Bulletin of the American Physical Society
45th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 59, Number 8
Monday–Friday, June 2–6, 2014; Madison, Wisconsin
Session Q1: Poster Session III (2:00pm - 4:00pm) |
Hide Abstracts |
Room: Exhibit Hall |
|
Q1.00001: COLD ATOMS, MOLECULES AND PLASMAS |
|
Q1.00002: Early Time, Fast Collisional Dynamics of Equilibriating Ions in a Strongly Coupled Ultracold Neutral Plasma Trevor Strickler, Patrick McQuillen, Thomas Langin, Thomas Killian, Georg Bannasch, Thomas Pohl Collision rates in weakly-coupled plasmas are well-described by the Landau-Spitzer formula. In the regime of strong coupling, however, the formula breaks down. This has motivated much theoretical and experimental work to study collision rates in strongly-coupled plasmas. In previous work, we have demonstrated direct measurements of thermalization rates in strongly-coupled ultracold neutral plasmas (UCNPs) created by photoionizing strontium atoms in magneto-optical trap. Our technique used optical pumping to create spin ``tagged'' subpopulations of ions having skewed velocity distributions. With LIF imaging, we measured the equilibration of the skewed velocity profiles to extract ion collision rates. We are now using these techniques to explore the early time dynamics of these skewed ion velocity distributions in the first 100ns after optical pumping. Molecular dynamics simulations of strongly coupled plasmas predict deviations from the exponential decay of average skewed velocity that is expected for weakly coupled plasmas. We use probe laser pulses on the order of 30ns to measure the relaxation of the skewed velocity profiles to test the theoretical predictions. [Preview Abstract] |
|
Q1.00003: Simulations of Flourescence Imaging of an Ultracold Neutral Plasma Including Dark State Pumping Thomas Langin, Patrick McQuillen, Trevor Strickler, Thomas Killian Ultracold neutral plasmas of strontium are generated by photoionizing laser-cooled atoms. The plasma evolution is probed by imaging light scattered via the 5s$^{2}$S$_{1/2}$-5p$^{2}$P$_{1/2}$ ion transition. Spectra are obtained by taking a series of images at varying laser detunings. The ion temperature, $T$, is then measured by fitting a Voigt profile to obtain the Doppler width. However, 5p$^{2}$P$_{1/2}$ ions have a 7\% chance of decaying to the metastable 5d $^{2}$D$_{3/2}$ state. Thus, close to resonance, where it's more likely for an ion to scatter multiple photons during the imaging process, the observed signal will be depressed due to optical pumping to the dark $^{2}$D$_{3/2}$ state. This causes an artificial broadening in the spectra and thus artificially high $T$ measurements. We have developed a method for simulating the imaging process in order to determine the imaging durations, $t$, and light intensities, $I$, for which this effect becomes significant. This is both to determine the regime for which Voigt profile fitting yields an accurate $T$ measurement and to develop a new spectra fitting tool which provides accurate $T$ measurements in the high $I$ and $t$ (and thus high signal) regimes. [Preview Abstract] |
|
Q1.00004: Magneto-optical trapping of a diatomic molecule Daniel McCarron, John Barry, Eric Norrgard, Matthew Steinecker, David DeMille Laser cooling and trapping are central within modern atomic physics. The common workhorse within this field is the magneto-optical trap (MOT) which combines the power of laser cooling with a restoring force from radiation pressure. This robust technique can produce large samples of a variety of atomic species at ultracold temperatures; providing an ideal starting point for the study of a wide range of phenomena from optical clocks to quantum degeneracy. A MOT for molecules would provide a similarly powerful starting point for the study and manipulation of ultracold molecules. Possible applications range from quantum information and simulation to precision measurements to access to the world of ultracold chemistry. We will present data demonstrating the three-dimensional magneto-optical trapping of a diatomic molecule. Our experiment uses a bright and slow cryogenic molecular beam of strontium monofluoride (SrF). Molecules in the beam are laser-slowed via radiation pressure to enable loading of the MOT. MOT properties are diagnosed from images of laser induced fluorescence in the trapping region. Details of our molecular MOT will be presented including number, temperature and density. [Preview Abstract] |
|
Q1.00005: Damping of excitations in a dipolar Bose gas Ryan Wilson, Stefan Natu In a Bose-condensed gas, quasiparticle excitations can undergo damping via effective condensate-mediated interactions in the collisionless regime. Motivated by recent experimental advances with condensates of highly magnetic atoms, we consider quasiparticle damping in Bose gases with dipolar interactions, where the dispersion exhibits a roton-maxon character in the appropriate trapping geometry. Following standard perturbative arguments, we derive the rates for quasiparticle damping in a collisionless Bose gas interacting with long-range interactions. We find that in the experimentally relevant temperature regime, phonons and rotons are effectively undamped in a dipolar gas owing to the nature of the low energy dispersion. Furthermore, by tuning the external magnetic field, the dipolar interaction can be made strongly anisotropic, which leads to a non-trivial dependence of the damping processes on the direction of the applied magnetic field. We discuss the implications of this work for recent experiments with highly magnetic atoms. [Preview Abstract] |
|
Q1.00006: Vortex nucleation in a Bose-Einstein condensate circulating in an anharmonic trapping potential Seji Kang, Jae-yoon Choi, Sang Won Seo, Yong-il Shin When a Bose-Einstein condensate moves in an anharmonic trapping potential, the center-of-mass motion of the condensate can affect its internal superfluid dynamics in contrast to the case of a harmonic potential. We study condensate dynamics in an externally driven anharmonic potential and observe that vortices are nucleated when the condensate circulates in the anharmonic trap. In our experiment, the anharmonic trapping potential is provided by a magnetic quadrupole field and an external driving force is applied with modulating external bias fields. Under a resonant circular drive, the trapped condensate shape rotates in phase with the external circulation, leading to vortex nucleation via surface mode excitations. We investigate the vortex nucleation rate for various polarizations of the external driving, where, in particular, we confirm the rotational symmetry breaking due to the chiral spin texture imposed by the magnetic quadrupole field [1]. \\[4pt] [1] J. Choi, et al., Phys. Rev. Lett. 111, 245301 (2013) [Preview Abstract] |
|
Q1.00007: Quantum vortex microscope for observing two-dimensional vortex dynamics in Bose-Einstein condensates Kali Wilson, Joseph Lowney, Brian P. Anderson Laboratory measurements of vortex dynamics in Bose-Einstein condensates (BECs) are essential for the development of a clear understanding of many aspects of superfluid dynamics in these systems. Previously we obtained \texttt{\it in situ} images of a two-dimensional vortex distribution in a single-component BEC using an adaptation of dark-field imaging. Achieving these single-shot \texttt{\it in situ} images is a first step towards observing real-time vortex dynamics in a single BEC. This poster presents the development and implementation of the next phase of our quantum vortex microscope, which will enable the acquisition of multiple \texttt{\it in situ} images of vortices in a single highly oblate BEC. [Preview Abstract] |
|
Q1.00008: Superfluid Atomtronic Circuits Stephen Eckel, Fred Jendrzejewski, Avinash Kumar, Noel Murray, Mark Edwards, Gretchen Campbell We have created a superfluid atom circuit using a toroidal Bose-Einstein Condensate. Just as a current in a superconducting circuit will flow forever, if a current is created in our superfluid circuit, the flow will not decay as long as the current is below a critical value. A repulsive optical barrier across one side of the torus creates a tunable weak link in the condensate circuit and can be used to control the current around the loop. By rotating the weak link, we have observed phase slips between well-defined persistent current states, which are analogous to transitions between flux states in an rf-superconducting quantum interference device (SQUID). We have demonstrated that these transitions are hysteretic. More recently, we have realized a geometry similar to a dc-SQUID using two weak links. In this case, we can move these weak links relative to each other and observe resistive flow when the current exceeds the critical current. This observation of resistive flow is an important step to realizing the atomtronic analog of the dc-SQUID. Lastly, we have developed techniques of measuring the current flow around the ring which allows us to measure the current-phase relationship of our weak link. [Preview Abstract] |
|
Q1.00009: Progress towards a $^{41}$K spinor Bose-Einstein condensate Nathan Holman, Sruti Prathivadhi-Bhayankaram, Lucas Slattery, Alex Tarter, Jonathan Wrubel We report on the progress made in constructing an apparatus to create a potassium-41 Bose-Einstein condensate (BEC) at Creighton University, a primarily undergraduate institution. Several major components of the experiment have been completed including an external-cavity diode laser, laser characterization systems, and the saturated absorption system for laser wavelength locking. Our immediate goals are to complete construction of an atomic source and 2D magneto-optical trap by summer's end. We plan to use this system to study spinor physics in a $^{41}$K BEC. Namely, we will utilize predicted radio-frequency Feshbach resonances to continuously alter the magnetic properties of the system from ferromagnetic to anti-ferromagnetic. Using the radio-frequency Feshbach resonance we aim to explore previously inaccessible magnetic phases and their dynamics. [Preview Abstract] |
|
Q1.00010: Abnormal Superfluid Fraction of Harmonically Trapped Few-Fermion Systems Yangqian Yan, D. Blume Superfluidity is a fascinating phenomenon that, at the macroscopic scale, leads to dissipationless flow and the emergence of vortices. While these macroscopic manifestations of superfluidity are well described by theories that have their origin in Landau's two-fluid model, our microscopic understanding of superfluidity is far from complete. Using analytical and numerical \textit{ab initio} approaches, this paper determines the superfluid fraction and local superfluid density of small harmonically trapped two-component Fermi gases as a function of the interaction strength and temperature. At low temperature, we find that the superfluid fraction is, in certain regions of the parameter space, negative. This counterintuitive finding is traced back to the symmetry of the system's ground state wave function, which gives rise to a diverging quantum moment of inertia $I_{\mathrm{q}}$. Analogous abnormal behavior of $I_{\mathrm{q}}$ has been observed in even-odd nuclei at low temperature. Our predictions can be tested in modern cold atom experiments. [Preview Abstract] |
|
Q1.00011: Characterizing the antiferromagnetic ordering of fermions in a compensated optical lattice P.M. Duarte, R.A. Hart, T.L. Yang, X. Liu, R.G. Hulet, T.C.L. Paiva, D. Huse, R. Scalettar, N. Trivedi We realize the Fermi-Hubbard model with fermionic $^{6}$Li atoms in a three-dimensional, red-detuned optical lattice. The lattice is compensated by the addition of three blue-detuned gaussian beams which overlap each of the lattice laser beams, but are not retro-reflected. Using the compensated lattice potential, we have reached temperatures low enough to produce antiferromagnetic (AF) spin correlations, which we detect via Bragg scattering of light. The variation of the measured AF correlations as a function of the Hubbard interaction strength, $U/t$, provides a way to determine the temperature of the atoms in the lattice by comparison with quantum Monte Carlo calculations. This method suggests our temperature is in the range of 2-3 times the N\'{e}el ordering temperature. In this poster we present our Bragg scattering results along with our studies of the effect of the compensating potential in helping us cool the atoms in the lattice and also enlarge the size of the AF phase.\footnote{C. J. M. Mathy et al., Phys. Rev. A \textbf{86}, 023606 (2011)} [Preview Abstract] |
|
Q1.00012: Arbitrary landscape potentials under Quantum Gas Microscope for probing many-body correlated systems Alexander Lukin, Ruichao Ma, Philipp Preiss, Matthew Rispoli, M. Eric Tai, Rajibul Islam, Markus Greiner We study a low-dimensional system of Rb-87 in an optical lattice under a Quantum Gas Microscope to probe strongly correlated many-body physics with single-site resolution. Controlling the potentials on the single-site level allows us to prepare and probe different many-body quantum states. We achieve such exquisite control over optical potentials using a DMD (digital mirror device) as amplitude grating. This allows for arbitrary beam shaping and compensation for aberrations in the imaging system. We use these techniques to initialize a variety of one-dimensional states and perform a full characterization of the quantum state as well as to study BEC in non-harmonic confining potentials. [Preview Abstract] |
|
Q1.00013: Towards a Quantum Gas Microscope for Ultracold Fermions Matthew Nichols, Lawrence Cheuk, Melih Okan, Vinay Ramasesh, Waseem Bakr, Thomas Lompe, Martin Zwierlein In the past decade ultracold atoms in optical lattices have been established as an ideal model system to study quantum many body physics in a clean and well-controlled environment. Recently, experiments at Harvard and MPQ Munich using bosonic $^{\mathrm{87}}$Rb atoms have made these systems even more powerful by demonstrating the ability to observe and address atoms in optical lattices with single-site resolution. The goal of our experiment is to achieve such single-site resolution for a quantum gas of fermionic atoms. Such local probing would reveal microscopic density or spin correlations which are difficult to extract from bulk measurements. This technique could for example be used to directly observe antiferromagnetic ordering in a fermionic Mott insulator. As the starting point for our experiments we cool fermionic potassium atoms with bosonic sodium as a sympathetic coolant. The atoms are then magnetically transported to an optical trap located ten microns below a solid immersion microscope for high-resolution imaging. In this poster we give a description of our experimental setup and report on our progress towards performing single-site resolved fluorescence imaging of $^{\mathrm{40}}$K atoms trapped in a deep optical lattice. [Preview Abstract] |
|
Q1.00014: Tunable Artificial Graphene with an Ultracold Fermi Gas Daniel Greif, Thomas Uehlinger, Gregor Jotzu, Michael Messer, Remi Desbuquois, Walter Hofstetter, Ulf Bissbort, Tilman Esslinger The engineering of systems that share their key properties with graphene, like Dirac fermions and a hexagonal structure, is gaining interest in an increasing number of disciplines in physics. The motivation for engineering graphene-like band structures is to explore regimes that are not, or not yet, accessible to research with graphene or similar materials. We create an artificial graphene system with tunable interactions by loading a two-component ultracold fermionic quantum gas into an optical lattice with hexagonal structure. We study the crossover from the metallic to the Mott insulating regime for increasing inter-particle interactions. For strong repulsive interactions, we observe a suppression of double occupancy and measure a gapped excitation spectrum. A quantitative comparison between our measurements and theory is additionally presented, making use of a novel numerical method to obtain Wannier functions for complex lattice structures. Furthermore, we will show recent results on alternative methods of accessing insulating phases, for example by controlling the tunneling structure. [Preview Abstract] |
|
Q1.00015: Observation of a low-loss radiofrequency-dressed optical lattice in the tight-binding regime Nathan Lundblad, Edward Moan, Saad Ansari, Yang Guo Traditional optical lattices are limited in length scale to approximately half a wavelength of the lattice laser; the ability to tailor a lattice's periodicity, band structure, and Wannier functions would be a significant aid in using optical lattices to explore analogous solid-state physics. One pathway to lattice modification is the use of radiofrequency dressing to create adiabatic potentials of novel geometry from ``bare'' spin-dependent lattices of traditional geometry. We present measurements made on a one-dimensional radiofrequency-dressed optical lattice in the new regime where the dressed lattice is both tight-binding and long-lived. Momentum distributions, loss rates, and dressed-state spin populations are explored. The bare lattices are sufficiently deep and the rf coupling sufficiently strong such that the adiabatic potentials should prove useful for any experiment exploring novel optical lattice geometries. [Preview Abstract] |
|
Q1.00016: Understanding the role of spin--motion coupling in Ramsey spectroscopy Andrew Koller, Michael Beverland, Joshua Mundinger, Alexey Gorshkov, Ana Maria Rey Ramsey spectroscopy has become a powerful technique for probing non-equilibrium dynamics of internal (pseudospin) degrees of freedom of interacting systems. In many theoretical treatments, the key to understanding the dynamics has been to assume the external (motional) degrees of freedom are decoupled from the pseudospin degrees of freedom. Determining the validity of this approximation -- known as the spin model approximation -- has not been addressed in detail. We shed light in this direction by calculating Ramsey dynamics exactly for two interacting spin-1/2 particles in a harmonic trap. We find that in 1D the spin model assumption works well over a wide range of experimentally-relevant conditions, but can fail at time scales longer than those set by the mean interaction energy. Surprisingly, in 2D a modified version of the spin model is exact to first order in the interaction strength. This analysis is important for a correct interpretation of Ramsey spectroscopy and has broad applications ranging from precision measurements to quantum information and to fundamental probes of many-body systems. [Preview Abstract] |
|
Q1.00017: Phonon Dynamics and Correlation Induced Tunneling of Few-Body Dipolar Bosons in Multiwell Potentials Lushuai Cao, Xiangguo Yin, Peter Schmelcher We numerically investigate the dynamics of few-body dipolar bosonic ensembles in multiwell potentials. Initially the dipolar bosons are prepared in supersolid-like states, with long-range density order and spatial correlations among different sites. A local perturbation is then applied to a single boson, which brings the boson out of equilibrium. We focus on the effect of the non-local dipolar interaction, as well as the site-selected spatial correlation in the initial state to the dynamics. We obtain that firstly, the non-local interaction spread the local perturbation to the whole lattice, and phonon-like collective dynamics arises. Secondly, the site-selected spatial correlation also induces the correlation-induced tunneling (CIT). Moreover the coupling between the phonon dynamics and CIT is also observed. The investigation is based on the numerically exact ML-MCTDHB method, and the results are beyond mean-field approximations and the single-band Bose-Hubbard model. [Preview Abstract] |
|
Q1.00018: Many-body dynamics of the transverse-field Ising model Alexander Pikovski, Johannes Schachenmayer, Ana Maria Rey We investigate the quantum Ising model with a transverse driving field. This model can describe the dynamics of a gas of Rydberg atoms, and also related to systems of cold polar molecules or trapped ions. The time-dependent many-body dynamics of this system is studied using different numerical methods. We compare the results obtained by truncated Wigner approximation, modified cluster expansion, as well as a novel high-order in time expansion method. It is found that the accuracy of the different methods is strongly dependent on the interaction range and the dimensionality of the system. [Preview Abstract] |
|
Q1.00019: Dynamics of out-of-equilibrium domain walls in an ultra-cold Bose gas Jeffrey McGuirk, Dorna Niroomand A gas of $^{87}$Rb atoms does not support spin domains above its critical temperature for degeneracy. However, quantum symmetries during atom-atom collisions can preserve localized spin domains over longer periods of time than would be expected classically, allowing for studies of spin domains in a thermal gas. Here, we create spin domains in a nondegenerate gas using optical patterning techniques. We report progress towards observing the precession of these domains, leading to rapid spin inversions, as well as towards understanding the route to equilibrium. [Preview Abstract] |
