state lifetime. We attribute the increase in lifetime to an initial phase of l-changing collisions concurrent with the Penning ionization phase and also to thermal electric-dipole transitions. A Monte Carlo simulation reproduces most experimental observations and offers insight into the internal-state dynamics.   

Few-body phenomena in ultracold cesium: More resonances, more bodies, and less dimensions

Efimov trimers represent the paradigm of universal few-body physics and they have been subject to manifold investigations [1]. An important quantity, both for theory and experiments, is the so-called three-body parameter, which fixes the positions of the Efimov resonances. Our measurements with ultracold cesium are consistent with a constant three-body parameter, even when different Feshbach resonances are involved for the tuning of the scattering length [2]. Furthermore, the wide tuning range allows us to explore a series of N-body states by observing four- and five-body recombination resonances [3]. In ongoing experiments, we investigate how few-body states behave when a dimensional confinement is applied, from a shallow three-dimensional trap to a quasi two-dimensional situation. Preliminary results show that the position of the Efimov resonance shows a pronounced shift to lower absolute values of the scattering length. \\[4pt] [1] F. Ferlaino et al., Few-Body Syst. 51, 113 (2011)\\[0pt] [2] M. Berninger et al., Phys. Rev. Lett. 107, 120401 (2011)\\[0pt] [3] J. von Stecher, Phys. Rev. Lett. 107, 200402 (2011)   

Developing Density for Collisional Experiments with Ultracold Molecules Using a Magnetic Injector/Accumulator

A prerequisite to studying ultracold chemistry is achieving a sufficient collision frequency as facilitated by creating a high number density. In this poster we show that some of the basic concepts and components of particle injectors and accumulators used in accelerators can be exploited to generate dense ensembles of ultracold magnetic particles, including laser-cooled paramagnetic atoms \textit{and} molecules. For example, particles will be injected in one magnetic state and stored in another, much like charge-exchange injection into accelerator storage rings, allowing the progressive growth in density. We test these concepts first with atoms in preparation for later work with molecules. Presently, the injector stage uses a magnetic field and optical pumping to switch the state and trajectory of laser-cooled atoms into the stored state and accumulator path. Particle tracking calculations, design, and experiments with the injection and accumulation of 7Li will be presented. Finally, we will present our preliminary results in laser cooling of CaH and efforts to implement an injector/accumulator for these ultracold molecules.   

Imaging spatial correlations of Rydberg excitations in cold atom clouds

We measure correlations between excitation positions in cold Rydberg gases. We have previously observed\footnotemark[2] Rydberg-blockade-induced structures in the Rydberg pair correlation function similar to those predicted in.\footnotemark[3] Here, we study the effect of Coulomb repulsion after field ionization, which could possibly influence the pair correlation measurement. We have simulated the ion trajectories in our chamber and determined that Coulomb repulsion did not play a role in any of our previous experiments. However, with higher magnification we expect to observe this effect as well. In the experiment, we already have obtained a magnification increase by about a factor of two, and progress towards even higher magnification is still being made. We will report on our progress in imaging smaller structures in the pair correlation function, induced by Coulomb repulsion and possibly by adiabatic Rydberg crystal formation.\footnotemark[4] \footnotetext[2]{A. Schwarzkopf et al. Phys. Rev. Lett. 107, no. 10 (2011): 103001.} \footnotetext[3]{F. Robicheaux and J. Hernandez. Phys. Rev. {\bf A 72}, 63403, 1-4 (2005).} \footnotetext[4]{T. Pohl et al. Phys. Rev. Lett. 104, no. 4 (January 27, 2010): 043002.}   

Beyond mean-field effects in Bloch Oscillations of cold atoms in an optical cavity

In our earlier publication [1] we proposed using Bloch oscillations of cold atoms inside an Fabry-Perot resonator for sensitive measurements of force. The analysis in [1] was performed using a coherent mean-field description for the atoms and the light. In the current work we extend this description substantially by including the effects of fluctuations in both the atomic and light fields. This analysis is used to set realistic limits on the precision to which the force can be measured. We also make contact with the optomechanical description of the combined atom-cavity system which has proved so successful for describing recent pioneering experiments [2].\\[4pt] [1] B. Prasanna Venkatesh et al, Phys. Rev. A 80, 063834 (2009).\\[0pt] [2] S. Gupta et al, Phys. Rev. Lett. 99, 213601 (2007); F.Brennecke et al, Science 322, 235 (2008).   

Photon mediated transport and crystallization in optically driven Rydberg gases

We show that excitations in a gas of atoms driven to Rydberg states by near-resonant laser radiation in a two-photon coupling scheme experience a photon mediated transport. Thus even if the center-of-mass motion of the atoms can be neglected, this results in a kinetic Hamiltonian for the Rydberg excitations. The corresponding mass is identical to that of the dark-state polaritons of the optical coupling scheme. The kinetic energy competes with the Rydberg dipole-dipole interactions and can prevent the formation of quasi-crystal structures. Using DMRG simulations we calculate the Luttinger parameter for a one-dimensional gas of resonantly driven Rydberg atoms taking into account the photon mediated transport and derive conditions under which quasi-crystallization can be observed.   

Non-Zero Temperature analysis of a quasi2D dipolar gas

We present non-zero Temperature analysis of a quasi2D dipolar gas. To do this, we use the Hartree Fock Bogoliubov (HFB) method within the Popov approximation. This formalism is a set of non-local equations containing the dipole-dipole interaction and the condensate and thermal correlation functions, which are solved self-consistently. We detail the numerical method used to implement the scheme. We present density profiles for a non-zero temperature dipolar gas in q2D, and compare these results to a gas with zero-range interactions. Additionally, we analyze the excitation spectrum.   

Synthetic partial waves in ultracold atomic collisions

Interactions between particles can be strongly modified by their environment. We describe an experimental technique for modifying interactions between ultracold atoms by screening the native interaction with light, significantly increasing the range of the interaction and allowing coupling of states of higher angular momentum. We study collisions between Bose-Einstein condensates dressed by counter-propagating Raman beams, where the eigenstates of the Raman-dressed system are spin-momentum superpositions. Collisions between bosons at the low temperatures associated with quantum degeneracy are usually well-described by a purely isotropic (s-wave) interaction. In contrast we observed effective higher order (beyond s-wave) partial wave interactions between colliding BECs in the ground Raman dressed state at collision velocities orders of magnitude below those traditionally required to surpass the s-wave scattering regime. Furthermore we investigate scattering in excited Raman-dressed states and observe collision-induced decay to lower energy Raman-dressed states which can be p-wave or d-wave in character.   

Towards a $^{87}$Rb BEC apparatus with reconfigurable arbitrary optical potentials and artificial gauge fields

We have constructed an all-optical $^{87}$Rb BEC apparatus, which is currently creating condensates in a 1550nm cross beam optical dipole trap every 30s. We present experimental progress toward implementing reconfigurable arbitrary optical potentials and artificial gauge fields in our apparatus. Time-averaged, dynamically-reconfigurable, arbitrary-shaped optical potentials are generated using a dual-axis AOM controlled by a two-channel high-bandwidth arbitrary RF waveform generator. Using a blue-detuned 532nm laser, we have demonstrated various optical potential geometries such as a tilting wedge, checkerboard and elliptical barriers. Such arbitrary, reconfigurable optical potentials will be used to explore quantum phase transitions in superfluids. Our excellent optical access also allows the addition of Raman beams of various arrangements. Raman dressed states can be used to induce spin dependent artificial gauge fields for studying physics such as the spin Hall effect.   

Collective excitations in quasi-2D Condensates

In lower-dimensional gases, remarkable physical phenomena arise due to confinement effects, for example the Berezinskii-Kosterlitz-Thouless transition or the Tonks-Girardeau gas. In a quasi-2D condensate, the frequency of collective excitations are shifted because of 2D effects [1,2]. We report our latest results on the measurements of collective excitation frequencies in quasi-2D condensates. These frequencies are normalized by precise measurements of the trapping frequency. \\[4pt] [1] Y. Hu et al., Phys. Rev. Lett. 107, 110401 (2011).\\[0pt] [2] M. Olshanii et al., Phys. Rev. Lett. 105, 095302 (2010).   

Quantum Degenerate Gases in an All-Optical Toroidal Trap

Quantum degenerate gases confined in a toroidal potential show persistent currents, azimuthal sound waves, and other transport phenomena related to coherent, unrestricted flow around the waveguide. Sound waves and vortex states in a ring can be used to for accurate, absolute rotation sensing. We report on the status of our all-optical toroidal trap for Bose-condensed $^{87}$Rb. We discuss techniques to generate angular momentum and unusual spin structures as well as future prospects with spinor gases and quantum degenerate lithium.   

Three-fermion system with $s$-wave interactions under anisotropic harmonic confinement

We develop an efficient numerical approach to solve the Schr\"odinger equation for three fermions in two different spin states with zero-range $s$-wave interactions under cylindrical harmonic confinement. Our approach builds on the work done for isotropic confinement [1] and is applicable to traps with integer aspect ratio. We reproduce the known results for the aspect ratio of unity and analyze the energy spectrum when the aspect ratio is different from one. In the weakly-interacting regime our results agree with perturbative calculations. The eigenenergies are used to calculate the third-order virial coefficient as functions of the aspect ratio, temperature and $s$-wave scattering length.\\[4pt] [1] J. P. Kestner and L.-M. Duan, Phys. Rev. A. 76, 033611 (2007).   

Hyperspherical explicitly correlated Gaussian approach for four-body systems with finite angular momentum

It has been predicted that four-body systems with angular momentum $L=1$ and parity $\pi=+1$ exhibit four-body resonances [1,2] and Efimov physics [3]. To treat these phenomena in the hyperspherical framework, we extend the work of von Stecher and Greene [4] to finite angular momenta. In particular, we employ explicitly correlated Gaussian basis functions with global vectors to solve the hyperangular Schr\"odinger equation for four-body systems with $L^{\pi}=1^+$ and $1^-$ symmetry. We apply the approach to four-fermion systems with unequal masses.\\[4pt] [1] K. M. Daily and D. Blume, Phys. Rev. Lett. 105, 170403 (2010).\\[0pt] [2] S. Gandolfi and J. Carlson, arXiv: 1006.5186v1.\\[0pt] [3] Y. Castin, C. Mora and L. Pricoupenko, Phys. Rev. Lett. 105, 223201 (2010).\\[0pt] [4] J. von Stecher and C. H. Greene, Phys. Rev. A. 80, 022504 (2009).   

Quasi-one-dimensional scattering in a discrete model

We present quasi-one-dimensional scattering of one and two particles with short-range interactions on a discrete lattice model in two dimensions. One of the directions is tightly confined by an arbitrary trapping potential. In the case of two-particle scattering, we will show that more than one confinement-induced resonance appear due to the non-separability of the center-of-mass and relative coordinates on the lattice, which is a necessary ingredient in any experimentally relevant situation.   

Spatially Selective Imaging in a Three-Dimensional Optical Lattice

We have developed a technique to isolate atoms at the center of a three-dimensional optical lattice. A microwave-frequency magnetic field is used to transfer the central atoms into a hyperfine state that is selectively imaged. The center is spectroscopically resolved using hyperfine-state-sensitive AC Stark shifts effected by crossed laser beams. We discuss how this technique may be applied to compressibility measurements to aid in the determination of the three-dimensional disordered Bose-Hubbard phase diagram.   

Adiabatic loading and cooling of SU(N) alkaline earth atoms in optical lattices

We present thermodynamic properties of SU(N) alkaline earth atoms adiabatically loaded onto optical lattices. In particular, we compute the final temperatures obtained by such a procedure and identify an enhanced cooling effect when increasing N. The combination of high temperature series expansion and extensive numerical calculations (Quantum Monte Carlo and DMRG) allows us to characterize this effect over a wide range of initial temperatures and to identify the temperature regime in which the physics is governed by SU(N) superexchange interactions. We discuss implications for ongoing experiments.   

States of one and two atoms in a rotating ring lattice

We study the states of one and two bosonic atoms in a rotating ring lattice using a Hubbard type model, including phases on the tunneling matrix elements that depend on the rotation speed. The combination of the topology of the ring and the twisting boundary conditions of the wave functions due to the rotation leads to a rich phenomenology and novel methods to control the atoms in the lattice. For instance, the physics qualitatively depends on the parity of the number of lattice sites, and one can tailor the preparation of both one-atom and lattice dimer states by varying the rotation speed.   

A state-insensitive nanofiber trap

The development of quantum interface using cold atoms and optical fibers has been an active field of research. Following the pioneering work of Balykin et al [1] and Vetsch et al. [2], we realize trapping cesium atoms using a state-insensitive evanescent wave around a nanofiber [3]. By using the magic wavelengths, we remove the differential scalar light shift between the ground and excited states. The vector light shift induced by a forward-propagating wave is canceled by a backward-propagating wave. We measure the transmission spectrum of 200 trapped atoms, and obtain a resonant optical depth of 15 at a storage time of 1.5 ms, decaying to an optical depth of 1.0 after 300ms. The state-insensitivity is demonstrated by the measured linewidth of 5.6 MHz, similar to the natural linewidth of 5.2 MHz in free space. Our scheme provides a promising approach to trap and probe neutral atoms in a nanofiber trap with long coherence lifetimes using realistic parameters. [1] V. I. Balykin et al. Phys. Rev. Lett., 60, 2137 (1988). [2] E. Vetsch et al., Phys. Rev. Lett., 104, 203603 (2010). [3] C. Lacroute et al., arXiv:1110.5372.   

Progress towards a Fermi Gas Microscope

Attractively interacting degenerate Fermi gases near a Feshbach resonance have been used to realize the BEC-BCS crossover, while repulsive gases in optical lattices are expected to shed light on the physics of high-temperature superconductors. Local probes of these atomic systems should reveal microscopic correlations in such strongly interacting systems that cannot be directly extracted from bulk measurements. With the advent of quantum gas microscopy, the potential of such local probes has been demonstrated in bosonic gases. We are developing an experimental apparatus that combines quantum gas microscopy techniques with ultracold fermions in optical lattices to simulate strongly-correlated electronic systems. Our apparatus is designed to create degenerate gases of fermionic lithium and potassium as well as bosonic sodium. The gases will be loaded into a single layer of an optical lattice and imaged with a sub-micron resolution optical system capable of resolving individual sites. Our system opens the door to microscopic studies of phases that appear in the Fermi-Hubbard model including fermionic Mott insulators, antiferromagnets and d-wave superfluids, as well as topological phases that arise in the presence of synthetic gauge fields.   

Dynamics of matter waves in tailored optical and atomic lattices

We report experimental results on the dynamics of atomic matter waves in temporally and spatially modulated lattices. In a first experiment, we investigated the effects of disorder on dynamical localization in a periodically-pulsed optical lattice in the framework of a kicked-rotor model. A second experiment explored the interplay between disorder and interactions in the damping of Bloch oscillations in a tilted disordered lattice. In a third experiment, we examined the diffraction of atomic matter waves from 1D ``crystal'' arrays of lattice-trapped atoms with respect to the temporal dynamics of matter-wave scattering. We also demonstrated the use of matter waves to detect forced antiferromagnetic ordering in an atomic spin-mixture.   

Orbital Excitation Blockade and Algorithmic Cooling of Strongly Correlated Quantum Gas

Ultracold quantum gases in optical lattices provide a rich experimental toolbox for simulating the physics of condensed matter systems. Here we present a new blockade effect that employs the orbital dependence of the interaction between bosons in optical lattices to manipulate the onsite occupation in a strongly interacting quantum gas. We induce coherent orbital excitations by modulating the lattice depth and observe interaction-induced energy shifts in the modulation resonances. By sweeping the modulation frequency across several resonances we can deterministically remove atoms on individual sites based upon initial occupation. Using this number filtering approach, we have demonstrated algorithmic entropy removal from a high-temperature gas to the point that it Bose-condenses. This algorithmic cooling can be used to bring quantum gases to the pico-Kelvin regime required for observing strong correlations. Further applications of these methods include preparation of high fidelity quantum registers, imaging strongly-correlated quantum gases, and generation of entangled orbital states.   

Single Mode Quantum Pumps using Wavepackets of Bose-Einstein Condensates

Quantum pumps generate transport by time-varying potentials but implementation in mesoscopic systems has remained elusive despite much interest. We apply a novel approach using counter-propagating wavepackets [1] to study this quantum transport mechanism at the single mode level. This allows us to probe features not accessible with standard methods of mesoscopic physics: We examine the rich momentum distributions resulting from quantum pumps in different configurations, including a new one that operates like a ``quantum paddlewheel.'' We find that with dual periods, the momenta present a Floquet structure that interweaves both. Our simulations easily translate to experiments with Bose-Einstein Condensates in waveguides, being currently developed. One of the key advantages of our simulations, as well as related experiments, is that we can examine the effects of nonlinearity on quantum pumps. Despite the intrinsic spatial non-uniformity of wavepackets, we show that convergent results for nonlinear transport are obtained as packet widths are increased, provided that the peak density is kept constant. Our basic approach can be generalized to study most mesoscopic transport phenomena with ultracold atoms.\\[4pt] [1] Kunal K. Das, Phys. Rev. A 84, 031601(R)   

Reservoir induced criticality in 1D bosonic lattice systems

We discuss reservoir driven phase transitions to critical states in one-dimensional bosonic lattice systems subject to local dissipation. By coupling to local reservoirs fermionic and bosonic lattice systems can be driven to a steady state which shows criticality in the sense of a diverging correlation length. For free lattice bosons this criticality is generically associated with a dynamical instability of the system. To avoid this instability we introduce a nonlinearity by saturating the dissipative gain. We consider coupling of the lattice sites to common local reservoirs of different range and derive correlations as well as critical exponents of the induced quasi-phase transition in a mean-field approximation.   