|
Q1.00020: Dynamical Defects in Fermi Superfluid Mark Ku, Lawrence Cheuk, Wenjie Ji, Biswaroop Mukherjee, Elmer Sanchez, Tarik Yefsah, Martin Zwierlein We report on the study of dynamical defects in strongly-interacting Fermi superfluids. We create long-lived, solitonic excitations in a trapped Fermi gas of Lithium-6 and directly observe their oscillatory motion. As the interactions are tuned from the regime of Bose-Einstein condensation of tightly bound molecules towards the Bardeen-Cooper-Schrieffer limit of long-range Cooper pairs, the period of the defect is observed to increase markedly. We employ a tomographic imaging technique in which we directly access the local density of our 3D clouds by imaging a thin layer of atoms, achieved with a masked pumping beam that transfers atoms outside of the selected layer into an undetected state. Using the tomographic imaging, which circumvents the density integration along the probing axis, we identify unambiguously this excitation as a solitonic vortex. In particular, we rule out the vortex ring scenario predicted by several theory groups. Our measurements provide a quantitative benchmark for the theories of non-equilibrium dynamics of strongly-interacting superfluids. [Preview Abstract] |
|
Q1.00021: Three-body physics in strongly correlated spinor condensates Victor Colussi, J.P. D'Incao, Chris H. Greene We investigate bosonic spinor condensates in the largely unexplored strongly correlated regime where few-body aspects can play a central role in the properties and dynamics of the system through manifestations of Efimov physics. We have solved the three-body problem using the hyperspherical adiabatic representation, uncovering the multiple, co-existing families of Efimov states and the three-body scattering observables. The presence of these states can lead to non-trivial spin dynamics dominated by three-body correlations as well as the possibility of ultralong lived three-body bound states. The three-body contribution to the mean-field theory is constructed from the scattering observables, and its influence on the various phases of the spinor condensate is considered. [Preview Abstract] |
|
Q1.00022: Photoassociation of ultracold LiRb molecules with short pulses near a Feshbach resonance Marko Gacesa, Subhas Ghosal, Jason Byrd, Robin C\^ot\'e Ultracold diatomic molecules prepared in the lowest ro-vibrational state are a required first step in many experimental studies aimed at investigating the properties of cold quantum matter. We propose a novel approach to produce such molecules in a two-color photoassociation experiment with short pulses performed near a Feshbach resonance. Specifically, we report the results of a theoretical investigation of formation of $^6$Li$^{87}$Rb molecules in a magnetic field. We show that the molecular formation rate can be significantly increased if the pump step is performed near a magnetic Feshbach resonance due to the strong coupling between the energetically open and closed hyperfine states. In addition, the dependence of the nodal structure of the total wave function on the magnetic field allows for enhanced control over the shape and position of the wave packet. The proposed approach is applicable to different systems that have accessible Feshbach resonances. [Preview Abstract] |
|
Q1.00023: Field dependent studies of inelastic scattering properties in an ultracold mixture of lithium and metastable ytterbium Richard Roy, William Dowd, Rajendra Shrestha, Alan Jamison, Alaina Green, Subhadeep Gupta The ultracold mixture of excited state alkaline-earth-like and ground state alkali atoms is a novel system in which to study two-body and few-body physics. Unlike the ground state of ytterbium, the long lived metastable $^3P_2$ state is predicted to support broad magnetic Feshbach resonances with the ground state of lithium, offering a promising route towards the production of ultracold heteronuclear ground state dimers with both magnetic and electric dipole moments. We report on measurements of the field dependence of inelastic scattering properties in this mixture over a wide range of magnetic fields. We also present progress towards a three dimensional optical lattice for the Li-Yb mixture. A tunable optical lattice provides useful tools to control and study collisions in our system, can enhance molecule production efficiency, and can serve as a platform for quantum simulation and information science. Additional potential studies include the use of Yb as an impurity probe of strongly-interacting Li fermions. [Preview Abstract] |
|
Q1.00024: Trapped ion system for simulation of quantum spin models Sylvi Haendel, Danilo Dadic, Michael Ip, Wes Campbell We describe efforts to study and control ordered systems of charged particles and their formation in an ion trap with radial symmetry. The system is realized within a monolithic fused silica design. Using Yb$^+$ ions and an appropriate bichromatic beatnote, an effective spin-spin interaction arises between the clock states of all pairs of $^{171}$Yb$^+$ ions [1,2]. The range and sign of the resulting spin-spin interaction can be controlled through tailoring of the beatnotes. Antiferromagnetic couplings can be generated, allowing the study of highly frustrated magnetism. When simulating frustrated spin system under periodic boundary conditions, the number of ions in the trap plays an important role. For certain trap voltages, ions can crystallize in a 2D planar array in the plane of the RF potential [3]. Nearest-neighbor antiferromagnetic couplings will lead to a highly-frustrated ground state for an odd number of spins. Increasing the number of ions to an even number changes the frustration in the system. We also report on progress with linear RF traps of different architectures. \\[4pt] [1] D. Porras et al., Phys. Rev. Lett. 92, 207902 (2004).\\[0pt] [2] K. Kim et al., Nature 465, 590 (2010).\\[0pt] [3] Itano et al., Proc. Of the Workshop on Crystalline Ion Beams 241-247 (1989). [Preview Abstract] |
|
Q1.00025: Towards Laser Cooling Ions with Telecom Light Steven Olmschenk, Brad Bedacht, Nick Theisen Trapped atomic ions are a proven system in precision measurements, atomic clocks, and quantum information. However, the requirement of ultraviolet or blue light for laser cooling typically results in complex and expensive systems, and may inhibit some applications. We present progress on our proposal to laser cool doubly-ionized lanthanum, requiring only infrared light. In addition to potentially reducing the infrastructure overhead for trapped ion experiments, lanthanum could allow direct interfacing between trapped atomic ions and telecom light, making the system amenable to long-distance quantum communication and distributed quantum computation. [Preview Abstract] |
|
Q1.00026: Anisotropic optical trapping of ultracold erbium atoms Olivier Dulieu, Maxence Lepers, Jean-Francois Wyart We calculate the complex dynamic dipole polarizability of ground-state erbium, a rare-earth atom that was recently Bose-condensed [1]. This quantity determines the trapping conditions of cold atoms in an optical trap. The polarizability is calculated with the sum-over-state formula inherent to second-order perturbation theory. The summation is performed on transition energies and transition dipole moments from ground-state erbium, which are computed using the Racah-Slater least-square fitting procedure provided by the Cowan codes [2]. This allows us to predict several yet unobserved energy levels in the range 25000-31000 cm$^{-1}$ above the ground state. Regarding the trapping potential, we find that ground-state erbium essentially behaves like a spherically-symmetric atom, in spite of its large electronic angular momentum. We find a mostly isotropic van der Waals interaction between two ground-state erbium atoms, with a coefficient C$_{6}^{\mathrm{iso}}=$1760 a.u.. On the contrary, the photon-scattering rate is strongly anisotropic with respect to the polarization of the trapping light [3]. \\[4pt] [1] K. Aikaw et al,. \textit{Phys. Rev. Lett.} \textbf{108}, 210401 (2012).\\[0pt] [2] R.D. Cowan. \textit{The theory of atomic structure and spectra}. University of California Press (1981).\\[0pt] [3] M. Lepers, J.-F. Wyart, and O. Dulieu. \textit{Phys. Rev. A}, in press (2014). [Preview Abstract] |
|
Q1.00027: The Bichromatic Force for Laser Cooling Without Spontaneous Emission Christopher Corder, Brian Arnold, Harold Metcalf The bichromatic force ($F_b$) can produce laser cooling without relying on spontaneous emission (SpE).\footnote{H. Metcalf, Phys. Rev. A {\bf77}, 061401 (2008).} It is implemented with two laser frequencies $\omega_\ell =\omega_a\pm\delta$ where $\omega_a$ is the atomic transition frequency and $\delta$ is a detuning, $\delta\gg\gamma =1/\tau$ where $\tau$ is the excited atomic state lifetime. This produces multiple absorption-stimulated emission cycles to cause many momentum exchanges on a timescale faster than $\tau$. The resulting magnitude of $F_b=2\hbar k\delta /\pi$ is much larger than the radiative optical force ($\hbar k\gamma/2$) and spans a much larger velocity range ($\Delta v_b=\delta /2k$). Previous measurements have demonstrated $F_b$ over time scales that included many SpE events.\footnote{M. Partlow et al., Phys. Rev. Lett. {\bf93}, 213004 (2004).} We have made measurements with a $F_b$ cooling time ($M\Delta v_b/F_b$) that is on the order of $\tau$, thus having zero or at most one SpE during the experimental interaction time. Our intensity dependent studies show the atomic velocities changing over a range of many atomic recoils and accumulating at the edge of the $F_b$ velocity profile, and we have developed numerical simulations that corroborate these results. [Preview Abstract] |
|
Q1.00028: Study of the Efficiency of STIRAP Yuan Sun, Vladislav Zakharov, Harold Metcalf We measure the efficiency of the STIRAP process in exciting 2$^3$S metastable He atoms (He*) to Rydberg states. Atoms in a beam are excited to 3$^3$P by $\lambda =$ 389 nm light (blue), and from there to Rydberg states by $\sim 800$ nm (red) light. The parallel laser beams are perpendicular to the atomic beam, arranged so that the atoms encounter the red light first (in counterintuitive order), partially overlapping with the blue. Although the lasers are CW, the atoms fly through their mm-size beams at $v \sim$ 1070 m/s so they see $\mu$s pulses of light. The primary detection scheme uses a stainless steel detector (SSD) as a target from which He* can efficiently eject an electron. A bichromatic light beam at $\lambda =$ 1083 nm exerts a strong transverse force on He* atoms that deflects them into the offset SSD, but Rydberg atoms are unaffected, thus allowing an absolute measure of the Rydberg atoms. A secondary detection method exploits the relative ease of ionizing Rydberg atoms by background blackbody radiation. The efficiency of Rydberg production is partly limited by the residual transverse velocity spread of the atomic beam, causing Doppler broadening. This will be partially remedied with an optical molasses for transverse cooling just before the STIRAP region. [Preview Abstract] |
|
Q1.00029: On the basis size problem in ultracold molecular scattering: Approximate hyperfine cross sections from hyperfine-free calculations Maykel Leonardo Gonzalez-Martinez Understanding (ultra)cold collisions is crucial to assess both the prospects of cooling techniques that rely on thermalization and trapping lifetimes. However, brute-force application of the coupled-channel method to many low-temperature scattering problems finds two main obstacles: (1) the need for large basis sets that are computationally intractable, and (2) the need to explore a multidimensional parametric space in order to tackle questions concerning real experimental conditions. The basis size problem arises because many interactions that are negligible at thermal temperatures become comparable to, or larger than, the collision energies involved. Taking all such terms into account significantly increases the size of the basis needed for convergence, with dramatic effects on the computing effort. Here, I discuss an approximate method to account for the effect of hyperfine interactions in ultracold molecular scattering. The method naturally resolves the effects discussed by Gonzalez-Martinez and Hutson in calculations on Mg+NH, and may be combined with those by Tscherbul et al. and Croft et al. to tackle problems which are computationally intractable to date. Depending on the system, the proposed method may lead to one to four orders-of-magnitude savings in computing times. [Preview Abstract] |
|
Q1.00030: A new apparatus for the manipulation of polar KRb molecules Jacob Covey, Bo Yan, Steven Moses, Bryce Gadway, Deborah Jin, Jun Ye Long-range dipolar interactions can facilitate understanding of strongly interacting many-body quantum systems with phenomena such as quantum magnetism. While we have used polar molecules pinned in a three-dimensional optical lattice to realize a spin-exchange model, the absence of an external electric field precluded the study of the full spin-1/2 Hamiltonian that includes the Ising interaction. Moreover, manipulation of dipolar properties of a bulk molecular gas is also desired. We report on progress towards the second generation of our KRb polar molecule apparatus that will allow for large electric fields with the flexibility to apply gradients of the field in arbitrary directions. The same electrodes that supply large DC electric fields can also provide AC fields for driving rotational transitions to encode spin, where the relative angle between the AC and DC fields can be tuned to control the polarization of the microwave field. Moreover, the geometry of the system is amenable to high resolution optical detection of the molecules. We plan to implement these tools to perform dipolar evaporative cooling of our spin-polarized fermionic molecular gas. [Preview Abstract] |
|
Q1.00031: Towards Fermionic Ground State Molecules with Strong Dipolar Interactions Sebastian Will, Jee Woo Park, Cheng-Hsun Wu, Jennifer Schloss, Qingyang Wang, Martin Zwierlein A degenerate Fermi gas with strong dipolar interactions should enable the creation of novel states of matter such as quantum crystals, supersolids and topological superfluids. Fermionic ground state molecules are promising candidates for the experimental realization of such a dipolar Fermi gas, as they can have a large electric dipole moment that gives rise to long-range anisotropic interactions. ${}^{23}$Na${}^{40}$K is a fermionic molecule that is especially well suited for this purpose. In its rovibrational ground state, it is chemically stable against molecule-molecule collisions and possesses a large electric dipole moment of 2.72 Debye. We have found that ${}^{23}$Na${}^{40}$K Feshbach molecules have a long lifetime and a significant admixture of the electronic spin singlet state. Therefore, they constitute an ideal starting point to reach the singlet rovibrational ground state in a two-photon STIRAP process. We have spectroscopically explored excited and ground state molecular potentials of ${}^{23}$Na${}^{40}$K and successfully performed STIRAP transfer into a deeply bound vibrational level. [Preview Abstract] |
|
Q1.00032: Synthetic $p$-wave scattering in a degenerate Fermi gas Benjamin Stuhl, Lauren Aycock, Dina Genkina, Ian Spielman $P$-wave superfluids are fascinating for a number of reasons; perhaps the most notable of these is their ability to support Majorana-type excitations [1]. Unfortunately, attempts to use $p$-wave Feshbach resonances to produce superfluid states in ultracold, fermionic gases have substantially failed due to to the large inelastic loss rates associated with those resonances [2,3]. We demonstrate a new approach to the problem: we use optical Raman dressing to artificially engineer the scattering properties. This allows us to convert the scattering strength of an $s$-wave Feshbach resonance into a strong $p$-wave interaction in an ultracold gas of $^{40}$K atoms. Our prior success in engineering $d$- and $g$-wave scattering in a degenerate Bose gas [4] is strong evidence for the viability of this technique. \\[4pt] [1] V. Gurarie and L. Radzihovsky, \textit{Phys. Rev. B} \textbf{75}, 212509 (2007). \\[0pt] [2] C. Chin, et al., \textit{Rev. Mod. Phys.} \textbf{82}, 1225 (2010). \\[0pt] [3] C. A. Regal, et al., \textit{Phys. Rev. Lett.} \textbf{90}, 053201 (2003). \\[0pt] [4] R. A. Williams, et al., \textit{Science} 335, 314 (2012). [Preview Abstract] |
|
Q1.00033: Experimental studies of excitations in a BEC in light-induced gauge fields Chuan-Hsun Li, David Blasing, Abraham Olson, Robert Niffenegger, Yong P. Chen We present our experimental studies of various excitation processes in a $^{87}$Rb Bose-Einstein condensate (BEC) in the presence of Raman light-induced gauge fields. We have systematically studied controllable inter-band excitations by modulating the strength of the Raman coupling, and probed the resultant decay from the upper dressed bands and heating of the BEC. We also present preliminary results probing the effects of synthetic spin-orbit coupling and gauge fields on collective excitations as well as photoassociation processes in the BEC. [Preview Abstract] |
|
Q1.00034: ATOMIC AND MOLECULAR COLLISIONS |
|
Q1.00035: Hybrid theory of $D$-wave electron-hydrogenic systems and photoabsorption in two-electron systems A.K. Bhatia A variational wave function incorporating short range correlations via Hylleraas type functions plus long-range polarization terms of the polarized orbital type but with smooth cut-off factors has been used to calculate D-wave phase shifts for electron scattering from H, He$^{\mathrm{+}}$, and Li$^{\mathrm{+2}}$. This approach gives the direct r$^{\mathrm{-4}}$ potential and a non-local optical potential which is negative definite. The resulting phase shifts have rigorous lower bonds and the convergence is much faster than those obtained without the modification of the target function. The continuum functions obtained for the $D$- and S-waves have been used to calculate photoabsorption cross sections of the $P$ states in He, and Li$^{\mathrm{+}}$. These cross sections have been used to calculate recombination rate coefficients. Final results will be presented at the conference. [Preview Abstract] |
|
Q1.00036: Theoretical Studies of Dissociative Recombination of Electrons with SH$^+$ Ions D.O. Kashinski, O.E. Di Nallo, A.P. Hickman, D. Talbi We are investigating the dissociative recombination (DR) of electrons with the molecular ion SH$^+$. (The process is $e^- + \mathrm{SH}^+ \rightarrow \mathrm{S + H}$.) SH$^+$ is found in the interstellar medium (ISM), and little is known concerning its interstellar chemistry. The abundance of SH$^+$ in the ISM suggests that destruction processes, like DR, are inefficient. Understanding the role of DR as a destruction pathway for SH$^+$ will lead to more accurate astrophysical models. We are currently performing large scale multi-reference configuration interaction (MRCI) electronic structure calculations to obtain excited-state potential energy curves (PECs) of SH. PECs have been calculated at several different values of the SH separation. This preliminary work shows that low Rydberg states strongly interact with excited valence states and suggests that highly excited Rydberg states might be critically important. Currently we are expanding the active space of the MRCI calculations in order to assess the importance of these excited Rydberg states. The block diagonalization method will be used to disentangle interacting states forming a diabatic representation of the PECs. The current status of the work will be presented at the conference. [Preview Abstract] |
|
Q1.00037: Vortices for K-shell ionization of carbon by electron impact S.J. Ward, J.H. Macek Using the Coulomb-Born approximation [1], we obtained a deep minimum in the TDCS for K-shell ionization of carbon by electron impact [2,3]. The minimum is due to a vortex in the velocity field [2,3]. We considered the electron to be ejected in the scattering plane, which we took to be the $xz$-plane. The minimum was obtained for the kinematics of an incident energy $E_i = 1801.2\,eV$, scattering angle $\theta_f = 4^\circ$, energy of ejected electron $E_k = 5.5\,eV$, and angle of the ejected electron $\theta_k = 239^\circ$. We analyzed the importance of various multipole components in an expansion of the Coulomb-Born T-matrix [1,3]. We also considered the electron ejected out of the scattering plane for $E_i = 1801.2\,eV$ and $\theta_f = 4^\circ$ and located the positions of vortices for small but nonzero values of $k_y$, the $y-$component of the momentum of the ejected electron [2]. We constructed the vortex line for the kinematics of $E_i = 1801.2\,eV$ and $\theta_f = 4^\circ$.\\[4pt] [1] J. Botero and J. H. Macek, Phys. Rev. A {\bf 45}, 154 (1992).\\[0pt] [2] S. J. Ward and J. H. Macek, http://meetings.aps.org/link/BAPS.2011.DAMOP.Q1.63.\\[0pt] [3] S. J. Ward and J. H. Macek, Bull. Am. Phys. Soc. {\bf 58}, no. 6, p. 61 (2013), http://meetings.aps.org/link/BAPS.2013.GEC.HW1.19. [Preview Abstract] |
|
Q1.00038: Metastable Atom Detection Using Solid N$_{2}$ William McConkey, Wladek Kedzierski, Dragan Lukic Over the years our laboratory has been a center for the use of rare-gas matrices at temperatures below 70K in the detection and study of low energy atomic and molecular metastable particles [see Kedzierski et al, Can J Phys, 91, 1044, (2013) for Refs]. Recently we have extended this work to study the use of a solid nitrogen matrix at temperatures below 35K as a detector of O($^{1}$S) atoms. This proves to be at least as sensitive as any rare gas matrix though the lifetime of the excimer formed in the matrix is somewhat longer ($\sim$ 20 $\mu$s) than what is observed in a Xe matrix for example. The detailed performance of the detector as a function of temperature and other parameters will be presented at the conference. [Preview Abstract] |
|
Q1.00039: Dissociative Excitation of Thymine by Electron Impact William McConkey, Collin Tiessen, Jeffrey Hein, Joshuah Trocchi, Wladek Kedzierski A crossed electron-gas beam system coupled to a VUV spectrometer has been used to investigate the dissociation of thymine (C$_{5}$H$_{6}$N$_{2}$O$_{2})$ into excited atomic fragments in the electron-impact energy range from threshold to 375 eV. A special stainless steel oven is used to vaporize the thymine and form it into a beam where it is intersected by a magnetically collimated electron beam, typical current 50 $\mu$A. The main features in the spectrum are the H Lyman series lines. The probability of extracting excited C or N atoms from the ring is shown to be very small. In addition to spectral data, excitation probability curves as a function of electron energy will be presented for the main emission features. Possible dissociation channels and excitation mechanisms in the parent molecule will be discussed. [Preview Abstract] |
|
Q1.00040: Chirally-Sensitive Electron-Induced Molecular Breakup Joan Dreiling, Timothy Gay We present the results of our search for asymmetric interactions between longitudinally spin-polarized electrons and chiral bromocamphor (C$_{10}$H$_{15}$BrO) molecules. We define the asymmetry as $A = $[($I\uparrow $-$I\downarrow )$/($I\uparrow +I\downarrow )$]$_{L}$-[($I\uparrow $-$I\downarrow )$/($I\uparrow +I\downarrow )$]$_{R}$, where $I\uparrow $ ($I\downarrow )$ is the current measured for spin-up (spin-down) electrons and the ``$L$'' and ``$R$'' subscripts correspond to the left- and right-handed chirality of the molecules. Two electron-molecule interaction channels were studied: electron transmission (related to the total scattering cross section) and dissociative electron attachment (DEA). The asymmetry results for the transmitted current of longitudinally spin-polarized electrons through a vapor of chirally-pure bromocamphor molecules are compared to those of Mayer \textit{et al.} [1]. We have also measured an asymmetric DEA cross section by detecting Br$^{-}$ ions. Observation of this effect represents evidence of chirally-sensitive molecular breakup. \\[4pt] [1] S. Mayer, C. Nolting, and J. Kessler, J. Phys. B \textbf{29}, 3497 (1996). [Preview Abstract] |
|
Q1.00041: Complex-Kohn Approach to Molecular Ionization by High-Energy Electrons: Application to H$_2$, H$_2$O and CH$_4$ Chih-Yuan Lin, C.W. McCurdy, T.N. Rescigno The complex Kohn variational method, which has been extensively applied to low-energy molecule scattering, is extended to treat molecular ionization by fast electrons under the assumption that the incident and scattered electrons can be described by plane-waves. In contrast to other perturbative approches, the interaction between the slow ejected electron and the residual molecular ion is treated by a close-coupling method and for that we employ the complex Kohn variational method. The formulation reduces to the computation of the continuum generalized oscillation strength, which amounts to a generalization of the molecular photoionization problem to which the Kohn method has been successfully applied. The essential point is that the use of a correct electron-ion scattering wave function as the final state for the ejected electron enables us to treat high-energy electron impact ionization of molecules at the same level of sophistication achieved for atomic targets. We will present fully differential cross sections for ionization of water and methane, as well as for excitation/ionization of H$_2$, along with comparisons to available experimental data. [Preview Abstract] |
|
Q1.00042: Electron elastic scattering off $A$@C$_{60}$ fullerenes: the ``zeroth-order'' trends M. Hunter, M. Cooper, C. Bayens, V. Dolmatov The theoretically revealed trends in electron elastic scattering off endohedral fullerenes A@C$_{60}$ associated with the nature of an encapsulated atom A, its size and spin (A = Ar, Xe, Ba, Cr and Mn) are highlighted. It is shown that placing an atom A inside the C$_{60}$ cage can make electron scattering off A@C$_{60}$ weaker than off the empty C$_{60}$ cage, especially when the encapsulated atom A donates an appreciable part of its electron density to the C$_{60}$ cage, as do Ba, Cr and Mn. It is shown that, for such atoms, $\rm e$ $+$ A@C$_{60}$ scattering can even be weaker than off the isolated atom A itself. In addition, if such encapsulated atom has also a nonzero spin $S$ (Cr's $S=3$, Mn's $S=5/2$), then the C$_{60}$ cage can become ``spin-charged''; this results in a strong electron spin-dependence of $\rm e$ $+$ A@C$_{60}$ scattering. In calculations, (a) electron correlation was ignored, (b) both the encapsulated atom A and C$_{60}$ cage were regarded as non-polarizable targets, and (c) the C$_{60}$ cage was modeled by a spherical annular well. Results, thus, provide the understanding of $\rm e$ $+$ A@C$_{60}$ scattering in a ``zeroth-order'' approximation and, most likely, identify some of the most intrinsic properties of $\rm e$ $+$ A@C$_{60}$ elastic scattering. [Preview Abstract] |
|
Q1.00043: Recent developments in theoretical treatment of dissociative recombination Viatcheslav Kokoouline, Nicolas Douguet, Samantha Fonseca dos Santos, Ann Orel Over last few years, we have been developing a theoretical treatment of dissociative recombination (DR), which can be general and simple enough to be applied to a wide range of small polyatomic ions. In this work we present such a approach, which is based on the first principles only. It relies on the scattering matrix calculations for electron-ion collisions performed for fixed nuclei for a number of geometries near the equilibrium position of the ion. The obtained geometry-dependent scattering matrix is then used to calculate the cross section for electron capture into a Rydberg state of an excited vibrational mode of the molecule. This is made by a standard vibrational frame transformation from the molecular to laboratory frame. Assuming that the autoionization of such Rydberg states is much slower than predissociation, the electron capture cross section gives approximately the DR cross section. We will give two examples of such DR calculations, for the HCO$^+$, N$_2$H$^+$ ions. The obtained theoretical DR cross sections agree well with available experimental results. [Preview Abstract] |
|
Q1.00044: ABSTRACT WITHDRAWN |
|
Q1.00045: Differential Cross Sections for Charge Transfer in Collisions between Protons and the Ions He$^+$, Li$^{2+}$, Be$^{3+}$, B$^{4+}$, and C$^{5+}$ Thomas Winter Coupled-state differential cross sections are being determined for electron transfer in collisions between keV-energy protons and the hydrogenic ions He$^+$, Li$^{2+}$, Be$^{3+}$, B$^{4+}$, and C$^{5+}$. Integrated cross sections for these five collisional systems using a two-center, coupled-Sturmian-pseudostate approach have been recently reported.\footnote{T. G. Winter, Phys. Rev. A {\bf 87}, 032704 (2013).} Differential cross sections were previously considered for He$^+$ targets only; those calculations used smaller two-center Sturmian bases, as well as triple-center, atomic-state bases.\footnote{T. G. Winter, Phys. Rev. A {\bf 49}, 1767 (1994).} In the eikonal approach taken in that and earlier papers,\footnote{L. Wilets and S. J. Wallace, Phys. Rev. {\bf 169}, 84 (1968).} the differential cross sections were obtained by integrating the transition amplitude from the scattering calculation over impact parameter after multiplying by a suitable energy phase and a Bessel function. A simpler approach, also taken, was just to multiply the square of the transition amplitude at the classical scattering angle corresponding to the impact parameter by the Rutherford scattering cross section, an approach probably valid at large scattering angles and small impact parameters. [Preview Abstract] |
|
Q1.00046: Portable three-dimensional imaging for an explicit identification of the internal state of diatomic molecular ions V.M. Andrianarijaona, C. Alaime, B. Fabre, A.K. Vassantachart, J.J. Jureta, X. Urbain A transportable experimental set-up was developed at the Universit\'{e} catholique de Louvain in Louvain-la-Neuve, Belgium to measure the internal energies of small diatomic molecular ions such as H$_{2}^{+}$. The technique, which scheme was first developed by D. P. de Bruijn and J. Los (Rev. Sci. Intstrum. 53, 1020, 1982) and included a resonant dissociative charge exchange with alkali atoms, consists in measuring the positions of the fragments and their flight time difference with two position sensitive detectors. The measured kinetic energy release is directly related to the original level of vibrational excitation of H$_{2}^{+}$. Details and applications will be presented. [Preview Abstract] |
|
Q1.00047: Line ratios of soft x-ray emissions following charge exchange between C$^{6+}$ and Kr C.I. Guillen, S.L. Romano, V.M. Andrianarijaona, D. McCammon, M. Fogle, D.G. Seely, C.C. Havener The radiance line ratios (Ly-$\beta $ thru -$\varepsilon $ over Ly-$\alpha )$ for soft x-ray emission following charge exchange between C$^{\mathrm{6+}}$ and Kr are reported for collision velocities between 250 and 3000 km/s, which are characteristic of the solar wind. The spectra were measured at the Oak Ridge National Laboratory ion-atom merged beams apparatus equipped with a 10 eV FWHM resolution x-ray detector. A crossing between the measured Ly-$\beta $/Ly-$\alpha $ and Ly-$\gamma $/Ly-$\alpha $ is well resolved around 950 km/s and could be used as a velocity indicative tool. There is no Kr theory, but Kr has the same ionization potential as H so that the results reported here are compared to calculations done on C$^{\mathrm{6+}}+$H. On the other side, double-electron-capture is possible for this system and for any multi-electron target. True double capture is seen to be only 10{\%} of the single-electron-capture. This research is supported in part by the NASA Solar \& Heliospheric Physics Program NNH07ZDA001N, NASA Grant No. NNX09AF09G, by the Office of Fusion Energy Sciences and the Office of Basic Energy Sciences of the U.S. Department of Energy, and by the National Science Foundation through Grant No. PHY-106887. [Preview Abstract] |
|
Q1.00048: ABSTRACT WITHDRAWN |
|
Q1.00049: Quantum-mechanical study of ionization and capture in proton-methane collisions Arash Salehzadeh, Tom Kirchner A recently developed method for first-principles calculations of electron removal from multicenter molecules subjected to ion impact [1] is applied to the proton-methane collision system in the 20 keV to few MeV energy regime. As in our previous work involving water molecules we use a spectral representation of the molecular Hamiltonian and a single-center expansion of the initially populated molecular orbitals to make the problem amenable to the two-center basis generator method for the solution of the time-dependent single-particle equations. Results for (net) capture and ionization are compared with available experimental data and with results obtained from the simple Bragg additivity rule according to which the molecular cross sections are obtained from adding atomic ones. We observe good overall agreement at high energies. At low and intermediate energies the situation is less clear: While our molecular method clearly outperforms the Bragg rule for capture, the latter seems to fare better in the case of ionization. A detailed comparison and analysis will be presented at the conference.\\[4pt] [1] M. Murakami \textit{et al.}, Phys. Rev. A \textbf{85}, 052704 (2012). [Preview Abstract] |
|
Q1.00050: Independent-particle and independent-event calculations for 1.5 MeV/amu O$^{8+}$-Li collisions Laszlo Gulyas, Nariman Khazai, Tom Kirchner In a recent experiment, ionization in 1.5 MeV/amu O$^{8+}$-Li collisions was considered [1]. The measured spectra exhibit two distinct peaks, which were identified as being due to the removal of the $2s$- and the removal of one of the $1s$-electrons, respectively. Since a continuum-distorted wave with eikonal initial state (CDW-EIS) calculation for Li($1s$) ionization did not agree with the measured electron-energy differential cross section associated with the second peak, it was concluded that it may be due to a two-electron excitation-ionization process not accounted for in the calculation. In order to test this interpretation we have combined single-particle CDW-EIS calculations for ionization with basis generator method calculations for excitation using both independent-particle and independent-event models. We find that the proposed two-electron process, in which a $1s$ electron is promoted to an excited state while the $2s$ electron is ionized, does contribute, but cannot fully explain the experimental cross section. Rather, one has to consider the sum of various processes in which a vacancy is created in the Li $K$-shell to obtainaccebtable agreement with the data.\\[4pt] [1] D. Fischer {\it et al.}, Phys. Rev. Lett. \textbf{109}, 113202 (2012). [Preview Abstract] |
|
Q1.00051: Measurements of ion-atom collision rates within a hybrid trap Douglas Goodman, James Wells, Frank Narducci, Winthrop Smith The realization of hybrid ion-neutral traps has increased experimental and theoretical interest in cold collisions between atomic or molecular ions and neutral atoms. Due to the polariziblity of the neutral alkali species, ion-atom collisions can have large elastic and charge-exchange scattering cross sections ($\sim10^6$ a.u.) compared to neutral collisions ($\sim 1$ a.u.). Experimental measurements of these collisions rates as a function of collision energy and the initial atomic states of the colliding partners are of great interest to astrophysics, quantum information, and theoretical atomic physics. The hybrid trap used by our group consists of a sodium (Na) MOT concentric with the center of a linear rf quadrupole ion trap containing sodium or calcium (Ca$^+$) ions. We present preliminary ``dark" measurements of the total collision rate (both charge exchange and elastic) between Na$^+$ and Na, as well as measurements of the charge exchange rate between Ca$^+$ and Na. [Preview Abstract] |
|
Q1.00052: An investigation of resonances in $e^{+}$-H scattering embedded in Debye plasmas Ye Ning, Z.-C. Yan, Y.K. Ho We have carried out calculations for $S$-wave and $P$-wave resonances in $e^{\mathrm{+}}$-H scattering in weakly coupled Debye plasmas in which the interacting potential between two charge particles is represented by a screened Coulomb potential. We have employed the complex-scaling method [1] with Hylleraas-type wave functions to take into account of the correlation effects. In the complex-scaling treatment of the screened Coulomb potential, we first performed a Taylor series expansion for the exponential function that contains the ``$r_{\mathrm{ij}}$'' factor into a polynomial with various powers ($r_{\mathrm{ij}})^{\mathrm{n}}$. Then complex transformation with $r_{\mathrm{ij}}\to r_{\mathrm{ij}}$ \textit{exp}(i$\theta$) for such a series was subsequently carried out, and resonance complex eigenvalues were deduced from their stabilization with respect to the changes of rotational angles $\theta $, and with respect to the changes of some parameters in the wave functions (see [2] for more details). For $S$-wave resonances, reasonably good agreement has been found with earlier calculations using different methods [3, 4]. Some new results for the $P$-wave resonances will be presented at the meeting.\\[4pt] [1] Y. K. Ho\textit{, Phys. Rept.} \textbf{99}, 1, (1983), and references therein;\\[0pt] [2] L.-G. Jiao and Y. K. Ho, \textit{Phys. Plasmas} \textbf{20}, 083303 (2013);\\[0pt] [3] S. Kar and Y. K. Ho, \textit{J. Phys. B} \textbf{38}, 3299 (2005);\\[0pt] [4] S. Chakraborty and Y. K. Ho, \textit{Phys. Rev. A }\textbf{77}, 014502 (2008). [Preview Abstract] |
|
Q1.00053: Modeling enhancement and suppression of vibrational Feshbach resonances in positron annihilation on molecules J.R. Danielson, M.R. Natisin, A.C.L. Jones, C.M. Surko Experiments have shown that positrons can attach to molecules via vibrational Feshbach resonances,\footnote{G. F. Gribakin, et al., {\it Rev. Mod. Phys.} {\bf 82}, 2557 (2010).} leading to increased annihilation rates, the magnitudes of which depends upon molecular structure.\footnote{A. C. L. Jones, et. al., {\it Phys. Rev. Lett.} {\bf 110}, 223201 (2013).} Presented here is a simplified rate-equation model that has recently been constructed to describe the competition between annihilation while the positron is attached to the molecule, positron ejection from the entrance state, and diffusion of the vibrational energy to multimode states followed by similar ejection due to vibrational deexcitation.\footnote{J. R. Danielson, et. al., {\it Phys. Rev. A} {\bf 88}, 062702 (2013).} The latter process can lead to either suppression or enhancement of the annihilation depending on whether the coupled vibrations are more strongly or weakly coupled to the positron continuum. This model elucidates the role that mode coupling can play in determining resonant annihilation amplitudes. Simple limits are obtained and compared with experimental results for selected molecules. [Preview Abstract] |
|
Q1.00054: Positron cooling by vibrational and rotational excitation of a molecular gas Mike Natisin, James Danielson, Cliff Surko A better understanding of low energy positron-molecule collisions and thermalization processes will aid in the development of novel experimental techniques and technology. In particular, cryogenic positron plasmas would allow the creation of positron beams with significantly higher energy resolution than currently available, enabling the study of scattering features and annihilation processes not measurable using current techniques.\footnote{A. C. L. Jones et al., {\it Phys. Rev. Lett.} {\bf 108}, 093201 (2010).} Measurements of positron temperature as a function of time are presented when a positron gas, confined in an electromagnetic trap at an elevated temperature ($\geq1200$~K), is cooled by interactions with the 300~K molecular gases CF$_4$, N$_2$ and CO. A simple model describing positron thermalization by coupling to vibrational and rotational modes is also presented and used to make cooling-rate predictions calculated in the Born approximation. Comparisons to the measured positron cooling-rate curves permit estimates of the magnitudes of the relevant cross sections. Positron cooling rates are compared for these gases at 300~K, and estimates of their effectiveness in cooling positrons to cryogenic temperatures is discussed. [Preview Abstract] |
|
Q1.00055: Positronium-hydrogen scattering for the first six partial waves Denton Woods, P. Van Reeth, S.J. Ward We have performed Kohn variational calculations for the S-, P- and D-waves of positronium-hydrogen scattering using elaborate trial wavefunctions which contains a large number of Hylleraas-type terms for the short-range part [1]. The trial wavefunctions include all 6 interparticle coordinates. The $^{1,3}$S, $^{1,3}$P and $^{1}$D phase shifts compare well with close-coupling results [2,3], but the $^{3}$D phase shifts are appreciably lower. We are investigating improving the accuracy of the $^{3}$D phase shifts using a variety of techniques. In addition, we have preliminary Kohn variational data for the F-, G- and H-wave with fewer short-range terms. \\[4pt] [1] Denton Woods, P. Van Reeth and S.J. Ward, http://meetings.aps.org/Meeting/MAR14/Event/215763 (and references within).\\[0pt] [2] Jennifer E. Blackwood, Mary T. McAlinden and H.R.J. Walters, Phys.~Rev.~A, {\bf 65}, 032517-1 (2002).\\[0pt] [3] H.R.J. Walters, A.C.H. Yu, S. Sahoo and Sharon Gilmore, Nucl. Instrum. and Methods Phys.~Res. B {\bf 221}, 149 (2004). [Preview Abstract] |
|