Non-equilibrium physics of spinor quantum fluids

We are working towards a multispecies ultracold atom apparatus intended for studies of non-equilibrium physics of quantum degenerate spinor fluids. These studies rely on the ability to generate large spatially extended ensembles of ultracold gases. In addition, quantitative studies of the non-equilibrium dynamics require the development of techniques for time-resolved nondestructive images of these gases. We report on experimental progress towards both these goals. We complement these experimental efforts with theoretical studies of spinor gases in non-equilibrium scenarios. In particular, we present results on a dynamical Kosterlitz-Thouless transition in quasi-2D F=1 spinor gases.   

Construction of a Dye Laser for Use in Detecting Ultracold RbCa

Ultracold heteronuclear molecules have seen increasing interest in the scientific community over the last few years. By controlling their ro-vibrational energy levels, ultracold molecules can be used for high precision spectroscopy, to study cold collisions with rich internal dynamics, as model systems for condensed matter physics, and as qubits in quantum information processing. We study the novel combination RbCa. In addition to a permanent electric dipole moment, it also possesses a permanent magnetic dipole moment. This makes it an ideal candidate to study strong long-range dipole-dipole interactions. A dye laser system will be used to ionize RbCa through resonantly enhanced multi-photon ionization (REMPI). We use a Nd:YAG pulsed laser to pump a dye solution in a quartz glass cell. The linewidth of the dye laser is narrowed through use of a diffraction grating in Littman-Metcalf configuration. We have performed \textit{ab initio} calculations to calculate the electronic energy levels of RbCa, and Franck-Condon factors to determine the best wavelength for REMPI. These data will be used to optimize further calculations of molecular energy levels.   

Quasi-resonant transitions in ultracold collisions of hydrogen isotope dimers: zero-energy resonances in vibration space

The quasi-resonant rotation-rotation (QRRR) mechanism is studied theoretically in ultracold H$_2$, D$_2$, and HD self-collisions as a function of initial vibrational level $v$. In the QRRR mechanism, the collision partners swap internal rotational excitation resulting in large cross sections and scattering lengths. The efficiency of the QRRR mechanism is a consequence of conservation of total system internal rotational angular momentum and near conservation of internal energy. Extending to high vibrational excitation, we find that the QRRR mechanism identified for H$_2$($v=1$)+H$_2$($v'=0$) by Qu\'em\'ener {\it et al.} [1] persists with scattering lengths, both real and imaginary, varying smoothly with $v$. However, exceptions occur at select high values of $v$ where the scattering lengths are enhanced by orders of magnitude corresponding to the location of a zero-energy resonance in ``vibration space." Similar trends are seen for D$_2$ and HD self-collisions. If the QRRR mechanism operates in other ultracold dimer-dimer collision systems, then vibrational excitation may be used to ``tune" the interaction strength similar to methods which use external fields or theoretical variation of the reduced mass.\\[4pt] [1] G. Qu\'em\'ener et al., {\it Phys. Rev.} A {\bf 77}, 030704(R) (2008).   

Using Feshbach-optimized photoassociation spectroscopy to determine potential energies for excited electronic states of dimers

Many experiments on ultracold ($<1\,$mK) gases use magnetic-field-induced Feshbach resonances to enhance photoassociation (PA)~[1]. A magnetic field applied to a sample of trapped ultracold atoms induces a Feshbach scattering resonance that can increase the PA rate into bound excited molecular states. We are studying how to use Feshbach resonances in PA spectroscopy~[2] to determine accurate excited-state Born-Oppenheimer potential energies. For ${}^{85}$Rb$_2$ we present calculated resonance properties and energies for excited vibrational states that are inaccessible with conventional PA spectroscopy. \\[4pt] [1] Chin et al., Rev. Mod. Phys. \textbf{82}, 1225~(2010).\\[0pt] [2] Pellegrini et al., Phys. Rev. Lett. \textbf{101}, 053201~(2008).   

Apparatus to image ultra-cold impurities in Bose-Einstein condensates

We present an experimental apparatus with enhanced ion imaging capabilities relative to our previously used set-ups. The apparatus will be employed to study interactions between ultra-cold impurities and Bose-Einstein condensates (BEC). Atoms will first be loaded into a primary Magneto-optical trap (MOT), which loads a secondary MOT, and then into a quadrupole-Ioffe-configuration (QUIC) trap, where a BEC is formed. Free ultra-cold ions will be made by photoionizing a few atoms. Stray electric fields are canceled by an electrode package surrounding the BEC-ion interaction region. The electric field of a sharp needle (tip diameter 125 microns) is used to generate highly magnified ion images. In our poster, we will discuss expected phenomena, which include quantum charge diffusion [R. Cote, E. Bodo, P. Zhang, and A. Dalgarno], mesoscopic molecular ion formation [R. Cote, V. Kharchenko, and M.D. Lukin, Massignan, C.J. Pethick, and H. Smith], ion self-trapping [R.M. Kalas and D. Blume], and ultra-cold plasma expansion (in the classical domain). We will show details of the experimental apparatus, which is in its final assembly stage.   

Progress towards creating and manipulating ultracold LiRb molecules

We present our progress towards creating ultracold LiRb molecules from a dual species magneto-optical trap (MOT) of $^{7}$Li and $^{85}$Rb. We suggest photoassociation (PA) pathways for efficient production of ultracold LiRb molecules based on our recent experimental work on spectroscopy of LiRb molecules (S. Dutta et al., Chem. Phys. Lett. 511, 7 (2011)). We discuss a scheme based on interference of optical transitions to create ultracold molecules in a superposition of rotational states, and their manipulation based on an optical-phase based coherent control technique. We describe our apparatus where ultracold LiRb molecules will be created using PA, oriented using optical-phase based coherent control, and then detected using multiphoton ionization. We also discuss the ability of our apparatus to image the orientation of such molecules.   

Investigation of photoassociative transitions in NaCs detuned from the Cs D1 line

We utilize photoassociation (PA) to form bound NaCs molecules in excited states detuned from the Cs $6^2P_{1/2}$ dissociation asymptote. The PA structure consists primarily of levels belonging to the $A^1\Sigma^+$, $b^3\Pi_{\Omega=0^+}$, $b^1\Pi$, and $b^3\Pi_{\Omega=2}$ electronic states. All of these but the $A^1\Sigma^+$ electronic state dissociate to the Cs $6^2P_{3/2}$ asymptote, indicating that free-bound excitation occurs even to deeply bound vibrational levels. We find that mixing between electronic states and an \textit{f}-wave shape resonance enhances the free-bound transition moments. We infer properties of the scattering wave from the PA spectra, and investigate the populated ground states using photoionization and depletion spectroscopy.   

High power rapidly tunable system for laser cooling

Laser cooling experiments require light sources that can be rapidly tuned in frequency and power. Keeping as much power as possible increases the number of trapped atoms. We present a configuration that combines the capabilities of rapid frequency tuning with power amplification in a robust system. A double pass acousto-optic modulator (AOM) changes the frequency of the laser beam while keeping the alignment approximately constant. We decouple the modulation and amplification sections using an optical fiber and we keep the power out of the fiber constant by feed-forward on the amplitude modulation of the AOM. The tapered amplifier is in a double pass configuration and requires an input of only 1 mW to obtain 1 W out. A second modulator controls the intensity after the amplifier and generates additional beams that we use, for example, to do absorption imaging. We demonstrate the transfer of atoms to a dipole trap using the system.   

System for Trapping Cold Neutral Atoms Around an Optical Nanofiber

We have constructed a robust system for studying atom-light interactions in atomtronics and hybrid quantum information. We require the loading of atomic dipole traps formed on tapered optical nanofibers and other photonic structures from magneto-optical traps. A commercially available UHV manipulator allows for controlled translation of the structures into the chamber with the trap while reducing the turn-around time to obtain ultra-high vacuum. The translation and pump out protocols require care not to destroy or contaminate the fibers and other photonic structures. We can, for example, translate a 500 nm diameter, 2 cm length optical nanofiber to the center of a $^{87}$Rb cloud and load cold atoms into the evanescent field around the nanofiber. We also present experimental proposals to use the nanofiber trap as a microwave-to-optical photon transducer and as part of a stable atomic memory in a hybrid quantum processor that combines atoms and circuit-QED.   