Q1.00056: Positron Scattering from Argon Dennis Mueller, Simon Armitage, Roisin Boadle, Alexander Dorn, Stephen Buckman, James Sullivan Positron scattering from atomic and molecular targets differs significantly from electron scattering. While the induced target polarization is similar for the two projectiles, the repulsive nature of the positron interaction with the nuclei significantly modifies the potential experienced by this positively charged projectile. In addition, for ionizing interactions the post collision interaction between the positron and ejected electron differs significantly from electron impact ionization. The experiments described here probe these differences with the goal of measuring the final state momentum of each particle, scattered positron, ejected electron and resulting ion. The current status of these experiments will be presented. [Preview Abstract] |
|
Q1.00057: Complex-scaling of screened Coulomb potentials for resonance calculations utilizing the modified Bessel functions Li-Guang Jiao, Yew Kam Ho The screened Coulomb potential (SCP) has been extensively used in atomic physics, nuclear physics, quantum chemistry and plasma physics. However, an accurate calculation for atomic resonances under SCP is still a challenging task for various methods. Within the complex-scaling [1] computational scheme, we have developed a method utilizing the modified Bessel functions to calculate doubly-excited resonances in two-electron atomic systems with configuration interaction-type basis. To test the validity of our method, we have calculated $S$- and $P$-wave resonance states of the helium atom with various screening strengths, and have found good agreement with earlier calculations using different methods [2, 3]. Our present method can be applied to calculate high-lying resonances associated with high excitation thresholds of the He$^{+}$ ion, and with high-angular-momentum states. The derivation and calculation details of our present investigation together with new results of high-angular-momentum states will be presented at the meeting.\\[4pt] [1] Y. K. Ho,\textit{ Phys. Rept. }\textbf{99}, 1 (1983), and references therein;\\[0pt] [2] S. Kar and Y. K. Ho, \textit{Phys. Rev. A} \textbf{72}, 010703 (2005);\\[0pt] [3] S Chakraborty and Y. K. Ho, \textit{Eur Phys. J. D} \textbf{49}, 59 (2008) [Preview Abstract] |
|
Q1.00058: Triply-excited auto-dissociating resonant states in the positron-helium system Y.K. Ho, Ye Ning, Z.-C. Yan An example of triply-excited auto-dissociating resonant states in the positron-helium system is when a positron is bound by the doubly-excited 2$s^{\mathrm{2}} \quad^{\mathrm{1}}S^{\mathrm{e}}$ state of the helium atom, in a manner similar to that in the positronium-hydrogen system when a positron is bound to the doubly-excited 2$s^{\mathrm{2}}$ $^{\mathrm{1}}S^{\mathrm{e}}$ state of the H$^{\mathrm{-}}$ ion [1]. As such states are located in the scattering continua, they would manifest themselves as resonances in positron helium and positronium hydrogen scattering, respectively. In the present work, we have carried out calculations for triply-excited resonances in positron helium scattering. Resonance parameters (both resonance position and width) for some $S$-wave resonances were obtained by using the method of complex-coordinate rotation [2], and with employing elaborated Hylleraas-type wave functions in which all six inter-particle coordinates were included (see [3], for example). For the e$^{\mathrm{+}}$He(2$s^{\mathrm{2}} \quad^{\mathrm{1}}S^{\mathrm{e}})$ and e$^{\mathrm{+}}$He(3$s^{\mathrm{2}} \quad^{\mathrm{1}}S^{\mathrm{e}})$ resonances, a comparison for our results with those in the literature is made [4]. We have also found some new $S$-wave resonances that have not been reported in the literature, and our recent findings will be presented at the meeting.\\[4pt] [1] Y. K. Ho, \textit{Phys. Rev. A} \textbf{41}, 68 (1990);\\[0pt] [2] Y. K. Ho\textit{, Phys. Rept.} \textbf{99}, 1, (1983), and references therein;\\[0pt] [3] Z.-C. Yan and Y. K. Ho,\textit{ Phys. Rev. A} \textbf{59}, 2697 (1999);\\[0pt] [4] J. Mitroy and J. Grineviciute, \textit{Phys. Rev. A} \textbf{88}, 022710 (2013). [Preview Abstract] |
|
Q1.00059: Neutron-Impact Ionization of H and He T.-G. Lee, M.F. Ciappina, F. Robicheaux, M.S. Pindzola Perturbative distorted-wave and non-perturbative close-coupling methods are used to study neutron-impact ionization of H and He. For single ionization of H, we find excellent agreement between the distorted-wave and close-coupling results at all incident energies. For double ionization of He, we find poor agreement between the distorted-wave and close-coupling results, except at the highest incident energies. We present the ratio of double to single ionization for He as a guide to experimental checks of theory at low energies and experimental confirmation of the rapid rise of the ratio at high energies. [Preview Abstract] |
|
Q1.00060: Progress towards a measurement of the electron electric dipole moment with trapped molecular ions Will Cairncross, Kevin Cossel, Matt Grau, Dan Gresh, Jun Ye, Eric Cornell Trapped molecular ions are well suited to searches for the electric dipole moment of the electron (eEDM) due to the long coherence times possible. The current experiment at JILA focuses on the metastable $^3\Delta_1$ level of HfF$^+$ in a Paul trap with additional rotating electric and magnetic bias fields. We have demonstrated the ability to state-selectively transfer population to the desired $^3\Delta_1$ $J = 1$ state in the ion trap and to efficiently read-out the population in single spin states using photodissociation. Using these techniques, we performed Stark spectroscopy of the eEDM measurement states and made an absolute determination of the magnetic g-factors of the $m_F = \pm3/2$ Zeeman sub-levels. Finally, we have demonstrated eEDM-sensitive Ramsey spectroscopy in a rotating bias field with 100 ms coherence time and four detected ion counts on average per experimental cycle. [Preview Abstract] |
|
Q1.00061: PRECISION MEASUREMENTS |
|
Q1.00062: New Upper Limit on the Electron's Electric Dipole Moment Brendon O'Leary, Jacob Baron, Wesley Campbell, David DeMille, John Doyle, Gerald Gabrielse, Yulia Gurevich, Paul Hess, Nicholas Hutzler, Emil Kirilov, Ivan Kozyryev, Cristian Panda, Maxwell Parsons, Elizabeth Petrik, Benjamin Spaun, Amar Vutha, Adam West We have measured the electron's electric dipole moment (eEDM) to be $d_e = (-2.1 \pm 3.7_{\mathrm{stat}} \pm 2.5_{\mathrm{syst}}) \times 10^{-29} \; e \cdot \mathrm{cm}$.\footnote{The ACME Collaboration et al., \emph{Science} \textbf{343}, (2014) 269--272.}\textsuperscript{,}\footnote{L.~V.~Skripnikov, A.~N.~ Petrov, and A.~V.~Titov, \emph{J.~Chem.~Phys.} \textbf{139}, (2013) 221103.} This corresponds to an upper limit of $|d_e| < 8.7 \times 10^{-29} \; e \cdot \mathrm{cm}$ with 90 percent confidence, which represents an order of magnitude improvement on the previous best limit.\footnote{J.~J.~Hudson, D.~M.~Kara, I.~J.~Smallman, B.~E.~Sauer, M.~R.~Tarbutt, and E.~A.~Hinds, \emph{Nature} \textbf{473}, (2011) 493--496.} We describe our method of measuring the eEDM using a buffer gas cooled beam of thorium monoxide (ThO) and discuss our approach to finding and quantifying systematic effects. [Preview Abstract] |
|
Q1.00063: Search for Electric dipole moment (EDM) in laser cooled and trapped $^{225}$Ra atoms Mukut Kalita, Kevin Bailey, Matthew Dietrich, John Green, Roy Holt, Wolfgang Korsch, Zheng-Tian Lu, Nathan Lemke, Peter Mueller, Tom O'Connor, Richard Parker, Jaideep Singh, Will Trimble We are searching for an EDM of the diamagnetic $^{225}$Ra atom. $^{225}$Ra has nuclear spin I$=$1/2. Experimental sensitivity to its EDM is enhanced due to its heavy mass and the increased Schiff moment of its octupole deformed nucleus. Our experiment involves collecting laser cooled Ra atoms in a magneto-optical trap (MOT), transporting them 1 meter with a far off-resonant optical dipole trap (ODT) and then transferring the atoms to a second standing-wave ODT in our experimental chamber. We will report our recent experiences in polarizing and observing Larmor precession of $^{225}$Ra atoms in parallel electric and magnetic fields in a magnetically shielded region and progress towards a first measurement of the EDM of $^{225}$Ra. [Preview Abstract] |
|
Q1.00064: The hyperfine interaction in $^{171}$YbF Richard Mawhorter, Zachary Glassman, Jens-Uwe Grabow, Anh Le, Timothy Steimle Motivated by recent further improvements in determining the upper limit for the CP-violating electric dipole moment of the electron (eEDM), the pure rotational spectrum of the open shell molecule ytterbium fluoride, $^{171}$YbF, in the $X^{2}\Sigma^{+}$ ($v =$0) state has been recorded using Fourier transform microwave (FTMW) spectroscopy and pump/probe microwave optical double resonance (PPMODR) spectroscopy. The pure rotational spectra and precisely measured splittings in the (0,0) $A^{2}\Pi_{1/2} \leftarrow $ $X^{\, 2}\Sigma^{+}$ band were analyzed to produce an improved set of fine and magnetic hyperfine parameters for the $X^{2}\Sigma^{+}$ ($v =$0) state of $^{171}$YbF. These will be used in conjunction with new FTMW data for $^{170,172,174,176}$YbF in a multi-isotope Dunham U$_{ij}$ fit to provide stable predictions for the rotational spectrum of $^{173}$YbF. Observing the nuclear electric quadrupole hyperfine structure of this isotopologue will help characterize the critical electric field at the heavy atom nucleus. This provides an important benchmark for the molecular wavefunctions used to calculate the effective internal field strength in this and other species, which in turn go into determining the eEDM upper limit. Similar work with the isotopologues of PbF, where nearby states of opposite parity have already been found, will also benefit proposed anapole moment and variation of fundamental constants studies. [Preview Abstract] |
|
Q1.00065: Francium Trapping Facility at TRIUMF for weak interaction studies J. Zhang, L.A. Orozco, R. Collister, G. Gwinner, M. Tandecki, J.A. Behr, M.R. Pearson, E. Gomez, S. Aubin We present the current status of the Francium Trapping Facility at TRIUMF. After successfully commissioning the capture chamber we are now in the process of finishing the science chamber where weak interaction measurements on Fr will be performed. We require transfer of the cold atoms from the capture chamber to the science chamber where they can be re-trapped for precision spectroscopy. The modular design of the science chamber allows for microwave studies for the anapole moment measurement and optical studies for the weak charge measurements using atomic parity non-conservation. We will present our current status and the plans for the commissioning run of the science chamber. [Preview Abstract] |
|
Q1.00066: Parity Violation in Cs and Fr Z. Zuhrianda, Ulyana Safronova, Marianna Safronova 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 experimental work for Fr is in progress at TRIUMF [Sheng et al., J. Phys. B 43, 074004 (2010)]. In this work, we carried out high-precision relativistic all-order calculations of the spin-independent and spin-dependent PNC amplitudes in the $6s-7s$ transition in Cs and the $7s-8s$ transition in Fr using relativistic all-order method in which all single, double, and partial triple excitations of the Dirac-Fock wave functions are included to all orders of perturbation theory. Detailed investigation of the highly-excited state contributions to PNC amplitudes were carried out at the all-order level. These terms were recently demonstrated to give large contribution to the uncertainty of the extracted Cs weak charge $Q_W$ value [V. A. Dzuba et al., Phys. Rev. Lett. 109, 203003 (2012)] and more accurate treatment was needed. The Cs all-order result for the spin-dependent amplitude was found to be consistent with the older atomic physics value of the anapole coupling constant. [Preview Abstract] |
|
Q1.00067: Progress Towards a Compact Optical Clock at JPL Scott Sullivan, Wade Rellergert, Ivan Grudinin, Lukas Baumgartel, Nan Yu The unprecedented stability and accuracy provided by optical clocks allows improved navigation and planetary science in space applications as well as more precise tests of fundamental laws of physics. However, technological advances towards the miniaturization of the physical volume and reduced power consumption of these clocks must be made to suit space-based application. We will describe JPL's effort towards the development of a compact, low-power optical clock based on $^{\mathrm{171}}$Yb$^{\mathrm{+}}$. [Preview Abstract] |
|
Q1.00068: Miniature Microwave Frequency Standard with Trapped $^{171}$Yb$^{+}$ Peter Schwindt, Yuan-Yu Jau, Adrian Casias, Darwin Serkland, Ronald Manginell, Matthew Moorman, John Prestage, Nan Yu, James Kellogg, Dan Boschen, Igor Kosvin We report the development of a low-power, miniature $^{171}$Yb trapped ion clock at Sandia National Laboratories. The ultimate goal of this development effort is to construct a frequency standard that has a frequency stability comparable to a commercial Cs beam standard, but with 100 to 1000 times smaller size and power consumption. The $^{171}$Yb ion has a ground state hyperfine splitting of 12.6 GHz that we use as the ``clock'' transition, and the linewidth of the clock resonance is expected to be less than 10$^{-3}$ Hz, which leads to a very high-Q clock resonance. An atomic clock using trapped ions is an excellent candidate for miniaturization because ions are well isolated from the environment independent of the size of the trap. We have successfully developed miniature ion-trap vacuum packages with sizes ranging from 1 to 10 cubic centimeters. A few microTorr of He buffer gas is introduced into each of our miniature vacuum packages for collisional cooling of the trapped ions. The vacuum packages are sealed and passively pumped by non-evaporable getters. Using a sealed 3 cm$^{3}$ ion-trap vacuum package in combination with miniaturized lasers, optics, and electronics, we constructed a miniature clock prototype that demonstrated excellent long-term stability reaching the 10$^{-14}$ range after a few days of integration. [Preview Abstract] |
|
Q1.00069: Magnetic Dipole and Electric Quadrupole Moments of the $^{229}$Th Nucleus M.S. Safronova, U.I. Safronova, A.G. Radnaev, C.J. Campbell, A. Kuzmich The electromagnetic nuclear moments are fundamental quantities that play an important role in many atomic, nuclear, and solid state processes. While nuclear magnetic moments are known well for many nuclei, many quadrupole moments are known poorly, due to lack of either direct measurements or accurate theoretical values of hyperfine constants $B/Q$ for atomic spectroscopy methods. We report a new method for determining the accuracy of theoretical hyperfine constants $B/Q$ and demonstrate that it can be used to extract the electric quadrupole moment $Q$ with 1-2\% uncertainty for a large number of nuclei. We determine the magnetic dipole $\mu=0.360(7)~\mu_N$ and the electric quadrupole $Q=3.11(6)$~$e$b moments of the $^{229}$Th nucleus by combining our high-precision calculations of the hyperfine constants with measurements reported in C. J. Campbell \textit{et al.}, Phys. Rev. Lett. {\bf 106}, 223001 (2011). We find that the previous value $\mu=0.46(4)$~$\mu_N$ [S. Gerstenkorn \textit{et al.}, J. Phys. 35, 483 (1974)] is incorrect by 25\%. The prospects for further accuracy improvements of $^{229}$Th nuclear moment and possible extraction of the $^{229}$Th$^{3+}$ nuclear magnetic octupole moment are discussed. [Preview Abstract] |
|
Q1.00070: Progress towards a measurement of the proton radius in hydrogen A.C. Vutha, N. Bezginov, I. Ferchichi, M.C. George, M. Weel, C.H. Storry, E.A. Hessels The proton's charge radius continues to have a 7 standard-deviation discrepancy between its CODATA value and determinations from muonic hydrogen measurements. Improved measurements in atomic hydrogen will shed light on this discrepancy. We present a novel experimental scheme, using frequency-offset separated oscillatory fields in standing-wave waveguides, to measure the n=2 Lamb shift in a fast metastable hydrogen beam. We report on our progress, including our first observations of microwave transitions in a fast metastable beam and high signal-to-noise ratio detection in a large-solid-angle photoionization detector. [Preview Abstract] |
|
Q1.00071: Shifts due to quantum-mechanical interference from distant neighboring resonances for saturated fluorescence spectroscopy Alain Marsman, Marko Horbatsch, Eric A. Hessels Quantum-mechanical interference with distant neighboring resonances is found to cause shifts for precision saturated fluorescence spectroscopy of the atomic helium $2 \ {}^3S$-to-$2 \ {}^3P$ transitions. The shifts are significant (larger than the experimental uncertainties for measurements of the intervals) despite the fact that the neighboring resonances are separated from the measured resonances by 1400 and 20 000 natural widths. The shifts depend strongly on experimental parameters such as the angular position of the fluorescence detector and the intensity and size of laser beams. These shifts must be considered for the ongoing program of determining the fine-structure constant from the helium $2 \ {}^3P$ fine structure. The work represents the first study of such interference shifts for saturated fluorescence spectroscopy and follows up on our previous study [1] of similar shifts for laser spectroscopy. \\[4pt] [1] A. Marsman, M. Horbatsch, E.A. Hessels, Physical Review A {\bf 86}, 040501(R) (2012) [Preview Abstract] |
|
Q1.00072: Tunable Laser Frequency Selector for Precision Helium Fine Structure Measurements Nima Hassan Rezaeian, David Shiner Advances in precision in our helium fine structure measurements require a tunable laser frequency selector. Our current electro-optic frequency modulation technique allows for highly flexible, reliable and precise frequency control. However, it does not filter the unused sideband frequencies from the transition inducing laser beam. Recent data and observation indicate that their presence limits improvement in the transition intervals directly, by modifying the count rates, and indirectly, by limiting our ability to stabilize the intensity of the laser sideband that drives the transition. Our goal is to tunably select (t$_{\mathrm{s}}$ \textless 0.1 s) this sideband and remove the unwanted frequencies so we can split the transition linewidths to values approaching 1 part in 10$^{5}$. Our approach uses a narrow band (3 GHz) fiber grating with a fiber based optical circulator to select and isolate the relevant frequency. We have experimented with various techniques to achieve the needed tunability, including both fiber stretching and temperature tuning of a single grating, but favor the following technique. Multiple narrow band gratings in separate fibers are independently temperature stabilized ( $\sim$ 0.01 C) to selectively reflect relevant transition channels, while grating selection via routing is made by a MEMS based fiber switch (t$_{\mathrm{s}} =$ 10 ms). An inline fiber amplifier provides net gain for the implementation. [Preview Abstract] |
|
Q1.00073: High-precision Stark shift measurements using an indium atomic beam Protik Majumder, Nathan Bricault, Benjamin Augenbraun In recent years, we have pursued a series of precise atomic structure measurements in Group III elements--currently thallium and indium--in order to test recent \emph{ab initio} theory calculations in these three-valence-electron systems. We recently completed a precision measurement of the indium scalar polarizability within the 410 nm $5p_{1/2} \rightarrow 6s_{1/2}$ transition using a GaN semiconductor laser interacting transversely with a collimated indium atomic beam in the presence of a large, precisely-calibrated electric field. Our result is in excellent agreement with a new atomic theory calculation. By combining the experimental result and theory expressions, new, precise values for the indium 6p-state lifetimes have been extracted. Currently we are extending this measurement using a second, 1343 nm infrared laser to reach the indium $6p_{1/2}$ state by locking the 410 nm laser and performing two-step spectroscopy. The small infrared absorption in our atomic beam is detected using two-tone FM spectroscopy. The characteristic sideband features in our RF-demodulated spectrum offer built in frequency calibration. For electric fields of order 10 kV/cm, we expect Stark shifts of order 100 MHz for this excited state. [Preview Abstract] |
|