Analysis of a state-insensitive, compensated nanofiber trap

Laser trapping and interfacing of laser-cooled atoms in optical fiber networks is an important capability for quantum information science. Following the work of [1] and [2], we propose a method of trapping single Cesium atoms with a two-color, state-insensitive evanescent wave near a dielectric nanofiber. The vector light shifts induced by the ellipticity of the forward-propagating wave can be canceled by a backward-propagating wave. By operating the trap at magic wavelengths, we remove the differential scalar light shift between ground and excited states, allowing for resonant driving of the optical D2 transition. Tensor shifts are inherent to the D2 excited state 6P3/2, but vanish for the D1 excited state 6P1/2. We show that the proposed scheme of [3] can be translated to the Cs D1 line, reducing further the excited state splitting. These properties will enable quantum-state engineering in optical traps near microscopic optical waveguides and resonators, including for implementations of quantum memories, coupling of single atoms and ensembles to optical and mechanical resonators, and studying 1-D spin chains. [1] Balykin et al, PRA, 70(1):011401, 2004. [2] Vetsch et al, PRL, 104(20):203603, 2010. [3] Lacroute et al, New J. Phys. (in press); arXiv:1110.5372v1.   

Design and Construction of a Dual Anti-Helmholtz Magnet System for a Side-by-Side MOT

The design of a cold-atom interferometric gradient magnetometer [1] requires two side-by-side identical atom clouds separated by approximately 1 cm for noise reduction purposes. The first step in building this system is a side-by-side MOT to capture the atoms; however, the design of a coil system to provide two zero field crossings with high field gradients separated by a small distance with low power consumption can be challenging. These three requirements are not easy to satisfy simultaneously, but there is a large ``state space'' in which we can evolve different designs. In this poster we analyze the requirements for such a system and discuss our design consisting of coils with wires wrapped on a truncated cone; this type of design has been made possible by recent advances in 3D printers, and we will go over the issues involved in printing the coil supports, building the coils and comparison of our measurements of the magnetic field to theory. We also discuss the possibility of optimizing coil design using state space searches like the Metropolis algorithm, and how these designs can be realized using 3D printing technology. \\[4pt] [1] Davis, J. P. and Narducci, F. A.(2008) ``A proposal for a gradient magnetometer atom interferometer,'' Journal of Modern Optics,55:19,3173 --- 3185   

Vacuum Pressure Measurements using a Magneto-Optical Trap

We demonstrate that the loading dynamics of an alkali-atom magneto-optical trap (MOT) can be used as a reliable measure of vacuum pressure. This technique could be useful when a conventional pressure gauge is unavailable due to constraints on the vacuum system design. We find that for a MOT loading time $\tau$, the vacuum pressure can be estimated as ($2\times 10^{-8}$ Torr s)/$\tau$. This relation is accurate to within approximately a factor of two over wide variations in trap parameters, background gas composition, and trapped alkali species. At low pressures, the accuracy of the method is limited by losses from two-body elastic collisions within the trap. The loss rate from these collisions varies with the MOT parameters, but typically the method can extend into the $10^{-10}$ Torr range. We will present theoretical and experimental verification of the technique, based on both our own investigations and previous reports in the literature.   

Coupling of ions to superconducting circuits

We present experimental progress towards coupling the motion of ion strings to the resonant mode of a superconducting high-quality tank circuit. We consider such a coupling as the first step towards interfacing trapped ions with superconducting qubits. In our demonstration experiment, we aim to reduce the temperature of the resonant mode of the tank circuit by extracting energy from the circuit via laser cooling an ion string. One of the main experimental challenges is to construct a tank circuit with such a high quality factor Q that the ion-resonator coupling exceeds the environment-resonator coupling. Currently, we achieve Q = $27\;000$ at a frequency of $\omega=2\pi\cdot1.2\;\rm{MHz}$. For this mode, the coupling time-scale to the environment is on the order of 50~Hz. We plan to use a trap with an ion-electrode distance on the order of $100\;\rm{\mu m}$ resulting in an ion-resonator coupling of 1$\; $kHz. This coupling should reduce the electronic temperature of the resonant mode by two orders of magnitude as compared to the ambient temperature. The Q of higher order resonant modes of our resonator reach the $10^5$ regime. We will discuss limitations of the observed Q as well as improvements on the design such as trapping closer to the electrodes.   

A Quasi-Electrostatic Trap for Rubidium-87 atoms

We will discuss our system used for trapping and cooling atoms with a single focused CO$_2$ laser beam. Atoms are transferred to this quasi-electrostatic trap (QUEST) from a compressed MOT (CMOT) where they are cooled through evaporation. We will describe how to optimize the CMOT to maximize the phase space density in the QUEST. We will also present a calculation that contrasts the dynamics of free evaporation in our single beam optical trap with evaporation in a truncated parabolic potential that describes a magnetic trap.   

Kinetic phenomena in electron transport in non-equilibrium plasmas sustained by radiofrequency electric and magnetic fields

Future generation plasma discharge technologies require an accurate knowledge of the transport properties of charged particles in gases under the influence of electric and magnetic fields. In this work, the non-equilibrium transport of electrons in gases under the influence of radio-frequency electric (\textbf{E}) and magnetic (\textbf{B}) fields is studied via a unified time-dependent multi term solution of Boltzmann's equation. We systematically investigate the explicit effects associated with the \textbf{E} and \textbf{B} fields including field to density ratios, field frequency to density ratio, field phases and field orientations. In particular, we highlight the duality of transport coefficients induced by the explicit and implicit effects of non-conservative collisional processes of attachment and ionization. A multitude of kinetic phenomena are observed that are generally unpredictable through the use of steady-state dc transport theory. Phenomena of significant note include the existence of transient negative diffusivity, time-resolved negative differential conductivity and anomalous anisotropic behavior of longitudinal and transverse diffusion coefficient along the \textbf{E}$\times $\textbf{B} direction.   

Electrostatic electron oscillations and damping in an ultracold plasma

We study various collective oscillations in ultracold plasmas by driving the oscillations with an applied rf field and measuring the current induced on a nearby electrode. Previously we made measurements of a zero-temperature edge-mode and confirmed the importance of the changing plasma neutrality in determining the resonant frequency. We present an equivalent circuit model for the plasma that is capable of reproducing the main features of the induced current signals that we observe. We attempt to use the model to measure the damping of the oscillation and how it changes with electron temperature. We also show results from driving cold plasma oscillations at an arbitrary angle to a uniform magnetic field, where we find a series of modes roughly consistent with upper hybrid oscillations and a series of modes at very low frequencies ($< 1$ MHz) that as yet are unidentified. This work is supported by the NSF.   

Atomic Parity Non Conservation with Francium atoms in the FrPNC collaboration

The FrPNC collaboration is dedicated to the study of the nuclear weak interaction through measurements of Parity Violation in francium atoms. We are preparing to measure both the nuclear spin independent part of the interaction that results in the determination of the weak charge and the nuclear spin dependent part dominated by the anapole moment. The experiment has moved to TRIUMF in a room carefully shielded from RF noise. The Fr production at TRIUMF is on the isotope range of A=203-229 with yields up to 10$^{8}$ s$^{-1}$, giving us access to both the neutron deficient and rich sides. An ion optics system at the end of the beam line delivers the Fr ions to the neutralizer. The trapping side has been successfully tested with rubidium. The complete system delivers cold and trapped atomic Fr in a robust way to the science chamber where the measurements will take place.   

Precise measurement of the $7P_{1/2}$-state hyperfine splittings and isotope shift in $^{203}$Tl and $^{205}$Tl

We have undertaken a series of high-precision atomic structure measurements in thallium to test ongoing \emph{ab initio} atomic structure calculations of relevance to various symmetry violation tests in this particular element. Currently we are using a two-color, two-step spectroscopy scheme to measure of $7P_{1/2}$ hyperfine structure and isotope shift using a heated quartz thallium vapor cell. Our group recently completed a similar experiment in indium.\footnote{M.Gunawardena \emph{et al.}, Phys. Rev. A 80, 032519 (2009)} Here, one laser, locked near the thallium $6P_{1/2}\rightarrow7S_{1/2}$ 378 nm transition excites both naturally-occurring isotopes to an intermediate state. A second laser at 1301 nm overlaps the UV beam within the thallium vapor cell in both a co-propagating and counter-propagating configuration. Analysis of subsequent IR absorption spectra as we scan across the $7S_{1/2}\rightarrow7P_{1/2}$ transition allows us to extract both hyperfine and isotope shift information for this excited state. Frequency modulation of the IR laser provides convenient \emph{in situ} calibration method for the measured splittings. Our goal is to determine the thallium splittings with an accuracy of 0.1 MHz. Current results will be presented.   

Shifts from distant neighboring levels in high-precision microwave spectroscopy of the $n=2$ triplet helium fine structure

In previous work, the systematic shifts of a resonance due to quantum interference from a distant neighboring resonance were derived for a closed four-level system [1]. Here we consider $n=2$ triplet helium fine structure transitions in the microwave regime which are of interest for more accurate determinations of the fine-structure constant. The shifts are evaluated for both the Ramsey method of separated oscillatory fields (SOF) and for single microwave pulses driving the $2^3 P$ intervals. The shifts are obtained by solving density matrix equations numerically, with the system initially prepared in the $2^3P_1, m_J=0$ state and driven, e.g., near-resonantly to the $2^3P_2, m_J=0$ state by 2.29-GHz microwaves. Despite being far off resonance, the $2^3P_0, m_J=0$ state (which is 29.6 GHz away) has a non-zero excitation probability and interference from the spontaneous radiation from from the two states causes a small shift in the line center for the measured interval. The magnitude of such shifts are determined for measurements of both the 2.29-GHz and 29.6-GHz intervals. The SOF shifts are found to be considerably smaller than the single-pulse shifts. \\[4pt] [1] M. Horbatsch, E.A. Hessels, Phys. Rev. A 84, 032508 (2011)   

Efficient detection of $2^3S_1 m=0$ states of atomic helium for improved precision measurements of helium $2^3P$ fine structure

Thermal helium $2^3S$ metastable atoms can be detected with near unit efficiency by the electron ejected when they strike a stainless-steel surface. However, the $2^1S$ atoms and UV photons created in generating the metastable beam also produce ejected electrons. We remove the $2^1S$ atoms from our beam using 2.06-micron photons from a dc discharge lamp to drive the $2^1S$ atoms to the $2^1P$ state (which subsequently decays to the ground state). A Stern-Gerlach magnet removes the m=-1 and m=+1 $2^3S$ atoms. Elastic collisions with argon gas scatters the $2^3S$ atoms out of the initial beam path, and thus away from the direction of the UV photons. The combination of these elements allows for high-efficiency detection of $2^3S_1$ m=0 atoms with very low background due to singlet atoms, UV photons or $2^3S_1$ m=$\pm$1 atoms, allowing for an improved signal-to-noise ratio for precision helium fine-structure measurements.   

Nuclear spin-dependent parity violation in Cs and Fr

The study of parity nonconservation (PNC) in cesium led to a first measurement of the nuclear anapole moment and allowed to place constraints on weak meson-nucleon couplings. These constraints were found to be in disagreement with the ones obtained from nuclear parity violating experiments. The discrepancy of the nuclear and atomic PNC studies motivated further investigation of Cs spin-depended PNC amplitude. The Fr experimental work is in progress at TRIUMF [Sheng et al., J. Phys. B 43, 074004 (2010)] and theoretical calculations are needed for future interpretation of the results. In this work, we carried out high-precision relativistic all-order calculations of the spin-dependent PNC amplitudes in the $6s-7s$ transition in Cs and the $7s-8s$ transition in Fr using relativistic all-order methods in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. The new Cs all-order result was found to be consistent with the older atomic physics value of the anapole coupling constant. The nuclear spin-dependent PNC amplitudes between the hyperfine structure components of the ground state of Fr are also evaluated. The dependence of the results on the values of nuclear parameters is investigated.   

High Resolution Rotational Spectroscopy of Zeeman {\&} Hyperfine Effects in PbF {\&} YbF

Motivated by the ongoing search for the CP-violating electron electric dipole moment (e-EDM), rotational spectra of the radicals$^{ 207}$Pb$^{19}$F and $^{208}$Pb$^{19}$F were measured using a supersonic jet Fourier transform microwave spectrometer. Zeeman splitting was examined for 10 $^{207}$PbF and 9 $^{208}$PbF J = $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $ and J = $^{3}$/$_{2}$ transitions using Helmholtz coils and magnetic fields up to $\sim $4 Gauss. Transitions were observed with 0.5 kHz accuracy and 6 kHz pair resolution over a range of 2 -- 26.5 GHz. The observation of these field dependent spectra allowed for the determination of the two body fixed g-factors, G$_{\parallel}$ and G$_{\perp}$, of the electronic wave function. This is an important step in a possible future e-EDM experiment using either the $^{207}$PbF or $^{208}$PbF molecule, and our results compare reasonably well with recently calculated values. Observing the nuclear quadrupole hyperfine structure can also help characterize the critical electric field at the heavy atom nucleus in unstable but long-lived $^{205}$PbF as well as $^{173}$YbF. Energy level predictions based on our detailed studies of the 4 stable PbF isotopologues as well as previous optical and microwave spectra of YbF will facilitate upcoming experimental studies and may also uncover nearby states of opposite parity which could also greatly benefit the eEDM search.   

Optical lattice clock: towards $10^{-17}$ uncertainty

Ultracold alkaine-earth atoms confined in an optical lattice are strong candidates for high-accuracy frequency standards and precision timekeepers. When last evaluated, the ytterbium optical lattice clock fractional uncertainty was $3.4\times10^{-16}$. Principle contributions to this uncertainty were the blackbody Stark effect, atomic cold-collisions, and lattice ac-Stark shifts not canceled at the magic wavelength balancing scalar Stark shifts in clock states $^1\!S_0$ and $^3\!P_0$. We report significant advances in these areas, paving the way toward a total uncertainty near the $10^{-17}$ level. We have since measured the clock static polarizability, reducing the blackbody Stark shift uncertainty to $3\times10^{-17}$, now limited by thermal environment uncertainty. Ultracold collisions between fermionic $^{171}$Yb atoms are dominated by p-wave interactions between $^1\!S_0$ and $^3\!P_0$ states. Ramsey spectroscopy with $\approx$~50\% excitation cancels density-dependent shifts at the $5\times10^{-18}$ level. We report progress measuring residual lattice ac-Stark shifts: polarizability away from the magic wavelength ($\propto I$, the lattice intensity), hyperpolarizability ($\propto I^2$) and multipole (M1-E2) effects ($\propto\sqrt{I}$).   

Investigation of the optical transition of the $^{229}$Th nucleus in a solid-state environment

We describe a novel approach to directly measure the energy of the narrow, low-lying isomeric state in $^{229}$Th. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we argue that the $^{229}$Th optical nuclear transition may be driven inside a host crystal with a high transition Q. This technique might also allow for the construction of a solid-state optical frequency reference that surpasses the precision of current optical clocks, as well as improved limits on the variability of fundamental constants. Based on analysis of the crystal lattice environment, we argue that a precision of $ 3 * 10^{ - 17 } < \Delta f/f < 1 * 10^{ - 15 }$ after 1~s of photon collection may be achieved with a systematic-limited accuracy of $\Delta$f/f $\sim$ 2 * 10$^{ - 16 }$. Improvement by a factor of 10$^2$ to 10$^3$ of the constraints on the variability of several important fundamental constants also appears possible. We report on recent results aimed at directly measuring fluorescence from the transition.   

A Cavity Enhanced $^{87}Sr$ Optical Lattice Clock

Optical lattice clocks based on alkaline earth atoms have the potential to outperform single atomic ion clocks (the best clocks to date) [1,2]. The promise of lattice clocks is due to their larger atom numbers, for quantum projection noise limited atomic clocks average down like $1 / \sqrt{N_{atoms}}$. Our new $^{87}Sr$ optical lattice clock utilizes a cavity enhanced 1D magic wavelength lattice to further improve our atom number [3]. The circulating power in our cavity allows us to operate at larger trap volumes than our previous retroreflected configuration while maintaining reasonable trap depths. These larger trap volumes enable us to transfer many more atoms into our lattice, improving our signal to noise. We will discuss our new cavity lattice clock system, and progress toward a comparison of two JILA lattice clocks will also be discussed. We will also touch on our goal of a 3D cavity enhanced lattice clock geometry. \\[4pt] [1] A.D. Ludlow et al, Science 319, 1805 (2008)\\[0pt] [2] T. Rosenband et al, Science 319, 1808 (2008)\\[0pt] [3] P.G. Westergaard et al, PRL 106, 210801 (2011)   

Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35{\%}. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5{\%}. \\[4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).\\[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).\\[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).   

Interaction of Wave Packets with an Oscillating Gaussian Barrier

We use classical, semiclassical, and quantum mechanics to examine a propagating wave packet that encounters an oscillating Gaussian potential barrier. The wave packet can be transmitted, reflected, or partially reflected and partially transmitted. The final wavefunction is constructed both semiclassically and quantum mechanically, and we examine the agreement between these two methods. It is believed that multiple oscillating Gaussian potential barriers may serve as a quantum pumping mechanism for ultracold atoms [1]. We have chosen to study first a simpler case, that of a single oscillating Gaussian barrier, with the intention of using these results for studying cases with multiple barriers.   

Proposal for unfolding single biomolecules in an ion trap

The functionality of biological molecules such as nucleic acids, proteins, and carbohydrates are driven by both their chemical composition and conformation. Ion trap mass spectrometry of large biomolecules is a well-established technique for primary sequence determination (composition) and is finding increasing use in investigating higher-order structure (conformation). Confining single isolated biomolecules in a ion trap provides a uniquely adaptable environment in which to investigate higher-order structure through manipulation of the surrounding solvent cage, temperature, and net charge at the single quantum level. We propose continuously observing these conformational changes in-trap though optical fluorescence techniques developed for in-vitro and in-vivo studies including F\"{o}rster Resonance Energy Transfer (FRET) and super-resolution microscopy.   