Q1.00074: Precise measurements of $^{203}$Tl and $^{205}$Tl excited state hyperfine splittings and isotope shifts using two-step vapor cell spectroscopy Protik Majumder, Gabrielle Vukasin, David Kealhofer, Gambir Ranjit We have undertaken a series of high-precision atomic structure measurement in thallium to test ongoing \emph{ab initio} atomic structure calculations of relevance to symmetry violation experiments in this element. We have recently completed a two-color, two-step spectroscopy experiment to measure of $7P_{1/2}$ hyperfine structure and isotope shift using a heated thallium vapor cell. One laser, locked to the thallium $6P_{1/2}\rightarrow7S_{1/2}$ 378 nm transition excites both naturally-occurring stable 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 Doppler-free IR absorption spectra of 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 beam provides convenient \emph{in situ} calibration method for the splittings. Our results significantly disagree with older measurements of these intervals. We have currently substituted a new red diode laser system (671 nm) in place of the infrared laser and are studying the thallium 8p$_{1/2}$ state hyperfine structure. [Preview Abstract] |
|
Q1.00075: Precision Measurements of Ba$^+$ Properties Matthew Hoffman, Spencer Williams, Anupriya Jayakumar, E.N. Fortson, Boris Blinov Single trapped barium ions continue to offer a wealth of information about atomic and nuclear structure, oscillator strengths, and polarizabilities. We report progress towards a series of precision measurements that will provide stringent tests of theorists' predictions of these various properties. The first of these is a measurement of the $6S_{1/2} \leftrightarrow 5D_{3/2}$ magnetic dipole transition moment (M1), using a frequency stabilized laser operating at 2051 nm.\footnote{S.R. Williams \emph{et al.}, PRA \textbf{88} 012515 (2013)} This measurement is of interest, as knowledge of M1 is necessary in a proposed measurement of atomic partity nonconservation (PNC).\footnote{E.N. Fortson, PRL \textbf{70} 2383 (1993)} The second is a radio-frequency (rf) spectroscopic measurement of the hyperfine structure of the $5D_{3/2}$, resulting in a measurement of the nuclear magnetic octupole moment of $^{137}$Ba$^+$. Finally, we have begun work on measuring the branching ratio of spontaneous decay from $5D_{5/2}$ to $6S_{1/2}$ and $5D_{3/2}$. The underlying theory and motivation behind these measurements will be presented, as well as experimental upgrades and recent results. [Preview Abstract] |
|
Q1.00076: Absolute Frequency Measurements of the $D_1$ and $D_2$ Transitions in Aatomic Li Donal Sheets, Jose Almaguer, Jacob Baron, Peter Elgee, Michael Rowan, Jason Stalnaker We present preliminary results from our measurements of the $D_1$ and $D_2$ transitions in Li. The data were obtained from a collimated atomic beam excited by light from an extended cavity diode laser. The frequency of the diode laser was stabilized to an optical frequency comb, providing absolute frequency measurement and control of the excitation laser frequency. These measurements will provide a stringent test of atomic structure calculations and yield information about the nuclear structure. We also discuss plans to extend the technique to other high-lying states in lithium. [Preview Abstract] |
|
Q1.00077: Advances in laser spectroscopy of lithium William A. van Wijngaarden, Hang Yang, Bin Jian A number of experiments have precisely measured fine and hyperfine structure splittings as well as isotope shifts for several transitions at optical frequencies for $^{6,7}$Li. These data offer an important test of theoretical techniques developed by two groups to accurately calculate effects due to QED and the finite nuclear size in 2 and 3 electron atoms. The work by multiple groups studying several transitions in both Li$^+$ and neutral Li permits a critical examination of the consistency of separately, the experimental work as well as theory. Combining the measured isotope shifts with the calculated energy shifts passing these consistency tests permits the determination of the relative nuclear charge radius with an uncertainty approaching $1 \times 10^{-18}$ meter which is more than an order of magnitude better than obtained by electron scattering. Prospects for a precision measurement of the fine structure constant are also discussed. [Preview Abstract] |
|
Q1.00078: Precision measurements of excited state atomic lifetimes based on mode-locked femtosecond lasers Jerry Sell, Alina Gearba, Brian Patterson, Randy Knize, Brett DePaola Measurements of excited state atomic lifetimes provide a valuable test of atomic theory, allowing comparisons between empirical and calculated atomic matrix elements. However, as calculations have progressed the most accurate direct lifetime measurements remain at the 0.1-0.2\% precision level, partly due to the nonlinearity and calibration of conventional timing electronics. We will present our progress toward precision excited state lifetime measurements in Rb where the timing is based upon the repetition rate of a mode-locked femtosecond laser. An apparatus consisting of counter-propagating atomic beams is employed, which cross perpendicular to excitation and ionization laser beams. A chopped cw laser provides excitation to the relevant atomic state, while the output of a mode-locked laser is amplified and frequency-doubled to produce ionization pulses. We vary the delay between excitation and ionization by a multiple of the mode-locked laser period, resulting in an extremely accurate time base for future precision measurements. [Preview Abstract] |
|
Q1.00079: INDIVIDUAL QUBIT SYSTEMS |
|
Q1.00080: Digital quantum simulation of Dirac equation with a trapped ion Yangchao Shen, Xiang Zhang, Junhua Zhang, Jorge Casanova, Lucas Lamata, Enrique Solano, Man-Hong Yung, Jingning Zhang, Kihwan KIm Recently there has been growing interest in simulating relativistic effects in controllable physical system [1,2]. We digitally simulate the Dirac equation in 3$+$1 dimensions with a single trapped ion. We map four internal levels of ${ }^{171}\mbox{Yb}^{+}$ ion to the Dirac bispinor. The time evolution of the Dirac equation is implemented by trotter expansion. In the 3$+$1 dimension, we can observe a helicoidal motion of a free Dirac particle which reduces to Zitterbewegung in 1$+$1 dimension. This work was supported in part by the National Basic Research Program of China Grant 2011CBA00300, 2011CBA00301, the National Natural Science Foundation of China Grant 61033001, 61061130540. KK acknowledge the support from the recruitment program of global youth experts.\\[4pt] [1] L. Lamata, et al., Phys. Rev. Lett. 98, 253005 (2007).\\[0pt] [2] R. Gerritsma, et al., Nature 463, 68 (2009). [Preview Abstract] |
|
Q1.00081: Nonlinear Single Spin Spectrum Analayzer Shlomi Kotler, Nitzan Akerman, Yinnon Glickman, Roee Ozeri Qubits are excellent probes of their environment. When operating in the linear regime, they can be used as linear spectrum analyzers of the noise processes surrounding them. These methods fail for strong non-Gaussian noise where the qubit response is no longer linear. Here we solve the problem of nonlinear spectral analysis, required for strongly coupled environments. Our non-perturbative analytic model shows a nonlinear signal dependence on noise power, resulting in a spectral resolution \emph{beyond the Fourier limit} as well as frequency mixing. We developed a noise characterization scheme adapted to this non-linearity. We then applied it using a single trapped $^{88}$Sr$^+$ ion as the a sensitive probe of strong, non-Gaussian, discrete magnetic field noise. With this method, we attained a ten fold improvement over the standard Fourier limit. Finally, we experimentally compared the performance of equidistant vs. Uhrig modulation schemes for spectral analysis. Phys.Rev.Lett. 110, 110503 (2013), Synopsis at http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.110.110503 [Preview Abstract] |
|
Q1.00082: AQuA: A 2D array of Rydberg coupled atomic qubits Kara Maller, Martin Lichtman, Alex Carr, Michal Piotrowicz, Tian Xia, Larry Isenhower, Mark Saffman We are developing a 2D array of optically trapped single atom qubits for quantum computation experiments. We demonstrate stochastic loading of an average of 30 Cs atom qubits in a 49 site array with 3.8 $\mu\rm m$ site to site spacing. Parallel qubit rotations are performed with microwaves and site selective single qubit gates are demonstrated using focused beams of two-frequency Raman light. Single qubit gate fidelity is characterized with randomized benchmarking. Using Rydberg excitation and blockade we demonstrate conditional phase shifts of pairs of trapped atoms and will report on progress towards running quantum algorithms in the array. [Preview Abstract] |
|
Q1.00083: Techniques to Improve Magnetometry Using NV Centers in Diamond David Le Sage, Chinmay Belthangady, Linh Pham, David Glenn, Ronald Walsworth Nitrogen-vacancy (NV) color centers in diamond can be used to optically measure magnetic fields with nanoscale spatial resolution and excellent sensitivity. We will report on ongoing progress to improve the sensitivity and bandwidth of such NV-diamond magnetometers. Significant improvements to NV spin coherence properties have been made by controlling interactions between NV centers and other spins in the diamond, and techniques have been implemented to increase the fraction of NV fluorescence detected. We will present the latest results from an optimized magnetometer employing a large ensemble of NV centers, and discuss some potential applications of this emerging technology. [Preview Abstract] |
|
Q1.00084: Probing Magnetic Noise near a Conducting Surface with a Single Spin Qubit Arthur Safira, Shimon Kolkowitz, David Patterson, Quirin Unterreithmeier, Alexander Zibrov, Vladimir Manucharyan, Mikhail Lukin Noise emanating from conductors and their surfaces can limit the coherence times and relaxation rates of many promising quantum information systems, from gate-defined quantum dots to atoms and ions on chips. Here we present experimental results of the use of nitrogen vacancy centers (NVs), single electronic spin qubits in diamond, to probe the spectral, spatial, and temperature dependent properties of magnetic noise near conductors. We measure the impact of the magnetic noise on the relaxation rate of NVs implanted at shallow depths over a wide range of temperatures, from 300 K to 7 K, and over an order of magnitude of distances to the conductor, from 200 nm down to 20 nm, a length scale not yet achievable with atoms or SQUIDS. [Preview Abstract] |
|
Q1.00085: Phonon-Induced Coupling and Intersystem Crossing in Nitrogen-Vacancy Centers Michael Goldman, Alp Sipahigil, Steven Bennett, Alexander Kubanek, Mikhail Lukin Nitrogen-vacancy (NV) centers in diamond have emerged as a versatile atom-like system, finding applications in both metrology and quantum information science. In both regimes, it is crucial to understand the interactions between the NV center's electronic state and vibrations in the diamond lattice. The NV center's broad appeal as a sensor -- for nano-scale, bio-compatible thermometry and magnetometry, for example -- hinges on our ability to initialize and read out the electronic state with a single non-resonant laser. Both of these mechanisms are the result of an inter-system crossing (ISC) into a metastable state, a phonon-assisted shelving process that has not been fully explained. Conversely, the NV center's appeal as a precisely controllable quantum register depends on our ability to resonantly excite either closed cycling transitions or closed lambda transitions. The fidelity of operations that depend on these transitions can be degraded by phonon-induced mixing of electronic orbital states within the excited state manifold, which can provide an unwanted non-radiative decay channel out of the desired subspace. We have directly measured population dynamics and decoherence in the excited state manifold. We have quantified the phonon-induced mixing rate and demonstrated that mixing can be completely suppressed at low temperatures. Further, we have measured the ISC rate for different excited states and developed a theoretical model that unifies the phonon-induced mixing and ISC mechanisms. [Preview Abstract] |
|
Q1.00086: Quantum optics in the solid state with diamond nanophotonics Ruffin Evans, Nathalie de Leon, Kristiaan De Greve, Yiwen Chu, Brendan Shields, Birgit Hausmann, Michael Burek, Patrick Maletinsky, Alexander Zibrov, Hongkun Park, Marko Loncar, Mikhail Lukin Quantum networks require interfaces between photons and quantum bits. Nitrogen vacancy (NV) centers in diamond are a promising candidate for this interface: they are optically addressable, have spin degrees of freedom with long coherence times, and can be easily integrated into solid-state nanophotonic devices. The crucial optical feature of the NV is its zero-phonon line (ZPL), a cycling transition allowing coherent optical manipulation and read-out of the spin. However, the ZPL only accounts for 3-5\% of the NV emission, and previous methods of producing NV centers yield unstable ZPLs. I will present methods for controlling NV emission by coupling NV centers to nanophotonic devices. In particular, we create a high-density layer of NVs with stable ZPLs in high purity diamond; carve waveguides out of the diamond substrate; and fabricate high quality factor, small mode volume photonic crystal cavities around NVs in these waveguides. We observe an enhancement of the NV emission at the cavity resonance by a factor of 100. These devices will become building blocks for quantum information processing such as single photon transistors, enabling distribution of entanglement over quantum networks. [Preview Abstract] |
|
Q1.00087: A Nanophotonic Quantum Phase Switch with a Single Atom Jeff Thompson, Tobias Tiecke, Thibault Peyronel, Nathalie de Leon, Lee Liu, Kali Nayak, Vladan Vuletic, Mikhail Lukin In analogy to transistors in classical electronic circuits, quantum optical switches are the fundamental building blocks of quantum networks. They are important for many applications including quantum repeaters for long-range quantum communication, distributed quantum information processing and simulating quantum states of matter. We present recent experimental results on a scalable quantum optical switch consisting of a single atom trapped near a nanoscale photonic crystal cavity [1]. First, we show that the spin state of the atom controls the propagation of light through the switch, imposing a state-dependent optical phase shift of $\pi$. Second, we show that a single photon incident on the switch can coherently change the state of the atom, allowing the switch to be gated from ``on" to ``off'' with only a single quantum of input. Lastly, we demonstrate the truly quantum nature of the switch by showing that it acts differently on single photon inputs compared to photon pairs. These results and techniques pave the way towards large-scale integrated quantum nanophotonic networks involving multiple atoms situated near complex optical circuits. \\[4pt] [1] Thompson, J. D., Tiecke, T. G., \textit{et. al.}, ``Coupling a Single Trapped Atom to a Nanoscale Optical Cavity.'' Science, 340, 1202--1205 (2013). [Preview Abstract] |
|
Q1.00088: Towards nondestructive state detection of SiO$^+$ Huanqian Loh, Shiqian Ding, Roland Hablutzel, Dzmitry Matsukevich Molecular ions, with their long coherence times and rich internal structure, are suitable candidates for precision measurement studies such as the variation of fundamental constants. Detecting the state of molecular ions, however, tends to invoke destructive methods such as resonance-enhance multi-photon dissociation (REMPD). In contrast, photon recoil spectroscopy and quantum logic spectroscopy are two techniques that offer nondestructive state detection. Both techniques involve mapping the internal state of the spectroscopy ion onto the motional state of an auxiliary ion that can then be detected using Raman lasers. We report on our application of both techniques on two co-trapped Yb$^+$ ions of different isotopes. We also discuss our general progress towards implementing them on the SiO$^+$ molecular ion. [Preview Abstract] |
|
Q1.00089: Low Temperature Symmetric Dynamical Decoupling in NV Centers Linh Pham, Dima Farfurnik, Andrey Jarmola, Dmitry Budker, Nir Bar-Gill, Ronald Walsworth Over the past few years nitrogen-vacancy (NV) centers in diamond have emerged as a leading platform for quantum information processing and sensing. Dynamical decoupling schemes have been used to extend the coherence time of NVs up to nearly 1 second at cryogenic temperatures. However, thus far most research focused on single axis decoupling (namely CPMG sequences), which are not as useful for practical applications. Here we extend previous work, studying the coherence times achievable using symmetric decoupling sequences (namely the XY family), both at room temperature and at low temperatures. We analyze the effects of pulse errors, which become significant in this regime, and address potential applications, such as enhanced magnetometry, quantum memory, and interaction-dominated dynamics. [Preview Abstract] |
|
Q1.00090: Resonant Coupling Between NV Centers and Dark Spins at the Surface of Diamond Linh Pham, Chinmay Belthangady, Stephen DeVience, Nir Bar-Gill, Junghyun Lee, Paola Cappellaro, Mikhail Lukin, Amir Yacoby, Ronald Walsworth Recent studies of the surface of diamond have revealed the presence of as-yet-unidentified dark electronic spins on the diamond-air interface. These spins could serve as very sensitive probes of their local magnetic field environment. Of particular interest is the possibility of enhancing sensitivity in diamond-based nano-scale nuclear magnetic resonance (NMR) experiments due to the close proximity of nuclear spins to these dark surface spins. An efficient route towards initialization and spin-state detection of the dark spins is provided by controlled coupling with nitrogen-vacancy (NV) color centers, which can be spin polarized and readout optically. We describe the use of dressed-state schemes to achieve such resonant coupling, which may enable NMR spectroscopy and imaging of individual nuclear spins in samples on the diamond surface. [Preview Abstract] |
|
Q1.00091: Toward Remote Entanglement with $^{138}$Ba$^{+}$ Carolyn Auchter, Thomas W. Noel, Chen Kuan Chou, Boris B. Blinov We present work toward remote ion entanglement using systems of singly trapped $^{138}$Ba$^{+}$ ions. Remote ion entanglement will be achieved through photon mediated entanglement swapping using spontaneously emitted 493 nm photons\footnote{C. Simon and W. T. M. Irvine, Phys. Rev. Lett. \textbf{91}, 110405 (2003)}. This scheme is an excellent candidate for a ``loophole-free'' Bell Inequality test due to the low decoherence and capability for fast control and detection of the $^{138}$Ba$^{+}$ qubit and the suitability of the relatively long wavelength of the emitted photons for fiber optic transmission. In order to improve the future rate of remote ion entanglement generation, we present work on employing ultrafast pulses from a mode-locked Ti:Sapphire laser to increase the rate of ion-photon entanglement and improve fidelity. Progress toward ion-ion entanglement of ions in adjacent traps will be reported. [Preview Abstract] |
|
Q1.00092: Ion-photon entanglement with trapped Ba-138 ions Thomas Noel, Carolyn Auchter, Chen-Kuan Chou, Boris B. Blinov We demonstrate entanglement between the polarization state of spontaneously emitted photons and the Zeeman state of a single trapped Barium ion. The Barium ion is weakly excited with a short ($\sim$20 ns) pulse of CW laser light. The ion subsequently decays emitting a single photon at 493 nm. Entanglement is verified by measuring the states of the ion and photon in multiple bases, yielding an overlap of 0.84 with the appropriate maximally entangled Bell state. Furthermore, the CHSH form of the Bell inequality is shown to be violated by over eight standard deviations. This work demonstrates elements of an apparatus which will make our long-term goal of achieving a loophole-free test of a Bell inequality possible. [Preview Abstract] |
|
Q1.00093: Quantum control and simulation with 2-dimensional arrays of trapped ions J.W. Britton, B.C. Sawyer, J.G. Bohnet, J.J. Bollinger, A.C. Keith, D. Meiser Trapped ions, when cooled to sufficiently low temperatures form crystalline arrays. We describe our efforts to extend the quantum control techniques developed with small linear chains of ions in rf traps to larger two-dimensional crystals of hundreds of ions formed in a Penning trap. Our qubit is the 124 GHz electron spin-flip transition in the ground state of Be$^{+}$ in the 4.5 T magnetic field of the Penning trap. We control the spins with an effective transverse magnetic field generated with 124 GHz microwaves. Spin-dependent optical dipole forces (ODF) are used to engineer long range Ising interactions between the ion qubits and to characterize the motional degrees of freedom of the trapped ions. We will discuss the design and implementation of a new Penning trap that employs an m=3 rotating wall and enables the application of an ODF with lower spontaneous emission. We will also discuss simulation work that provides information on the temperature of the in-plane modes. [Preview Abstract] |
|
Q1.00094: Progress Towards a Multispecies Ion System for Remote and Local Entanglement Generation Grahame Vittorini, Ismail Inlek, David Hucul, Clayton Crocker, Christopher Monroe Entanglement within and across remote trapped ion quantum registers has been previously demonstrated with $^{171}$Yb$^+$. In order to generate remote entanglement, a pulsed laser excites an ion in each register and the spontaneously emitted photons are collected. However, there is a similar probability that uncollected photons will scatter from adjacent ions, resulting in the loss of locally stored quantum information. To address this issue, we are implementing a multispecies system in which Yb$^+$ acts as a quantum memory and Ba$^+$ provides a photonic interlink. Not only does this minimize disruption of the Yb$^+$ quantum memory qubits, but photons from both the 493 nm and 650 nm transition in Ba$^+$ are more easily converted to telecom wavelengths. We report progress on such a system which requires co-trapping of these species, quantum logic spectroscopy for state detection, and the implementation of a multi-species phase gate utilizing a single pulsed laser. [Preview Abstract] |
|
Q1.00095: Diabatic spectroscopy with cold ion quantum simulation Bryce Yoshimura, Wes Campbell, James Freericks An experimental simulation that adiabatically prepares a nontrivial ground state of trapped ions becomes more and more difficult as the number of ions increase. The difficulty of the adiabatic preparation is due to the decoherence time and the minimum energy gap, that shrinks as the number of ions increase. We propose a spectroscopy protocol that takes advantage of the diabatic effect by intentionally populating the excited states and then performing Fourier analysis to extract the energies of the low-lying excited states. We explore the diabatic spectroscopy protocol by simulating the transverse-field Ising model, where one can perform analysis on large systems when the interactions do not decay with distance. To simulate experimental data, noise from counting statistics and decoherence error is added to the resulting signal from the simulations. By using a signal processing technique known as compressive sensing we can sharply reduce the amount of data needed to extract the energy spectrum. [Preview Abstract] |
|
Q1.00096: Ultrafast entanglement of trapped ions Brian Neyenhuis, Kale Johnson, Jonathan Mizrahi, David Wong-Campos, Christopher Monroe We have demonstrated ultrafast spin-motion entanglement of a single atomic ion using a short train of intense laser pulses. This pulse train gives the ion a spin-dependent kick where each spin state receives a discrete momentum kick in opposite directions. Using a series of these spin-dependent kicks we can realize a two qubit gate. In contrast to gates using spectroscopically resolved motional sidebands, these gates may be performed faster than the trap oscillation period, making them potentially less sensitive to noise. Additionally this gate is temperature insensitive and does not require the ions to be cooled to the Lamb-Dicke limit. We show that multiple kicks can be strung together to create a ``Schrodinger cat'' like state, where the large separation between the two parts of the wavepacket allow us to accumulate the phase shift necessary for a gate in a shorter amount of time. We will present a realistic pulse scheme for a two ion gate, and our progress towards its realization. [Preview Abstract] |
|
Q1.00097: Highly Flexible Home-built ND:YVO4 Modelocked Laser System for Trapped Ion Qubit Raman Transitions Tomasz Sakrejda, John Wright, Richard Graham, Zichao Zhou, Boris Blinov A passively mode-locked ND:YVO4 laser system for driving Raman transitions in Ba+ and Yb+ is constructed and evaluated. Based on on a commercial CW laser platform, we make straightforward modifications to the cavity to effect passive mode locking. With 20W of 808nm diode pump light, we achieve over 4 W 1064 nm output power, 150 MHz repetition rate, and 17 ps pulse duration. Laser cavity parameters can be easily modified to facilitate changes in pulse duration or repetition rate. Stable mode locking is achieved at start-up with no perturbations to the cavity resonator. The output 1064nm light can frequency-doubled in an external LBO crystal to generate up to 130 mW of 532 nm light in a single pass. The 532 nm light is close enough to the 493 nm line in Ba+ to drive ground state qubit flips with a single laser pulse. We plan to use this laser to drive qubit gates in both Ba 138+ and, with a third harmonic (355 nm) generation system, in 171Yb+. [Preview Abstract] |
(Author Not Attending)
|
Q1.00098: The experimental study on Fock states thermalization in a trapped ion system Yao Lu, Shuoming An, Mark Um, Dingshun Lv, Kihwan Kim We report on the experimental study about the thermalization process of phonon number Fock states in a trapped ion system. Heating in the system disturbs a prepared motional quantum state and leads to a thermal distribution. It is believed that heating is caused by electric field fluctuation from the trap electrodes. In experiment, we prepare a Fock State n and wait for a certain amount of time, then measure the phonon distribution by applying the standard red and blue sideband transition and analyzing the interference pattern from different frequencies of Rabi oscillation depending on motional quantum number. The measured heating dynamics is well described by master equation, where a single atom is coupled to a thermal reservoir. This work was supported in part by the National Basic Research Program of China Grant 2011CBA00300, 2011CBA00301, 2011CBA00302, the National Natural Science Foundation of China Grant 61073174, 61033001, 61361136003. KK acknowledges the support from the Thousand Young Talents program. [Preview Abstract] |
|
Q1.00099: Addition and subtraction of single phonons in a trapped ion system Dingshun Lv, Shuoming An, Mark Um, Yao Lu, Jingning Zhang, Kihwan Kim We introduce an addition and subtraction of single phonons in a trapped ion system. The creation $\hat{a}^{\dagger}$ and annihilation $\hat{a}$ operation have been realized with photons and used for the complete engineering of quantum states of light and the probe of fundamental quantum phenomena [1]. The mathematical description of photon is identical to that of phonon. However, phonon is a particle of quantized matter wave, which should be interpreted differently from photon. We implement the addition and the subtraction of phonon by applying an anti-Jaynes-Cummings type of operation on our trapped ion and performing projective measurements. Our realization can be used for the accurate measurement of position and momentum as well as their relation.\\[4pt] [1] V. Parigi, et al., Science 317, 1890 (2007). [Preview Abstract] |
|
Q1.00100: Towards a Quantum Interface between Diamond Spin Qubits and Phonons in an Optical Trap Peng Ji, M. Ummal Momeen, Jen-Feng Hsu, Brian D'Urso, Gurudev Dutt We introduce a method to optically levitate a pre-selected nanodiamond crystal in air or vacuum. The nanodiamond containing nitrogen-vacancy (NV) centers is suspended on a monolayer of graphene transferred onto a patterned substrate. Laser light is focused onto the sample, using a home-built confocal microscope with a high numerical aperture (NA $=$ 0.9) objective, simultaneously burning the graphene and creating a 3D optical trap that captures the falling nano-diamond at the beam waist. The trapped diamond is an ultra-high-Q mechanical oscillator, allowing us to engineer strong linear and quadratic coupling between the spin of the NV center and the phonon mode. The system could result in an ideal quantum interface between a spin qubit and vibrational phonon mode, potentially enabling applications in quantum information processing and sensing the development of quantum information storage and processing. [Preview Abstract] |
|
Q1.00101: Progress Towards Quantum Simulation Using Micro-fabricated Ion Traps K. Wright, C. Cao, G. Ji, T. Brennan, C. Monroe We report our current experimental progress towards using surface electrode traps for quantum simulation. Current progress is being made using a micro-fabricated Satellite trap from GTRI. This trap features two long storage arms which can be used to hold ions in reserve to mitigate the need to load ions via a heated oven in the event of ion loss. This should allow trapping of long ion chains with a substantial decrease in the time needed to recover an ion chain of a given length. The trap has 96 electrodes for fine control of the DC potential needed to create large anharmonic trapping wells. It also features two crossing linear regions for the ordering of mixed ion chains by selective shuttling between the arms of intersecting linear regions of the trap. This should allow us to trap multiple species and explore the advantages of having sympathetic coolant ions. Interspersing these ions through a chain of ions undergoing coherent operations potentially could increase the chain lifetime as well as mitigate certain heating effects. We hope to use these features as the next step in increasing the size of current quantum simulations being done at UMD, which are aimed at exploring quantum phenomena in spin systems. [Preview Abstract] |
|
Q1.00102: QUANTUM OPTICS |
|
Q1.00103: Electron Steering with a Low-Power Optical Laser Peter Beierle, Wayne Huang, Roger Bach, Maria Becker, Derek Ruffner, Herman Batelaan As a beam of 4 keV electrons pass by a metallic wall which is illuminated by a laser beam (typically 10 mWatt and 658 nm), the electrons experience a force that deflects the beam's direction by 550 $\mu rad$ when the electrons are approx. 10 $\mu m$ from the surface [1]. This ``electron switch'' has a response time of approximately 6 $\mu s$; the deflection of the electron beam is shown to decrease as the beam's distance to the wall increases beyond the laser spot size, giving an observed electron deflection up to 200 $\mu m$ from the surface.This switching mechanism is shown to be robust, as it is demonstrated for various optical wavelengths and surfaces. This type of electronic-free electron manipulation has potential use in electron beam microscopy (EBM) and electron beam lithography (EBL). In addition, while diffracting a 10keV electron beam through a nanofabricated electron grating, we observe the effects of illuminating the grating with a laser beam, with inconclusive results which seem to depend on the wavelength of the laser and relative angles between the grating and the laser beam {\&} electron beam. \\[4pt] [1] W. Huang, R. Bach, P. Beierle, H. Batelaan,J. Phys. D, ``A Low-Power Optical Electron Switch'' (accepted, forthcoming in February 2014) [Preview Abstract] |
|
Q1.00104: Stochastic nature induced by laser noise in narrow transitions Yuan Sun, Chen Zhang We use a probability-theory approach to study the laser noise's effects on laser-atom interactions. We consider the case where the atom is described by a two-level system without spontaneous emission and the laser has both intensity and frequency noises. A stochastic differential equation is established based on the Schr\"odinger equation of the laser-atom interaction in the semiclassical picture. We then analyze the equation using the path-integral technique to the first order of a perturbation approach. Because of the presence of laser noises, the atom wave function at a given time is a random variable. Therefore we construct a stochastic process charactering its time evolution. We also provide the theoretical description for the experimental realization of measuring the laser line width by driving a narrow atomic transition, and establish the connection between the laser noise's roles in the laser-atom interaction and laser line width measurement by beat signal. [Preview Abstract] |
|
Q1.00105: Efficient blue light generation using periodically poled stoichiometric lithium tantalate via resonant frequency doubling Ali Khademian, Shilpa Jadhav, David Shiner Convenient high power blue diode lasers with single frequency operation are still under developments and are not as well developed and cost effective as IR laser sources. Harmonic generation of IR lasers provide a viable alternative source of blue and UV light. Magnesium oxide doped periodically poled Stoichiometric Lithium Tantalate (PPMgO:SLT) has been reported to have the lowest blue, IR and blue induced IR absorption (BLIIRA) among ferroelectric crystals such as Lithium Niobate (PPLN) and Potassium Titanyl Phosphate (PPKTP). All these properties, along with higher thermal conductivity, make this crystal an excellent candidate for efficient blue light generation using second harmonic generation (SHG) in a resonant buildup cavity. Efficient resonant doubling is very sensitive to various cavity and crystal loss mechanisms. Recently we obtained 400 mW of blue light at 486 nm with net conversion efficiency of 77{\%} using a 515 mW fiber grating stabilized IR source. Sources of conversion loss have been identified and evaluated with various methods in our investigation. These include reflection, scattering, absorption, and polarization rotation of IR light in the crystal, as well as mode mismatching and spherical aberration due to focusing lenses. The locking and electronic control functions of the cavity are automated using an internally mounted single chip microcontroller with embedded DSP (digital signal processor). [Preview Abstract] |
|
Q1.00106: Parametric Four-Wave Mixing Using a Single cw Laser Erik Brekke, Emily Herman, Laura Alderson We present progress in using parametric four-wave mixing in a rubidium cell for the generation of coherent emission at 420 nm and 5.4 $\mu $m. A simple system using a single external cavity diode laser at 778 nm and a tapered amplifier supplies the needed optical beams. The efficiency is limited by absorption of the 420 nm beam, with single pass outputs of 40 $\mu $W. Optical pumping presents a possibility for increased output powers, but radiation trapping must be overcome at high densities. Several methods for increasing the effectiveness of the process are currently underway. The resulting beam at 420 nm presents an intriguing alternative method of exciting Rydberg states in Rubidium atoms. [Preview Abstract] |
|
Q1.00107: Continuous time quantum random walks in free space Toni Eichelkraut, Christian Vetter, Armando Perez-Leija, Demetrios Christodoulides, Alexander Szameit We show theoretically and experimentally that two-dimensional continuous time coherent random walks are possible in free space, that is, in the absence of any external potential, by properly tailoring the associated initial wave function. These effects are experimentally demonstrated using classical paraxial light. Evidently, the usage of classical beams to explore the dynamics of point-like quantum particles is possible since both phenomena are mathematically equivalent. This in turn makes our approach suitable for the realization of random walks using different quantum particles, including electrons and photons. To study the spatial evolution of a wavefunction theoretically, we consider the one-dimensional paraxial wave equation $(i\partial_{z}+\frac{1}{2k}\partial^2_{x})\Psi=0$. Starting with the initially localized wavefunction $\Psi(x,0)=exp[-x^2/2\sigma^2]J_0(\alpha x)$, one can show that the evolution of such Gaussian-apodized Bessel envelopes within a region of validity resembles the probability pattern of a quantum walker traversing a uniform lattice. In order to generate the desired input-field in our experimental setting we shape the amplitude and phase of a collimated light beam originating from a classical HeNe-Laser (633 nm) utilizing a spatial light modulator. [Preview Abstract] |
|
Q1.00108: ABSTRACT WITHDRAWN |
|
Q1.00109: Self-Stabilizing Measurement of Phase Sai Vinjanampathy Measuring phase accurately constitutes one of the most important task in precision measurement science. Such measurements can be deployed to measure everything from fundamental constants to measuring detuning and tunneling rates of atoms more precisely. Quantum mechanics enhances the ultimate bounds on the precision of such measurements possible, and exploit coherence and entanglement to reduce the phase uncertainty. In this work, we will describe a method to stabilize a decohering two-level atom and use the stabilizing measurements to learn the unknown phase acquired by the atom. Such measurements will employ a Bayesian learner to do active feedback control on the atom. We will discuss some ultimate bounds employed in precision metrology and an experimental proposal for the implementation of this scheme. [Preview Abstract] |
|
Q1.00110: Controlling Quantum Chaos Bibek Pokharel, Arjendu Pattanayak We have recently computed Lyapunov exponents describing the chaotic behavior of the quantum trajectories of an open quantum nonlinear oscillator using the Quantum State Diffusion formalism. We have seen several interesting features as a function of changing system parameters. We report on progress towards controlling the observed quantum chaotic behavior using the classical Ott-Grebogi-Yorke protocol. [Preview Abstract] |
|
Q1.00111: Worldline Method for Electromagnetic Casimir Energies Jonathan Mackrory, Tanmoy Bhattacharya, Daniel Steck We present our work on the worldline method for calculating electromagnetic Casimir energies. The worldline method calculates the energy by generating an ensemble of closed space-time paths via a Monte-Carlo algorithm, and then summing up the contributions from the potential along each path. We calculate the Casimir energy due to dispersionless, dielectric bodies. We decompose the electromagnetic field into two polarizations, which behave as scalar fields. We will present our analytical and numerical work showing agreement for both Casimir-Polder and Casimir energies for atoms and planar dielectric bodies. We will also present results showing the numerical convergence of the algorithm. [Preview Abstract] |
|
Q1.00112: FUNDAMENTAL ISSUES |
|
Q1.00113: A New View of Relativity and its Consequences for the Dirac Equation Felix T. Smith In 1907 and 1908 Minkowski established the foundations of the 4-dimensional tensor description of the electromagnetic field and the associated relativistic geometry with its metric sum $ds^2=dx_1^2+ dx_2^2+ dx_3^2-c^2dt^2$. Knowing no physical source for the time-dependent term he introduced the drastic postulate that time itself constituted a fourth component $x_4=ict$ in a new space-time geometry. This was rapidly accepted (but not by Poincar\'e) and is responsible for the partial disconnect that later developed between relativity and other domains of modern physics. It has never been reappraised in the light of the Hubble expansion of our cosmos. A new alternative relativistic geometry can now be envisaged. In it the term $-c^2dt^2$ corrects for the change with time of a radius of curvature (imaginary because the curvature is negative), $r_{curv}=ic(\tau_{Hubble}+\delta t)$, where $\tau_{Hubble}$ is evaluated at the zero of $\delta t$, so that $dr_{curv}=icdt$. The geometry represents an expanding, negatively curved 3-space, not a 4-dimensional space-time. Relativistic space and time are much more like their prerelativistic counterparts. Important consequences for the Dirac equation will be presented. [Preview Abstract] |
|
Q1.00114: Schrodinger Equation Domain Structure Variations Bruce Toy Schr\"{o}dinger's Equation can be used to represent the total energy of particles and waves. With the appropriate selection of time domain, spatial domain, and field conditions it is possible to give a new definition to the transitions and interactions between particle and wave representations. Mass is treated as a spatial domain solution to the wave equation and energy as a time domain solution. The results offer a better understanding of wave-particle processes. [Preview Abstract] |
|
Q1.00115: The nature of magnetic phenomena is the electric phenomenon new interpretation Yongquan Han The nature of magnetic phenomena is the electric phenomenon, that is the result of the negative and positive charge of the regular ``matrix,'' also a positive, negative charge spread by the form of the ``matrix,'' but also can be said to be the waves of electric current (the current spread by the form of wave but only transfer form, the form is not move with wave), its characteristics are: magnetic field plane and the current plane is perpendicular to each other (make up the current wave), inside the material, it performance the current wave (electric field \textless - \textgreater , magnetic field). Sent to outer space it become an electromagnetic wave, an electromagnetic wave particle (positive, negative particle move in a circle)is the smallest needle, it is unified with Maxwell electromagnetic theory, magnetic monopoles do not exist. The mechanism of information between cable transmission and wireless transmission is the same. [Preview Abstract] |
|