A miniature mechanical shutter for atomic beams

In many atomic physics experiments, atomic beams are generated for transport of atoms from a region of high (HV) to ultra-high vacuum (UHV). In such experiments, as well as those requiring a large number of atoms, it is desirable to load an atomic trap by a high flux source, such as a pyramidal magneto-optic trap (MOT) or Zeeman slower, without having the trap be affected by the atomic beam once loading is completed and subsequent experimental steps are initiated. We present here a mechanical shutter intended for this purpose in a BEC experiment. By implementing the shutter, we hope to block not only the beam, but other gases from entering the main chamber, resulting in improved evaporative cooling efficiency, which in turn will allow us to form BECs more quickly and easily. The shutter design discussed in detail here is unique in its small size (less than 5 mm in diameter, encompassing a magnet, steel rod, solenoid, and mu metal for magnetic shielding) and UHV compatibility. Performance parameters of the shuttering mechanism are also presented.   

Silica Nanowire Growth on Photonic Crystal Fiber by Pulsed Femtosecond Laser Deposition

We present a new method of nanowire fabrication using pulsed laser deposition. An 800 mW 1 GHz femtosecond Ti:Sapphire laser is guided into a polarization-maintaining photonic crystal fiber (PCF). The PCF, with a core tapered to 1.7 micron diameter, converts femtosecond laser pulses centered at 800 nm into green light with a spectrum down to 500 nm. The PCF is enclosed in a cylindrical tube with glass windows, sealed in a class 100 clean room with silicone-based RTV adhesive. The high power of each laser pulse in a silica-rich environment leads to growth of a silica nanowire at the output end of the PCF. SEM analysis shows that the nanowire is 720 nm in diameter and grows at a rate of about 0.6 um/s. Details of nanowire performance along with potential applications will be presented.   

Optical heterodyne analysis of picosecond laser pulses

We present an optical heterodyne method to analyze laser pulses of picosecond duration using a frequency stabilized nanosecond laser. Optical heterodyning requires the linewidth of the nanosecond laser to be much smaller than the linewidth of the picosecond pulse being analyzed. This condition is easily achieved for seeded single-longitudinal-mode nanosecond lasers and seeded nanosecond OPOs. The timing of the two collinear lasers is adjusted such that the picosecond laser pulse arrives near the center of the nanosecond pulse, which fills the role normally performed by a CW laser. The beat pattern between the laser pulses is measured on a streak camera and analyzed through Fourier analysis.   

Sommerfeld's Geometric View of Relativistic Vector Spaces: A Neglected Insight Revived

In 1909 Sommerfeld showed that the structure of a space-time 4-vector $\left( {\Delta {\rm {\bf r}},ic\Delta t} \right)$ implies that relativistic velocity vectors \textbf{v} occupy the space of geodesics on the 3-surface of a hypersphere of imaginary radius $S_{\mbox{vel}} =ic$. This peculiar-seeming result in relativistic 4-space is comparable to the existence of a real sphere within a Euclidean 3-space, and Sommerfeld recognized it later (1931) as implying a spherical 3-space of negative-curvature Lobachevsky geometry within the flat relativistic 4-space. These deductions are mathematically rigorous, and the implications for velocity vectors were accepted and used by Einstein (1921), but they have generally been ignored. The insights offered by Sommerfeld's geometric view are complementary to what the prevailing tensor techniques can do. I show how they can be readily extended and applied, developing new insights and results, including (a) a hyperbolic polar representation of velocity 4-vectors, (b) the equivalent representation for position-time 4-vectors, (c) a connection like that of a sphere with a tangent plane, joining relativistic 4-vectors and their nonrelativistic equivalents, providing quantitative connection formulas.   

Atomic Au and Pd Negative-Ion Catalysis of H$_{2}$O, HDO, and D$_{2}$O to Corresponding Peroxides

Fundamental ideas of muon-catalyzed fusion utilizing a negative muon, a deuteron and/or a triton, have been used in atomic Au and Pd negative ion-catalysis of H$_{2}$O$_{2}$, HDO$_{2}$, and D$_{2}$O$_{2}$ from H$_{2}$O, HDO, and D$_{2}$O, respectively, finding that Au$^{-}$ is an excellent catalyst but the Pd$^{-}$ ion has a higher catalytic effect, consistent with recent observations. The fundamental atomic mechanism responsible for the oxidation of water to peroxide has been attributed to the interplay between Regge resonances and Ramsauer-Townsend minima in low energy electron elastic total cross sections for Au and Pd atoms, along with their large electron affinities. Dispersion-corrected density-functional theory transition state calculations performed on atomic Au$^{-}$ catalysis of water conversion to H$_{2}$O$_{2}$, have revealed that the formation of the Au$^{-}$(H$_{2}$O)$_{2}$ anion molecular complex in the transition state, provides the fundamental mechanism for breaking the hydrogen bonding strength in the catalysis of H$_{2}$O$_{2}$ using the Au$^{-}$ ion. Thus, the crucial link between low-energy electron elastic scattering resonances and low-energy chemical reaction dynamics has now been fully established.   

Towards Probing Living Cell Function with NV Centers in Nanodiamonds

We report on recent progress in using nitrogen-vacancy (NV) centers in nanodiamonds as local probes of radical concentrations in living cells. Nanodiamonds are biologically inert, and NV centers within them are robust and can sense local magnetic fields with nanoscale resolution. The ability to monitor the local magnetic environment within the cell would provide a new tool to study organelle function during normal operation or in response to applied stimuli. In addition, radical concentrations have been linked to cancer, aging, and signaling between cells, thus proving to be of significant importance to the biological and medical sciences.   

Applications of Nuclear Spin Singlet States in Liquids and Solids

We explore applications of singlet states created from pairs of nuclear spins both in solutions and in solids. The singlet state is resistant to many decoherence mechanisms and can exhibit long coherence times. We show that measuring the decoherence of the singlet state allows us to detect intermolecular interactions, such as those due to binding between molecules. We also demonstrate that by manipulating the singlet states on target molecules we can extract spectral lines of the target that are overlapped by interfering peaks. Finally, we discuss the possibility of using singlet states in quantum-memory schemes in the solid-state.   

Depletion-based techniques for super-resolution imaging of NV-diamond

We discuss the development and application of depletion-based techniques for super-resolution imaging of NV centers in diamond: stimulated emission depletion (STED), metastable ground state depletion (GSD), and dark state depletion (DSD). NV centers in diamond do not bleach under optical excitation, are not biotoxic, and have long-lived electronic spin coherence and spin-state-dependent fluorescence. Thus NV-diamond has great potential as a fluorescent biomarker and as a magnetic biosensor.   

Altered States of Solid Xenon

Relaxation processes and structure in solid Xe were studied using hyperpolarization of $^{129}$Xe via spin-exchange from optically pumped Rb. In an applied field of 2T, we studied both longitudinal and transverse $^{129}$Xe relaxation; the former as a function of freezing conditions and the latter as a function of both freezing conditions and dilution of $^{129}$Xe and $^{131}$Xe atoms relative to spin-zero species. A flow-through polarizer [1] is used to freeze and collect solid Xe (both $^{129}$Xe-enriched and naturally abundant), where we adjust the partial pressure of Xe in order to alter freezing conditions, which yield reproducible differences in spin-lattice relaxation times of greater than 10{\%}, apparently by varying the grain size. This is surprising because the mechanism is supposed to be a bulk Raman-phonon scattering process. In a separate convection cell [2] experiment, we find that reducing the concentration of $^{129}$Xe and $^{131}$Xe narrows the NMR line shape, as expected. However, several anomalous features also arise, depending on the freezing rate. Dilute concentrations of spin-1/2 $^{129}$Xe range from 10{\%} to below 1{\%}.\\[4pt] [1] Schrank, et al., PRA 80, 063424 (2009).\\[0pt] [2] Su, et al., APL 85, 2429 (2004).   

Impact of Decoherence on Internal State Cooling using Optical Frequency Combs

We discuss femtosecond Raman type techniques to control molecular vibrations, which can be implemented for internal state cooling from Feshbach states with the use of optical frequency combs. We analyzed the use of an optical frequency comb, with and without modulation, as a viable substitute to the STIRAP process. In our theoretical model we take into account decoherence in the form of spontaneous emission and collisional dephasing in order to ascertain an accurate model of the population transfer in a three level system. We analyze the effects of odd and even chirps of the optical frequency comb in the form of sine and cosine functions on the population transfer. We compared the effects of these chirps to the results attained with a standard optical frequency comb to see if they increase the number of molecules that eventually end up in the final deeply bound state in the presence of decoherence. We also analyzed the inherent phase relation of the collisional dephasing between each of the states. This ability to control the rovibrational states of a molecule with an optical frequency comb enables us to create a deeply bound ultracold polar molecule from the Feshbach state.   