Q1.00116: Boundary Condtions of Gravity Shantilal Goradia Our quantum mechanical derivation of the strong coupling using modified Newtonian inverse square logic in (1) and the fine structure constant (ALPHA) using Boltzmann expression in our book (2) come close to Einstein (1919) merging nuclear force with gravitation and retracting his cosmological constant. Its conflict with the inflationary aspect of the universe can be reconciled with the possibility that the light coming from the receding galaxies follow a curvilinear path increasing in length due to its ever increasing curvature without receding only in the radial direction. In (1), we implicitly show gravity as nothing but the cumulative effect of quantum mechanical forces, making G vary at different locations in the universe. The subsequent effects of gravitational variation would be on the curvature of the paths of the geodesics they create. Further investigation along these lines is warranted as we do not have unification, evidence of graviton, quantum gravity or anything else very concrete after a century of hard work. Strong coupling and ALPHA may be the boundary conditions of gravitational constants. Newtonian Gravity in Natural Units, Journal of Physical Science and Application 2 (7) (2012)265-268, [2] Quantum Consciousness - The Road to Reality by S. Goradia, 4/27/20 [Preview Abstract] |
|
Q1.00117: PHOTON INTERACTIONS WITH ATOMS, IONS AND MOLECULES |
|
Q1.00118: Pump-Probe spectroscopy with a femtosecond monochromatic VUV light source Wei Cao, Itzik Ben-Itzhak, Charles Lewis Cocke A table-top pump-probe set-up combining our Vacuum Ultra-Violet (VUV) monochrometor and cold target recoil-ion momentum spectroscopy (COLTRIMS) apparatus has been developed. High flux VUV photons are generated from a semi-infinite gas cell via high order harmonic generation. A dispersion-compensated grating pair is used to select a single harmonic with pulse duration below a 100 femtosecond. The VUV photon energy is tunable from 10 to 20 eV with a bandwidth of less than 200 meV. Such a VUV source can strongly interact with valence electrons of most molecules, thus trigger chemical reactions with well-defined time-energy information. A following synchronous infrared pulse is applied to probe or control the process. The reaction products are momentum-imaged in coincidence by the COLTRIMS system, thus enabling channel-resolved measurements. A few proof-of-principal experiments on the simplest molecular system, D$_{\mathrm{2}}$, are demonstrated. [Preview Abstract] |
|
Q1.00119: Channel competition in strong-field dissociation of a CS$^{+}$ target Bethany Jochim, K.J. Betsch, M. Zohrabi, U. Ablikim, T. Severt, Ben Berry, A.M. Summers, K.D. Carnes, I. Ben-Itzhak Using a coincidence 3-D momentum imaging technique, we study ultrafast laser-induced dissociation of a CS$^{+}$ ion beam. Over a wide laser intensity range, from 10$^{10}$ to 10$^{16}$ W/cm$^{2}$, we find clear alternation in the dominance of the C$^{+}+$ S and C $+$ S$^{+}$ channels with intensity. Moreover, low-kinetic energy release (KER) ($\le $1 eV) dissociation in both channels at the lower end of the intensity range suggests the intriguing possibility of photodissociating metastable states being involved. Utilizing an estimate of the initial vibrational population, measured KER and angular distribution spectra, and the molecular ion's calculated electronic structure, we examine the dynamics underlying the observed intensity-dependent channel competition. [Preview Abstract] |
|
Q1.00120: Three-body fragmentation of triatomic molecular ions in a strong laser field U. Ablikim, M. Zohrabi, Bethany Jochim, Ben Berry, K.D. Carnes, I. Ben-Itzhak Coincidence three-dimensional momentum imaging measurements of three-body fragmentation of transient triply-charged CO$_2$ molecules reveal competing fragmentation paths involving bending, symmetric and asymmetric stretching, as well as the more complex sequential breakup (i.e. one bond at a time) [1,2]. We have extended these studies using a CO$_2^+$ molecular-ion-beam target, providing similar results for the breakup of the transient CO$_2^{3+} \rightarrow$ O$^++$C$^++$O$^+$. The detection of neutral fragments also enables kinematically complete measurements of the three-body breakup of the transient CO$_2^{2+}$. Our results, for CO$_2^+$ in ultrashort ($\sim$26 fs) intense (10$^{15}$ to 10$^{16}$ W/cm$^2$) laser pulses at 790 nm, suggest significant bending in the C$^++$O$^++$O$^+$ channel as well as sequential breakup. In contrast, sequential breakup is suppressed in the O$^++$C$^++$O and O$^++$C$+$O$^+$ channels.\\[4pt] [1] N. Neumann \textit{et al.}, Phys Rev. Lett. \textbf{104}, 103201 (2010)\\[0pt] [2] Cong Wu \textit{et al.}, Phys Rev. Lett. \textbf{110}, 103601 (2013) [Preview Abstract] |
|
Q1.00121: Fragmentation pathways of ethylene after core ionization B. Gaire, I. Bocharova, F.P. Sturm, N. Gehrken, D. J. Haxton, A. Belkacem, Th. Weber, M. Zohrabi, I. Ben-Itzhak, A. Gatton, J. Williams, D. Reedy, C. Nook, A. Landers, H. Gassert, S. Zeller, J. Voigtsberger, T. Jahnke, R. Doerner We have measured the Auger electrons in coincidence with the recoil ions, resulting from the core ionization of ethylene molecules, by employing the COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS) method. The Auger-electron and recoil-ion energy maps are used to identify the fragmentation pathways and they are compared to the valence photo-double-ionization of ethylene. The dicationic electronic states favored by the propensity rules are identified and their role on the fragmentation pathways is discussed. The molecular-frame Auger electron angular distribution provides further insight into the breakup of this molecule after core ionization. [Preview Abstract] |
|
Q1.00122: Carrier-envelope phase effects in state-selective measurements of D* fragments from D$_2$ molecules Ben Berry, M. Zohrabi, U. Ablikim, Nora G. Kling, Travis Severt, Bethany Jochim, K. D. Carnes, B. D. Esry, I. Ben-Itzhak The yield of long-lived D* fragments from D$_2$ in intense, few-cycle laser pulses exhibits a strong carrier-envelope phase (CEP) dependence. Similar CEP effects are observed in the spatial asymmetry, defined as the normalized yield difference between events in each direction along the laser polarization. By field ionizing highly excited D* fragments we are able to limit the range of excited states measured. This allows for CEP control studies of small subsets of D* states, i.e. Rydberg D($nl$) with $n$ on the order of 25-50. Furthermore, we Fourier transform the CEP-dependent observables to gain insight into the photon pathways involved in the D* formation. This strategy is supported by a theoretical framework that links CEP effects to interferences between pathways involving different numbers of photons [1, 2].\\[4pt] This work was supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, Grant No. DE-FG02-86ER1349. The PULSAR laser was provided by Grant No. DE-FG02-09ER16115 from the same funding agency. \\[4pt] [1] V. Roudnev and B. D. Esry, Phys Rev. Lett. \textbf{99}, 220406 (2007) \\[0pt] [2] J. J. Hua and B. D. Esry, J. Phys. B \textbf{42}, 085601 (2009) [Preview Abstract] |
|
Q1.00123: Carrier-envelope phase control over pathway interference in strong-field dissociation of H$_2^+$ molecular ions M. Zohrabi, Nora G. Kling, K.J. Betsch, S. Zeng, F. Anis, U. Ablikim, Bethany Jochim, Z. Wang, M.F. Kling, K.D. Carnes, B.D. Esry, I. Ben-Itzhak, M. K\"{u}bel The dissociation of an H$_2^+$ molecular-ion beam by linearly polarized, carrier-envelope-phase-tagged 5-fs laser pulses is studied experimentally and theoretically. A coincidence 3D momentum imaging technique is employed to fully characterize the dissociation kinematics. We observe carrier-envelope-phase-dependent asymmetries in the emission direction of H$^+$ fragments relative to the laser polarization for two kinetic energy release regions. These asymmetries are caused by the interference of odd and even photon number pathways [1-2]. In the low kinetic energy region (0.2-0.45 eV), the net-zero-photon and one-photon pathways interfere predominantly while net-two-photon and one-photon interference contributes at the higher kinetic energy region, 1.65-1.9 eV. These measurements are quantitatively compared to ab initio theoretical calculations [1-2] to further our understanding of strong-field coherent control via the carrier-envelope phase.\\[4pt] [1] Nora G. Kling et al. Phys. Rev. Lett. 111, 163004 (2013).\\[0pt] [2] V. Roudnev, B.D. Esry, and I. Ben-Itzhak, Phys. Rev. Lett. 93, 163601 (2004). [Preview Abstract] |
|
Q1.00124: Angle-resolved studies of strong-field ionization and hydrogen elimination from ethylene and ethane A. Voznyuk, D. Schmitz, J. Mahowald, E. Wells, M. Zohrabi, B. Jochim, K.J. Betsch, N.G. Kling, U. Ablikim, T. Severt, B. Berry, K.D. Carnes, I. Ben-Itzhak, R. Siemering, M.F. Kling, R. De Vivie-Riedle Intense few-cycle laser pulses are used to ionize C$_{2}$D$_{4}$ and C$_{2}$D$_{6}$ and stimulate dissociation into C$_{2}$D$_{3}^{+}$ $+$ D and C$_{2}$D$_{5}^{+} + $ D, respectively. Velocity map imaging of the ionized fragment ions allows examination of the angular dependence of these processes. In the ethylene example, calculations show that the HOMO, LUMO, and HOMO-1 orbitals are strongly distorted along the C-D bond direction, leading to the creation of a Rydberg orbital near the deuterium atom. The tunneling ionization probability from the Rydberg orbital is high, explaining the experimental observation of enhanced fragmentation along the C-D bond direction. Similar calculations for ethane show qualitative agreement with the measured angular distributions of C$_{2}$D$_{5}^{+}$ fragments. This link between molecular structure, tunneling ionization, and imaging detection can be useful for image-based adaptive control experiments. [Preview Abstract] |
|
Q1.00125: Significant carrier-envelope phase effects for intense, many-cycle laser pulses Yujun Wang, J.V. Hern\'andez, M. Zohrabi, Ben Berry, U. Ablikim, Nora G. Kling, Travis Severt, Bethany Jochim, K.D. Carnes, I. Ben-Itzhak, B.D. Esry Carrier-envelope phase (CEP) effects in strong-field fragmentation are commonly quantified by the spatial asymmetry of the fragments and have generally been attributed to the spatial asymmetry of the laser's electric field which rapidly vanishes for longer pulses. While this intuitive explanation works reasonably well for straightforward processes like atomic ionization, it fails in general for processes like molecular dissociation. The general theory in [1] was thus developed to provide a universal explanation of CEP effects based on a photon picture. Interestingly, this theory predicts that CEP effects do not depend on a short pulse duration or a field asymmetry, but rather on the laser bandwidth (consistent with a claim in Ref. [2])---largely independent of the pulse length. Our numerical calculations verify this prediction for pulse lengths of at least 10 cycles in both H and H$_2^+$. Moreover, we have experimental verification of this prediction for broad bandwidth lasers chirped up to $\sim$7 cycles---the longest pulse showing CEP effects to date. [1] V. Roudnev and B. D. Esry,Phys. Rev. Lett. 99, 220406 (2007); J. J. Hua and B. D. Esry, J. Phys. B 42, 085601 (2009). [2] T. Nakajima and E. Cormier, Opt. Lett. {\bf 32}, 2879 (2007). [Preview Abstract] |
|
Q1.00126: Defining photon channels in strong-field physics: the photon-phase Fourier representation Shuo Zeng, Mohammad Zohrabi, Ben Berry, Utuq Ablikim, Nora Kling, Travis Severt, Bethany Jochim, Kevin Carnes, Itzik Ben-Itzhak, Brett Esry In strong-field physics, complex atomic and molecular dynamics can be steered by the carrier-envelope phase (CEP). The general theory formulated in Refs. [1,2], provides a rigorous foundation upon which this understanding might be built. By recognizing the underlying periodicity of the time-dependent Schr\"odinger equation---and thus its solutions---in the CEP, {\em all} CEP effects can be understood as the interference of different photon channels [1,2]. We will show that this understanding can be turned around to extract information on the photon channel by examining the CEP dependence. In particular, by taking the Fourier transform with respect to the CEP, photon channel information can be extracted from both theory and experiment. Through several examples, we will also show that this technique can be applied to any system and provides knowledge of the net numbers of photons absorbed---even in few-cycle pulses---that is not available in any other way. [1] V. Roudnev and B. D. Esry, Phys. Rev. Lett. {\bf 99}, 220406 (2007) [2] J. J. Hua and B. D. Esry, J. Phys. B {\bf 42}, 085601 (2009) [Preview Abstract] |
|
Q1.00127: Achieving a quantitative understanding of carrier-envelope phase effects in the benchmark H$_2^+$ molecule Shuo Zeng, Nora Kling, Kelsie Betsch, Mohammad Zohrabi, Fatima Anis, Utuq Ablikim, Bethany Jochim, Zhenhua Wang, Matthias Kuebel, Matthias Kling, Kevin Carnes, Brett Esry, Itzik Ben-Itzhak The implementation of carrier-envelope phase (CEP) control over H$_2^+$ provides an ideal opportunity for a detailed, benchmark comparison of theory and experiment. Given complete experimental inputs, theory should, in principle, be able to reproduce the measured observables quantitatively. Nevertheless, the agreement in Ref. [1] was less than satisfactory. To try to explain the discrepancies, we theoretically consider (i) a non-Gaussian laser spectrum and (ii) the contribution of $n \ge 2$ manifolds and ionization. These two effects will be shown to produce non-trivial changes in the observables. \\[4pt] [1] N. G. Kling {\it et al}, Phys. Rev. Lett. {\bf 111}, 163004 (2013). [Preview Abstract] |
|
Q1.00128: Influence of initial angular distribution on strong-field molecular dissociation Youliang Yu, Shuo Zeng, Yujun Wang, Brett Esry Although there is considerable effort to obtain the dependence of molecular ionization on the nuclear geometry, there have been essentially no studies examining the dependence of dissociation on the nuclear geometry. One would expect, however, that dissociation would also be rather sensitive to the initial disposition of the nuclei. Of the studies that do exist, the vast majority are for reduced-dimensional models and are thus generally of little value in quantitatively predicting what might be seen experimentally. To rectify this situation, we will present full-dimensional numerical solutions of the time-dependent Schr\"odinger equation for strong-field dissociation of H$_2^+$ at intensities where ionization can be neglected. We will examine the dependence of the final momentum distribution and other observables on various initial angular distributions in few-cycle pulses. [Preview Abstract] |
|
Q1.00129: Dissociation of LiF in intense, ultrafast laser pulses Brandon Rigsbee, Brett Esry The alkali-halide family of molecules are of particular interest to study with intense, ultrafast lasers. In general, the lowest two electronic states correspond to an ionic ground state and covalent excited state that cross, giving rise to charge-exchange transitions. The Coulomb potential of the ground state exhibits a dense Rydberg series of vibrational states that are coupled to the covalent excited state at energies above the (diabatic) neutral fragment threshold. Probing this rich structure and controlling the preference between the ionic and covalent properties of the molecule is the focus of this work. We numerically solve the time-dependent Schr\"odinger equation for LiF subject to intense, few-cycle laser pulses to calculate branching ratios and energy spectra for the neutral and ionic fragments. These observables are examined as a function of the laser parameters, including the carrier-envelope phase, to explore the dominant mechanisms of dissociation. [Preview Abstract] |
|
Q1.00130: Laser-assisted XUV few-photon double ionization of helium atoms: joint angular distributions Aihua Liu, Uwe Thumm We have studied the multi-(XUV+IR)-photon double ionization of helium by solving the fully dimensional time-dependent Schr{\"o}dinger equation within a finite-element discrete-variable-representation scheme. We analyze the joint angular distributions for both equal and unequal energy sharing of the two emitted electrons for XUV-photon double ionization in the presence of a short IR pulse. For equal energy sharing, we find that the assisting IR pulse temporary promotes side-by-side emission and enables back-to-back emission. For unequal energy sharing case, we find enhanced back-to-back emission. [Preview Abstract] |
|
Q1.00131: Film-thickness-dependent attosecond streaking time delays for photoemission from adsorbate-covered surfaces Qing Liao, Uwe Thumm We analyze streaked photoelectron spectra and attosecond time delays for the streaked photoemission the from valence band (VB) and core levels (CLs) of Mg(0001) covered W(110) surfaces within a quantum-mechanical model [1,2]. The relative streaking time delay between Mg(VB) and Mg(2p) CL photoelectrons (PEs) is found to be sensitive to Mg coverage for film thicknesses below $\sim$ 100 layers. The relative streaking time delay between Mg(2p) and W(4f) CL PEs is shown to strongly depend on the Mg film thickness and thus on transport effects of PEs inside this solid, in particular, on the scattering of released PEs off the substrate and thin film lattices. Supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy under Grant No. DE-FG02-86ER13491 and NSF Grant PHY-1068752. \\[4pt] [1] C.-H. Zhang and U. Thumm, Phys. Rev. Lett. \textbf{102}, 123601 (2009). \\[0pt] [2] Q. Liao and U. Thumm, Phys. Rev. Lett. \textbf{112}, 023602 (2014). [Preview Abstract] |
|
Q1.00132: Effect of nuclear vibration on high-order harmonic generation of aligned H$_{2}^{+}$ molecules Dmitry A. Telnov, John Heslar, Shih-I Chu High-order harmonic generation (HHG) spectra have been calculated for H$_{2}^{+}$ molecules aligned in the direction parallel to the polarization of the laser field. We make use of the Jacobi coordinates and neglect the rotation of the nuclei. The remaining time-dependent Schr\"{o}dinger equation is 3D in spatial coordinates, one of them being the internuclear separation and the other two describing the electronic motion. The problem is solved using the accurate and efficient time-dependent generalized pseudospectral method in prolate spheroidal coordinates for the electronic coordinates and Fourier grid method for the internuclear separation. Laser pulses with the carrier wavelength of 800 nm, duration of 10 optical cycles, and several peak intensities have been used in the calculations. Our HHG spectra obtained fully beyond the Born-Oppenheimer approximation generally exhibit a significant deviation from those calculated for the fixed internuclear separations. The low-energy regions of the spectra, however, resemble those for the nuclei fixed at larger separations while the high-energy regions are closer to those for the nuclei fixed at smaller internuclear distances. The dynamics of the nuclear vibrational wave packet is also obtained and analyzed. [Preview Abstract] |
|
Q1.00133: Sub-cycle dynamics of multiphoton ionization Dmitry A. Telnov, K. Nasiri Avanaki, Shih-I Chu Sub-cycle oscillatory structures are revealed in calculated time-dependent multiphoton ionization rates. Both atomic and molecular targets manifest multiple ionization bursts per one optical cycle of the laser field. Using the accurate and efficient time-dependent generalized pseudospectral method to solve the time-dependent Schr\"{o}dinger equation, we have performed calculations on H, He$^{+}$, H$_{2}^{+}$, and HHe$^{2+}$, for the laser fields with several intensities and wavelengths in the near-infrared range (750 nm to 1064 nm). The sub-cycle structures appear a universal feature of multiphoton ionization and become well pronounced for sufficiently strong laser fields depending on the target atom or molecule. Analysis of the electron density distributions on the sub-femtosecond time scale shows several time moments per optical cycle (not necessarily corresponding to the peak values of the laser field) when significant portions of the electron density move away from the nucleus giving rise to the bursts in the ionization rate. The nature of the phenomenon can be related to ionization through different pathways, including direct ionization as well as population of the excited states by the laser field with subsequent ionization at later times. [Preview Abstract] |
|
Q1.00134: Multiphoton ionization and high-order harmonic generation of H$_{2}^{+}$ in intense ultrashort elliptically polarized laser fields Kobra Nasiri Avanaki, Shih-I Chu, Dmitry A. Telnov We present an \textit{ab initio} 3D calculation of multiphoton ionization (MPI) and high-order harmonic generation (HHG) of the hydrogen molecular ion subject to intense elliptically polarized laser pulses. The numerical procedure involves the extension of the generalized pseudospectral (GPS) method for non-uniform spatial discretization of the Hamiltonian and wave functions in prolate spheroidal coordinates; the time propagation scheme is based on the split-operator technique in the energy representation. The calculations are performed for the ground and first excited electronic states of H$_{2}^{+}$ at the equilibrium internuclear separation $R = 2$ a.u. as well as for the stretched molecule at $R = 7$ a.u. The dependence of the HHG spectra on the ellipticity parameter is analyzed. The spectral and temporal structures of the HHG signal are studied by means of the wavelet time-frequency analysis. The results provide new insights regarding the detailed HHG mechanisms in elliptically polarized laser fields. [Preview Abstract] |
|
Q1.00135: Sub-Cycle Dynamics of High Harmonic Generation of He Atoms Excited by Attosecond Pulses and Driven by Near-Infrared Laser Fields: A Self-Interaction-Free TDDFT Theoretical Approach John Heslar, Dmitry A. Telnov, Shih-I Chu In the framework of the \textit{self-interaction-free} time-dependent density functional theory, we have performed 3D \textit{ab initio} calculations of He atoms in near-infrared (NIR) laser fields subject to excitation by a single extreme ultraviolet (XUV) attosecond pulse (SAP). We have explored the novel dynamical behavior of the sub-cycle high harmonic generation (HHG) for transitions from the excited states to the ground state and found oscillation structures with respect to the time delay between the SAP and NIR fields. The oscillatory pattern in the photon emission spectra has a period of 1.3 fs which is half of the NIR laser optical cycle, similar to that recently measured in the experiments on transient absorption of He (M. Chini \textit{et al}., Sci. Rep. \textbf{3}, 1105 (2013)). We present the photon emission spectra from 1s2p, 1s3p, 1s4p, 1s5p, and 1s6p excited states as functions of the time delay. We explore the sub-cycle Stark shift phenomenon in NIR fields and its influence on the photon emission process. Our analysis reveals several new features of the sub-cycle HHG dynamics and we identify the mechanisms responsible for the observed peak splitting in the photon emission spectra. [Preview Abstract] |
|
Q1.00136: Role of laser-driven electron multi-scattering in resonance-enhanced below-threshold harmonic generation of He atoms Peng-Cheng Li, Shih-I Chu We perform an \textit{ab initio} study of the resonance-enhanced harmonic generation of He atoms below the ionization threshold by solving the time-dependent Schr$\backslash $"odinger equation and Maxwell's equation simultaneously. An accurate angular-momentum-dependent model potential is constructed for the description of the He atoms low-lying and Rydberg states. We find that the process of laser-driven electron multi-scattering can play a crucial role in resonance-enhanced below-threshold harmonic generation. This result is confirmed by simulations with an extended semiclassical model and time-frequency analysis of macroscopic harmonic spectra by means of the synchrosqueezed transform based on short time Fourier transform. Our results emphasize that the laser-driven electron multi-scattering must be taken into account to fully understand the quantum path contribution related to resonance-enhanced below-threshold harmonic spectra. [Preview Abstract] |
|
Q1.00137: Sub-20 isolated ultrashort attosecond pulse generation from He atoms by two-color mid-infrared laser fields Peng-Cheng Li, Shih-I Chu We propose an efficient method for the generation of ultra-broadband supercontinuum spectra and isolated ultrashort attosecond laser pulse from He atoms with two-color mid-infrared laser fields. High-order harmonic generation (HHG) is obtained by solving the time-dependent Schr$\backslash $"odinger equation accurately by means of the time-dependent generalized pseudospectral method. We found that the optimizing two-color mid-infrared laser pulse allows the HHG cutoff to be significantly extended, leading to the production of ultra-broadband supercontinuum. As a result, an isolated 18 attosecond pulse can be generated directly by the superposition of the supercontinuum harmonics. To facilitate the exploration of the ultrashort attosecond generation mechanisms, we perform both the semiclassical simulation and the wavelet time-frequency transform. [Preview Abstract] |
|
Q1.00138: Generation of short and intense isolated Attosecond pulses by field-controlled excited states Hossein Z. Jooya, Peng-Cheng Li, Sheng-Lun Liao, Shih-I Chu A new mechanism for the coherent control of the generation of an isolated and ultrashort attosecond laser pulse with enhanced intensity is reported. Frequency and time delay of a weak high harmonics, added to a two color laser, are optimized to produce a 45 attosecond pulse with intensity of more than 70 times bigger than the original one. Resonance excitation and subsequent ionization are analyzed, along with electron trajectory investigation from wavelet time-frequency profile to explain the mechanism of the observed augmentation in this high-harmonic generation. [Preview Abstract] |
|
Q1.00139: Below-threshold Harmonic Generations of Aligned Hydrogen Molecular Ions Shih-I Chu, Fu-Yuan Jeng, Yae-Lin Sheu We perform \textit{ab initio} 3D quantum calculations of harmonic generations of the hydrogen molecular ions exposed to intense linearly polarized laser pulses. To fully understand the quantum path contributions related to below-threshold harmonics, the laser-driven electron multi-scattering must be considered. We also find that the orientation of the molecular axis with respect to the polarization of the laser field strongly affect the electron returning times. These results are confirmed by generalized semiclassical simulations and time-frequency analysis of harmonic spectra by means of synchrosqueezed transform based on short-time Fourier transform. [Preview Abstract] |
|
Q1.00140: Floquet calculation of high harmonic generation from hydrogen molecular ions in monochromatic strong laser fields Tsogbayar Tsednee, Marko Horbatsch We extended previous Floquet calculations [1] to obtain high harmonic generation (HHG) for the lowest two electronic states of the $\mbox{H}_2^+$ ion by strong continuous-wave laser fields. We solve the non-hermitean matrix problem to get accurate solutions to the time-dependent Schr\"odinger equation (TDSE) by applying a pseudospectral representation combined with a complex absorbing potential method. This represents an alternative approach to direct TDSE solutions to obtain the harmonic generation spectra for the ion. We compare our results for the HHG rate for the lower and upper states for the $\mbox{H}^{+}_{2}$ ion, which correspond to gerade and ungerade states in the field-free case, with previously obtained results in the literature. We show that the enhancement of the ionization rates at critical internuclear separations $R_{c}$ cause an enhancement of the HHG rates for the lower and upper states. \\[4pt] [1] Ts. Tsogbayar and M. Horbatsch, J. Phys. B \textbf{46}, 46, 245005 (2013) [Preview Abstract] |
|
Q1.00141: Electron momentum distributions from H(1s) ionized by circularly polarized laser pulses Marko Horbatsch, Mitsuko Murakami Recently a 3d computer code for the time-dependent Schr\"odinger equation was developed to deal with the problem of high harmonic generation in orthogonal two-color laser fields [1]. This code has been extended to collect the ionized electron flux in the outer spatial region and to implement a Volkov-type momentum space evolution. This code is used to analyze H(1s) atoms exposed to several-cycle circularly polarized laser pulses in the $10^{14}$ W cm$^{-2}$ intensity regime. The main interest of the work is to investigate systematics in the electron momentum distributions, and the role of Coulomb interactions, in particular. \\[4pt] [1] M. Murakami, O.Korobkin, M. Horbatsch: Physical Review A {\bf 88}, 063429 (2013) [Preview Abstract] |
|
Q1.00142: Attosecond time delay and confinement resonances in photoionization of endohedral atoms: Xe@C$_{60}$ P.C. Deshmukh, A. Mandal, S. Saha, A.S. Kheifets, V.K. Dolmatov, S.T. Manson A theoretical study of Wigner time delay [1] has been applied to the investigation of confinement resonances [2] that occur generally in the photoionization of confined atoms. Calculations have been performed on the 4d subshell of Xe@C$_{60}$ where the existence of confinement resonances has recently been verified experimentally [3]. The random phase approximation in both the nonrelativistic [4] and relativistic [5] versions, which include significant initial and final state correlation, have been employed in the study. The influence of the C$_{60}$ cage on the atom is represented by a spherical annular well [6], which should be good for inner atomic shells at energies significantly higher than the C$_{60}$ plasmons. The results show that the confinement resonances exhibit significant time delay, as compared to the free atom, confirming the interpretation in terms of multiple scattering of the photoelectron off the walls of the confining shell.\\[4pt] [1] E. P. Wigner, \textit{Phys. Rev.} \textbf{98}, 145 (1955); \\[0pt] [2] J.-P. Connerade, et al, \textit{J. Phys. B} \textbf{33}, 2279 (2000);\\[0pt] [3] R. A. Phaneuf, et al, \textit{Phys. Rev.} A \textbf{88}, 053402 (2013);\\[0pt] [4] M. Ya. Amusia, \textit{Atomic Photoeffect} (Plenum, NY, 1990);\\[0pt] [5] W. R. Johnson and C. D. Lin, \textit{Phys. Rev. A} \textbf{20}, 964 (1979);\\[0pt] [6] V. K. Dolmatov, Adv. Quantum. Chem. \textbf{58}, 13 (2009);\\[0pt] [7] A. S. Kheifets, Phys. Rev. A\textbf{ 87}, 063404 (2013). [Preview Abstract] |
|
Q1.00143: Lifetimes and Fano asymmetry parameters of inter-Coulombic decay resonances in photoionization of Ar@C$_{60}$ Mohammad Javani, Steven T. Manson, Mohamed E. Madjet, Himadri S. Chakraborty In a theoretical study of the photoionization of Ar@C$_{\mathrm{60}}$ we find evidence of inter-Coulombic decay (ICD) probability of Ar single-core-electron excited states through degenerate ionization continua of the encapsulating fullerene [1]. Resonances from the ``backward ICD,'' namely, the decay of C$_{60}$ photoexcited inner holes through Ar 3s ionization are also detected. We further predict abundance of a new type of resonance from the interference between concurrent autoionizing and ICD processes that can be termed as resonant hybridized Auger-ICD [2]. Calculations are carried out on a framework of the time-dependent local density approximation where the fullerene ion core of sixty C$^{4+}$ ions is smudged into a continuous jellium distribution [3]. All these classes of resonances assume significantly different shapes from each other and from those of the pure autoionizing resonances of both Ar and C$_{60}$. The resonances are fit to Fano profiles in order to calculate their lifetime, strength and Fano asymmetry parameter q and compare with the regular autoionizing resonances. [1] V. Averbukh and L.S.Cederbaum, \textit{Phys. Rev. Lett.} \textbf{96}, 053401 (2006); [2] M.H. Javani, J.B. Wise, R. De, M.E. Madjet, S.T. Manson, and H.S. Chakraborty, arXiv:1312.2144~[physics.atm-clus]; [3] M.E. Madjet, T. Renger, D.E. Hopper, M.A. McCune, H.S. Chakraborty, J.-M. Rost, and S.T. Manson, \textit{Phys. Rev. A} \textbf{81}, 013202 (2010). [Preview Abstract] |
|
Q1.00144: The quantum confinement resonances of a Xe atom encapsulated inside fullerenes Zhifan Chen, Alfred Z. Msezane The quantum confinement resonances of a Xe atom encapsulated inside C$_{60}$, C$_{80}$, C$_{180}$, and C$_{240}$ have been investigated. The geometric optimization for these fullerenes was performed using the DMol$_3$ software package with the GGA PBE exchange-correlation functional along with all electron double numerical basis sets as implemented in the software package [1]. The measured average radii of the C$_{60}$, C$_{80}$, C$_{180}$, and C$_{240}$ are respectively, 3.5 {\AA}, 4.1 {\AA}, 6.3 {\AA}, and 7.1 {\AA}. Each optimized structure was then introduced into a supercell. The linear response of the ground state to an external perturbation by an electric field was evaluated using the TDDFT method. The locations of the peaks for the confinement resonances calculated by the TDDFT method were compared with the locations estimated using the equation $E(eV) = 67.55+({12.25n \over 2r})^2$, where r is the radius in {\AA} of the fullerene and $n=2,3,4,5,$ etc. The results demonstrate that if the radius of a fullerene equals to an integer ($\ge 2$) $\times$ the half wave length of the photoelectron, then at this photon energy we may be able to observe a confinement peak.\\[4pt] [1] DMol$_3$, Accelrys Software (Inc., San Diego, CA 2010) [Preview Abstract] |
|
Q1.00145: The photoabsorption spectra of a Xe atom encapsulated inside C$_{54}$, C$_{56}$, and C$_{58}$ fullerenes Zhifan Chen, Alfred Z. Msezane The photoabsorption spectra of a Xe atom encapsulated inside C$_{54}$, C$_{56}$, and C$_{58}$ have been investigated using the time-dependent-density-functional-theory (TDDFT). The most stable isomers for these fullerenes are respectively, C$_{54}$ C$_{2v}$:540, C$_{56}$ C$_s$:864, and C$_{58}$ C$_{3v}$:1205. The stuctures of these fullerenes have been created using the Fullerene4.4 [1] package. The structures are then optimized using DMol$_3$ software. The absolute photoabsorption cross sections of C$_{54}$, C$_{56}$, C$_{58}$ and Xe@C$_{54}$, Xe@C$_{56}$, Xe@C$_{58}$ are evaluated using TDDFT. The results demonstrate that, except for the Xe atom inside C$_{58}$, which has similar confinement resonances as those of Xe@C$_{60}$, the Xe atoms inside C$_{54}$ and C$_{56}$ have totally different spectra. Because of this the measured spectra, with the loss of one or more pairs of C atoms, may be affected by the spectra of the Xe inside C$_{54}$ (or C$_{56}$, C$_{58}$). More discussions about the spectra of fullerenes and endohedral fullerenes will be presented at the conference.\\[4pt] [1] P. Schwerdtfeger et al J. Comput. Chem. 35 1508 (2013). [Preview Abstract] |
|
Q1.00146: Photoionization of Li$_2$ Y. Li, M.S. Pindzola, C.P. Ballance, J. Colgan Single and double photoionization cross sections for Li$_2$ are calculated using a time-dependent close-coupling method. The correlation between the outer two electrons of Li$_2$ is obtained by relaxation of the close-coupled equations in imaginary time. Propagation of the close-coupled equations in real time yields single and double photoionization cross sections for Li$_2$. The two active electron cross sections are compared with one active electron distorted-wave and close-coupling results for both Li and Li$_2$. [Preview Abstract] |
|
Q1.00147: Photoionization of Ne$^{8+}$ M.S. Pindzola, Sh. A. Abdel-Naby, F. Robicheaux, J. Colgan Single and double photoionization cross sections for Ne$^{8+}$ are calculated using a non-perturbative fully relativistic time-dependent close-coupling method. A Bessel function expansion is used to include both dipole and quadrupole effects in the radiation field interaction and the repulsive interaction between electrons includes both the Coulomb and Gaunt interactions. The fully correlated ground state of Ne$^{8+}$ is obtained by solving a time-independent inhomogeneous set of close-coupled equations. Propagation of the time-dependent close-coupled equations yields single and double photoionization cross sections for Ne$^{8+}$ at energies easily accessible at advanced free electron laser facilities. [Preview Abstract] |
|
Q1.00148: Single and Double Photoionization of Mg Shahin Abdel-Naby, M.S. Pindzola, J. Colgan Single and double photoionization cross sections for Mg are calculated using a time-dependent close-coupling method. The correlation between the two $3s$ subshell electrons of Mg is obtained by relaxation of the close-coupled equations in imaginary time. An implicit method is used to propagate the close-coupled equations in real time to obtain single and double ionization cross sections for Mg. Energy and angle triple differential cross sections for double photoionization at equal energy sharing of $E_1 = E_2 = 16.4$ eV are compared with Elettra experiments and previous theoretical calculations [1].\\[4pt] [1] E. Sokell \emph{et al.}, Phys Rev. Letts. {\bf 110}, 083001 (2013). [Preview Abstract] |
|
Q1.00149: Physics and Chemistry in High-frequency Strong Laser Fields P. Balanarayan, Nimrod Moiseyev In high frequency strong laser fields the oscillating electrons in an atom behave like they are moving not in a field induced by a positive point charge of the nucleus but in a field which is smeared along the polarization direction of the light and it is peaked at +/- of the quiver length (defined as the ratio between the maximum field amplitude and the square of the laser frequency multiplied by the mass of the electron). We show that for many electron atoms (such as sulfur and oxygen) the ground state of the laser dressed atom has a long lifetime and can be degenerated. \textit{Hence, a strong linear Stark effect rather than the usual quadratic one is obtained}. We show that also a new type of chemical reactions is induced by the high frequency strong laser fields. For example, strong chemical bond (dissociation energy is more than 12 eV) is generated between two helium atoms with a bond length of 2 Angstroms. \textit{Similarly a strong chemical bond is created between sulfur and helium atoms which is somehow similar in its nature to the chemical bond in OH radicals}. \\[4pt] P. Balanarayan and N. Moiseyev, ``Strong chemical bond of stable He2 in strong linearly polarized laser fields,'' Phys. Rev. A \textbf{85}, 032516 (2012).\\[0pt] P. Balanarayan and N. Moiseyev, ``Chemistry in high-frequency strong laser fields: the story of HeS molecule,'' Mol. Phys. \textbf{111}, 1814 (2013).\\[0pt] P. Balanarayan and N. Moiseyev, ``Linear Stark effect for sulfur atom in strong high frequency laser fields,'' Phys. Rev. Lett. \textbf{110}, 253001 (2013). [Preview Abstract] |
|
Q1.00150: Wavelength sensitive detector based on ICD in two coupled quantum wells Tamar Goldzak, Ido Gilary, Nimrod Moiseyev We design a wavelength sensitive detector based on inter coulombic decay (ICD) mechanism in a two-quantum well nano-structure. The two coupled quantum wells are designed to satisfy the specific conditions which allow the ICD to occur. In this setup, by absorbing light an electron in one well is excited. Its relaxation back to the ground state is a non-radiative process which transfers the excess energy to the ionization of the electron in the neighboring well into the continuum. Only radiation with a specific wavelength will be absorbed, when the wavelength matches the excitation energy in the quantum well. By applying a weak bias a current is obtained even when light with a very low intensity is absorbed. For the ICD to be dominant decay mechanism it must prevail over all other possible competitive decay processes. We have found that the lifetime of the ICD is on the timescale of picoseconds. Control over the ICD lifetime can be achieved by variation of different parameters in the two quantum well nano-structure. The most useful parameter is the distance between the two quantum wells. We show that as the distance decreases the decay rate of the ICD increases. Furthermore the distance can be tuned such that the emitted electron would be in a metastable state in the continuum (a resonance state); this causes the life time of the ICD to be an order of magnitude smaller, and improves the efficiency of the ICD. [Preview Abstract] |
|
Q1.00151: Characteristic footprints of an Exceptional Point in the Dynamics of Li Dimer Under a Laser Field Idan Haritan, Ido Gilary, Zohar Amitay, Nimrod Moiseyev The coupling of electronic surfaces induced by laser fields can mix between ro-vibrational bound and continuum states. This mixing leads to a metastable state often called resonance, characterized by a finite lifetime. As shown here, for specific values of the laser frequency and intensity, two resonances can become degenerate. This type of degeneracy is very different in its nature from the bound states' degeneracy, and is known as an exceptional point (EP). An EP holds unique characteristics. One of which is a switch like behavior. Our numerical studies show that by varying adiabatically the laser parameters in a closed loop around the EP, one resonance of the Li dimer permutes with another resonance. Given all of the above, it is clear why finding footprints of this exceptional phenomenon is of the essence. For a Li dimer the cw laser field couples the X, A and E electronic surfaces of the molecule, and thus creating an EP. We show how one can probe the EP by varying the laser intensity in the specific frequency of the EP. Finally, as a conjecture based on this numerical study, we suggest that the footprints of this EP might be reflected in a simple measurement - by the amount of molecules that dissociate. The fraction of the dissociated molecules will abruptly reduce once the EP is reached. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700