Quantum and classical analysis of circular and sectorial billiards with central harmonic potential

We present the classical and quantum solutions to a particle confined in a circular sectorial billiard under a central harmonic potential, attractive and repulsive. The classical analysis is done by applying the Hamilton-Jacobi formalism; we derive the characteristic equations for periodic orbits, give expressions for the length of the trajectories in terms of elliptic integrals and study some geometrical constructions for the billiard. The quantum analysis leads to the study of the confluent hypergeometric function, from which we obtain the characteristic values for the energy spectra and the probability distributions inside the circular and sectorial billiard. As verification for the attractive case, as we increase the billiard radius our results approach the unbounded solutions. Finally we compare the classical probability distributions, obtained by assuming the probability as proportional to the time spent by the particle in each space interval, with the quantum ones.   

Quadratically coupled optomechanical systems

Typical optomechanical systems are composed of high finesse optical cavities that are coupled to mechanical oscillators, which are promising for classical as well as quantum applications. A well studied optomechanical configuration involves a optical cavity that is linearly coupled to the displacement of the mechanical oscillator. However, a quadratic coupling can also be realized between the cavity and the displacement of the mechanical oscillator using membranes, cold atoms, or microdisk-resonators. In the poster, I will describe our analysis of this new kind of coupling. The results include the exact solution of the corresponding Hamiltonian (in the absence of dissipation), a discussion of the spectrum and the eigenstates, and of the dynamics of the unitary evolution of the system. I will also discuss work planned for the future.   

Optical Production and Control of Photonic Structures

Coherent control of the refractive index with vanishing absorption in multilevel systems and its applications were a subject of intense recent experimental and theoretical research [1-3]. We study the new possibility to use the coherent control of refractive index for optical production and control of photonic structures, such as distributed Bragg reflectors (DBR), holey fibers, photonic band gaps, and photonic crystals. We consider the construction of photonic structures in resonant homogeneous atomic media through the illumination laser field standing waves. Using sharp variation of refractive index, we can make the detuning from resonance spatially dependent and eliminate a resonant absorption on this detuning. This can be realized in three-level atoms in nearly degenerate ladder configuration with a populated intermediate level which position in space is modulated by an external control standing wave of a laser field via ac-Stark effect. We analyze the optimal geometry for realization of the proposed method and its possible implementation in rare-earth doped crystals with excited state absorption.\\[4pt] [1] N. Priote, et al., PRL 101, 147401 (2008).\newline [2] C.O'Brien and O.Kocharovskaya, Phys. Rev. Lett., 107, 137401 (2011).\newline [3] A. Kalachev and O. Kocharovskaya, Phys. Rev. A 83, 053849 (2011).   

Investigation of alkali-wall interactions in antirelaxation-coated vapor cells

In experiments which employ room-temperature alkali vapors, antirelaxation coatings can dramatically increase the relaxation times of alkali atoms within a vapor cell. These coatings are crucial in many atomic physics experiments, such as: atomic magnetometry, electromagnetically induced transparency, atomic clocks, quantum control and measurement, etc. It is observed that the coatings have strong initial interactions with the alkali vapor after they are prepared, including suppression of alkali-vapor density and modification of the spin relaxation times. Cell curing refers to the change in properties of the internal surfaces of the vapor cells. We aim to understand what is going on during the initial interaction in order to possibly improve the coatings. In this experiment, to investigate how the interaction changes with time, we measure the rubidium vapor density using D1 line while tracking the rubidium vapor diffusing in a long coated glass tube. Further investigations include the relation between light induced atomic desorption and cell curing.   

Collective state measurement of mesoscopic ensembles with single-atom resolution

For mesoscopic ensembles containing 100 or more atoms we measure the total atom number and the number of atoms in a specific hyperfine state with single-atom resolution. The measurement detects an atom-induced frequency shift of an optical cavity containing the ensemble. This work extends the range of cavity-based detection with single-atom resolution by more than an order of magnitude in atom number, and provides the readout capability necessary for Heisenberg-limited atom interferometry.   

Experimental Angular Resolved Luminescence Measurements of Eu Ions in MgF$_{2}$

The angular emission from Eu$^{2+}$ ions in a system Al(substrat)/ MgF$_{2}$:Eu$^{2+}$/Al is measured. The thickness of the MgF$_{2}$:Eu$^{2+}$ films were optimized to support two guided mode, one at 323 nm and other at 420nm, whose values correspond to the excitation and emission wavelength of the Eu$^{2+}$ ions, respectively. The coupling of the incident light to the guided mode was obtained by appropriate selection of the thickness of the Al film. When the guided mode in the excitation wavelength is excited, more Eu$^{2+}$ elements in the waveguide are excited and therefore more elements contribute to the emission. If also, a guided mode in the emission wavelength is excited, it produces in the emission band of Eu$^{2+}$ an increment of it value. Therefore, the spatial distribution of emission light as a function of the angle of incidence is enhanced in resonant condition as compared with off-resonance condition due to the incident light travels along the guide more efficiently.   

Electron Microscopy of Quantum Gases

The technique of scanning electron microscopy allows for the investigation of solid surfaces and structures with a spatial resolution of few nanometers. Extending the application of this tool to a cloud of ultracold atoms, we obtain a novel way to image and manipulate the gaseous target, characterized by high spatial and temporal resolutions and by single atom sensitivity. A focussed electron beam is moved over the cloud and ionizes the atoms by electron impact ionization. The produced ions are subsequently extracted and detected. We successfully employed the technique for in situ imaging of ultracold atomic clouds, for single site addressability in optical lattices and for the observation of temporal correlations in a cold samples, both in 3d and 1d. The electron beam can also be used to locally introduce losses, thus paving the way to investigate dissipative processes in quantum gases and to generate topological defects.   

Electron Dynamics with a Mixed Moving/Fixed Frozen Gaussian Basis Set

In this report we simulate the strong field ionization of He atom using frozen Gaussian functions and demonstrate the importance of accurate bound state wavefunction in such a calculation. We expand the time-dependent electronic wavefunction using both static atom-centered Gaussian basis functions and trajectory-guided Gaussian wavepackets. We show that the ground state can be accurately described with a small basis set and we further show that this leads to an improved description of time-dependent processes such as ionization in strong fields. Our method combines the advantages of moving Gaussian wavepackets in the context of strong field attosecond phenomena with the advantages of traditional quantum chemistry techniques for describing low lying electronic states. We have computed the single ionization yield of He atom following its interaction with a 12 fs, 805 nm pulse, and show that the combination of static and moving basis set gives a highly correlated picture of the ionization event. We also computed the potential energy curves of H$_2$ to show that our method describes the nuclear-dependence of electronic structure very well. In this work, the nuclei are fixed. However, we show how it is possible to model electronic and nuclear dynamics on the same footing.   

Observation of local temporal correlations in trapped quantum gases

We measure the temporal pair correlation function of a 3-dimensional trapped gas of bosons above and below the critical temperature for Bose-Einstein condensation. The measurement is performed in situ using a local, time-resolved single-atom sensitive probing technique, based on scanning electron microscopy. Third and fourth order correlation functions are also extracted from the same data. We futher extend this diagnostics to samples of few 1-dimensional tubes of ultracold bosons in the quasi-condensate and strongly interacting regimes, obtaining, in the second case, clear antibunching signal as a consequence of interaction induced ``fermionization.'' Our results promote temporal correlations as new observables to study the dynamical evolution of ultracold quantum gases.   

Hyperfine frequency shift and Zeeman relaxation in alkali vapor cells with anti-relaxation alkene coating

A recently identified alkene based anti-relaxation coating exhibit Zeeman relaxation times in excess of 60~s in alkali vapor cells (two orders of magnitude longer than in paraffin coated cells). The long relaxation times, motivate revisiting the long-standing question of what is the mechanism underlying wall-collision induced relaxation and renew interest in applications of alkali vapor cells to secondary frequency standards. We measure the Zeeman relaxation time, and the width and frequency shift of the clock resonance, in $^{85}$Rb and $^{87}$Rb vapor cells with alkene anti-relaxation coating. We compare the results with those in paraffin coated cells. We find that the frequency shift is slightly larger than for paraffin coated cells. However we observe that the Zeeman relaxation rate appears to be a linear function of the hyperfine frequency shift, whereas a linear dependence was not observed in paraffin coated cells. To shed light on this result we propose a model describing different Zeeman relaxation mechanisms of alkene and alkane cell-wall coatings.   

Methods to Characterize Vapor Cell Performance for Nuclear Magnetic Resonance Applications

The Advanced Sensors Development team at Northrop Grumman, Navigation Systems Division is developing a Nuclear Magnetic Resonance Gyroscope (NMRG). Various methods to measure atomic spin lifetimes in vapor cells for predicting NMRG performance have been investigated. Certain methods show clear advantages over others by reducing required testing times and improving test data resolution. New modifications of methods were also developed to study and improve the precision and repeatability of test results. These methods help correlate vapor cell performance to cell filling and sealing methods for cell fabrication process improvement. The vapor cells produced in conjunction with these techniques have exhibited significant and consistent increases in both the noble gas spin lifetimes and the NMR signal strengths compared to previous cell fabrication processes, providing more precise insight into cell development techniques.   

Nuclear Magnetic Resonance Gyroscope

The navigation grade micro Nuclear Magnetic Resonance Gyroscope (micro-NMRG) being developed by the Northrop Grumman Corporation is concluding the fourth and final phase of the DARPA Navigation Grade Integrated Micro Gyro (NGIMG) program. Traditional MEMS gyros utilize springs as an inherent part of the sensing mechanism, leading to bias and scale factor sensitivity to acceleration and vibration. As a result, they have not met performance expectations in real world environments and to date have been limited to tactical grade applications. The Nuclear Magnetic Resonance Gyroscope (NMRG) utilizes the fixed precession rate of a nuclear spin in a constant magnetic field as an inertial reference for determining rotation. The nuclear spin precession rate sensitivity to acceleration and vibration is negligible for most applications. Therefore, the application of new micro and batch fabrication methods to NMRG technology holds great promise for navigation grade performance in a low cost and compact gyro. This poster will describe the history, operational principles, and design basics of the NMRG including an overview of the NSD designs developed and demonstrated in the DARPA gyro development program. General performance results from phases 3 and 4 will also be presented.   

Electron Paramagnetic Resonance -- Nuclear Magnetic Resonance Three Axis Vector Magnetometer

The Northrop Grumman Corporation is leveraging the technology developed for the Nuclear Magnetic Resonance Gyroscope (NMRG) to build a combined Electron Paramagnetic Resonance -- Nuclear Magnetic Resonance (EPR-NMR) magnetometer. The EPR-NMR approach provides a high bandwidth and high sensitivity simultaneous measurement of all three vector components of the magnetic field averaged over the small volume of the sensor's one vapor cell. This poster will describe the history, operational principles, and design basics of the EPR-NMR magnetometer including an overview of the NSD designs developed and demonstrated to date. General performance results will also be presented.   

Alignment Effects in the Fully Quantum State Resolved Inelastic NO(X) + Rare Gas Collisions

The rotational alignment effects in the rotationally inelastic scattering of NO(X$^{2}\Pi _{1/2})$ with Ar and Kr have been investigated by means of quantum mechanical, quasi-classical trajectory, and Monte Carlo scattering calculations. It has been shown that the repulsive nature of the interaction potential at a collision energy of 65meV is primarily responsible for the rotational alignment. On the other hand, the alternating trend in the integrated quantum mechanical parity resolved alignment moments as a function of the final rotational state reflects differences in the differential cross sections for the total NO(X) parity conserving and changing collisions due to quantum interferences, rather than a difference in stereodynamics. Ion-images for NO(X) resolved in \textit{$\Lambda $}-doublet levels were collected with a hexapole state selective cross molecular beam ion-imaging apparatus using linearly polarised light. Scattering angle resolved rotational alignment moments were retrieved from the images using a newly developed data analysis algorithm. The agreement is excellent between the experimental and the quantum data. To the best of our knowledge this is the first instance when experimental \textit{$\Lambda $}-doublet resolved alignment moments are reported.   

Femtosecond time-resolved imaging of torsion in an axially chiral molecule

The use of laser pulses to control the transition from one enantiomer of a chiral molecule to its mirror form has been the subject of a large number of \textit{theoretical} studies driven by the intriguing prospects of light-induced deracemization, i.e. creation of enantiomeric excess. Here we provide new \textit{experimental} insights to how the combination of long (nanosecond) and short (femtosecond) laser pulses can be used to induce torsion in an axially chiral biphenyl derivative, here 3,5-diuoro-3',5'-dibromo-4'-cyanobiphenyl. The long, elliptically polarized, laser pulse 3D aligns the molecule, and the, linearly polarized, short pulse initiates torsion about the stereogenic axis. The torsional motion is monitored directly by determining the dihedral angle using femtosecond time-resolved Coulomb explosion imaging. At short times (0-4 ps) torsion occurs with a period of 1.25 picoseconds and an amplitude of 3\r{ } in excellent agreement with theoretical calculations. At longer times torsion is blurred by delocalization of the molecular orientation due to overall rotation of the molecule consistent with our theoretical model. Furthermore, a new imaging analysis technique, relying on the correlation between the ejected ionic fragments, supports our interpretation of the experimental data.   

Orientation-dependent ionization yields from strong-field ionization of fixed-in-space linear and asymmetric top molecules

The ionization step leading to single ionization in the multiphoton or tunnel ionization regime is a fundamental process which is thought to be well understood for atoms; however, for larger molecules much less is known. Of particular importance is the understanding of the dependence of the initial ionization step on the molecular orientation with respect to the external field. To fully test existing theories and to guide the way for new theory development, we here extend these experiments to larger and more complex molecular systems: Carbonyl sulphide (OCS), benzonitrile and naphthalene. In particular we investigate the yield of strong-field ionization, by a linearly polarized probe pulse, as a function of the relative orientation between the laser field and the molecule. This is achieved using standard laser alignment techniques to produce 1D or 3D aligned molecular ensembles before a femtosecond laser probe pulse singly ionizes the target molecules. For naphthalene and benzonitrile, the orientational dependence of the ionization yield agrees well with the calculated results, in particular, we observe that ionization is maximized when the probe laser is polarized along the most polarizable axis. For OCS the observation of the maximum ionization yield when the probe is perpendicular to the internuclear axis contrasts the theoretical results.   

Monte Carlo Ground State Energy for Trapped Boson Systems

Diffusion Monte Carlo (DMC) and Green's Function Monte Carlo (GFMC) algorithms were implemented to obtain numerical approximations for the ground state energies of systems of bosons in a harmonic trap potential. Gaussian pairwise particle interactions of the form $V_0 e^{-{|r_i-r_j|^2}/{{r_0}^2}}$ were implemented in the DMC code. These results were verified for small values of $V_0$ via a first-order perturbation theory approximation for which the N-particle matrix element evaluated to ${N\choose2} \frac{V_0}{(1 + 1/{r_0}^2)^{3/2}}$. By obtaining the scattering length from the 2-body potential in the perturbative regime ($\frac{V_0}{\hbar\omega} \ll 1$), ground state energy results were compared to modern renormalized models by P.R. Johnson \emph{et. al}, New J. Phys. {\bf 11}, 093022 (2009).   

Seconds-scale Light Storage

We report on achieving ultra-long lifetimes for coherent light storage. An optically thick sample of 87Rb confined in a far-off-resonance optical lattice is used as the storage medium. Ground state differential Stark shift is compensated via ``magic'' magnetic field technique. The observed 1/e lifetime for storage and retrieval protocol employing the clock (0-0) transition is 5 s. After the storage protocol is augmented by a dynamic decoupling with a sequence of microwave pi-pulses, the 1/e lifetime for storage of coherent light is further increased, up to 16 s.   

Investigation of Transparent Silicon Carbide Proprieties for Atom Chips Sensors

Atom chips are an efficient tool for trapping, cooling and manipulating cold atoms. This is in particular due to the fact that they can achieve strong magnetic field gradients near the chip surface, hence strong atomic confinement. However, this advantage typically comes at the price of reducing the optical access to the atoms, which are confined very close to the chip surface. Moreover, the maximum achievable confinement strongly depends on thermal management issues within the atom chip. We report in the following experimental investigations showing how these limits could be pushed further by using an atom chip made of a gold microcircuit deposited on a single-crystal Silicon Carbide (SiC) substrate. With a band gap energy value of about 3.2 eV at room temperature, the latter material is transparent at 780nm, potentially restoring quasi full optical access to the atoms. Moreover, it combines a very high electrical resistivity (over 105 W.cm ) with a very high thermal conductivity (over 390~W.m-1.K-1), making it a good candidate for supporting wires with large currents without the need of any additional electrical insulation layer. We have demonstrated robust magneto-optical trapping (MOT) of about one million rubidium atoms through the SiC chip.   

Generation of Tunable, Coherent Terahertz Radiation Through Molecular Modulation

We introduce and numerically model an approach for generating coherent terahertz radiation. Our method is based on our experimental work with high frequency (10-100 THz) continuous-wave light modulation. We use continuous-wave stimulated Raman scattering inside a high-finesse cavity to modulate light at molecular frequencies. Our simulations demonstrate how this approach could be expanded to generate radiation outside of the optical range. An infrared mixing beam from a semiconductor diode laser could be frequency down-shifted by the molecular modulator in order to generate radiation in the terahertz region of the spectrum. The generated radiation would be easily tunable, as a tuning range of a few tens of nanometers in the diode laser would allow for generation of radiation spanning the entire terahertz region (1-10 THz). We explore the efficiency of this generation using numerical simulations with experimentally available parameters.