Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z29: A Potpourri of AMO and Quantum Information |
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Sponsoring Units: DAMOP Chair: Laith Haddad, Colorado School of Mines Room: C123 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z29.00001: Towards Hybrid Quantum Information Processing with Electrons on Helium Andreas Fragner, David Schuster, Mark Dykman, Stephen Lyon, Robert Schoelkopf Electrons on helium is a unique system in which a two-dimensional electron gas is formed at the interface of a quantum liquid (superfluid helium) and vacuum. As outlined in our recent proposal [1], single-electron quantum dots on helium can be built using submerged electrostatic gates and the lateral motion of the electron can be coupled to the electromagnetic field in a superconducting resonator by integrating the quantum dot into a circuit QED architecture [2]. Energy can be exchanged coherently between motional states and individual photons at an estimated Rabi frequency of $g/2\pi\sim 20$ MHz while motional and spin coherence times exceed 20 $\mu$s for charge and 1 s for spin with a spin-photon coupling as high as 1 MHz [1,3], making the system attractive for quantum information processing. Here, I will present recent experimental progress towards trapping and detecting single electrons on helium with a high-finesse superconducting cavity.\\[4pt] [1] D.I. Schuster, et al. in preparation (2009) \newline [2] A. Wallraff, et. al. Nature 431, 162 (2004) \newline [3] S. A. Lyon, Phys. Rev. A 74, 052338 (2006) [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z29.00002: Electron occupancy of micro-structured helium-filled channels Maika Takita, F.R. Bradbury, S.A. Lyon The spins of electrons floating on the surface of superfluid helium have been suggested to be promising qubits. High charge transfer efficiency of electrons in a narrow channel clocked with underlying gates, has been previously reported.\footnote{G. Sabouret, F.R. Bradbury, S. Shankar, J.A. Bert, S.A. Lyon, Appl. Phys. Lett. \textbf{92}, 082104 (2008).} We have fabricated similar devices with an array of parallel channels and small gaps between the underlying gates. These channels are filled with superfluid helium by capillary action, onto which electrons are photoemitted. Electrons are initially trapped by a gate (``door''), so that they capacitively couple to a sense gate which is the input of a cold HEMT preamplifier. An oscillatory potential applied to a third gate moves electrons on and off the sense gate to allow lock-in detection. Electrons are allowed to escape the sensing region by slowly ramping down the door barrier. Features in the electron occupancy signal correlate with the oscillatory drive voltage and preamp gain, and show evidence of discrete occupancy as the channels depopulate. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z29.00003: Exploiting silicon chip technology for control of electrons on superfluid helium F.R. Bradbury, Maika Takita, Kevin Eng, T.M. Gurrieri, K.J. Wilkel, S.A. Lyon Electrons on the surface of superfluid helium have extremely high mobilities and long predicted spin coherence times, making them ideal mobile qubits. Previous work has shown that electrons localized in helium filled channels can be reliably transported between multiple underlying gates. Silicon chips have been designed, fabricated, and post processed by reactive ion etching to leverage the large scale integration capabilities of silicon technology. These chips, which serve as substrates for the electrons on helium research, utilize silicon CMOS for on-chip signal amplification and multiplexing and the uppermost metal layers for defining the helium channels and applying electrical potentials for moving the electrons. We will discuss experimental results for on-chip circuitry and clocked electron transport along etched channels. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z29.00004: Spin and Orbital Rotation of Electrons and Photons via Spin-Orbit Interaction Cody Leary, Michael Raymer, Steven van Enk We show that when an electron or photon propagates in a cylindrically symmetric waveguide, its spin angular momentum (SAM) and its orbital angular momentum (OAM) interact. Remarkably, we find that the dynamics resulting from this spin- orbit interaction are quantitatively described by a single expression applying to both electrons and photons. This leads to the prediction of several novel rotational effects: the spatial or time evolution of either particle's spin/polarization vector is controlled by its OAM quantum number, or conversely, its spatial wavefunction is controlled by its SAM. We show that the common origin of these effects in electrons and photons is a universal geometric phase. We demonstrate how these phenomena can be used to reversibly transfer entanglement between the SAM and OAM degrees of freedom of two-particle states. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z29.00005: Positronium Cooling in Porous Silica Measured via Doppler Spectroscopy Tomu Hisakado, David Cassidy, Allen P. Mills, Harry W. K. Tom We have measured the kinetic energy of positronium (Ps) atoms emitted into vacuum from a porous silica film subsequent to positron bombardment, via the Doppler spread of the line width of the Ps 13S-23P transition. We find that the deeper in the target film that positrons are implanted the colder is the emitted Ps, an effect we attribute to cooling via collisions in the pores as the atoms diffuse back to the film surface. We observed a lower limit to the mean Ps kinetic energy associated with motion in the direction of the laser, \textit{Ex }= 42 $\pm $ 3 meV, that is consistent with conversion of the confinement energy of Ps in the 2.7 nm diameter pores to kinetic energy in vacuum. An implication is that a porous sample would need to be composed of pores greater than around 10 nm in diameter in order to produce thermal Ps in vacuum with temperatures less than 100K. By performing Doppler spectroscopy on intense pulses of Ps we have experimentally demonstrated the production of many excited state Ps atoms simultaneously, which could have numerous applications, including laser cooling and fundamental spectroscopic studies of Ps and the production of antihydrogen. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z29.00006: Cooling Atoms with a Moving One-Way Barrier Jeremy Thorn, Elizabeth Schoene, Daniel Steck We demonstrate the use of a moving optical one-way barrier for cooling a collection of atoms. In our experiment, rubidium atoms begin in a far-detuned dipole trap consisting of a single focused Gaussian beam. Two laser beams transversely cross the trap; one provides a repulsive (attractive) potential for atoms in the upper (lower) ground state, and the other pumps atoms into the upper ground state on one side of the first beam, forming a one-way barrier. The optical one-way barrier is adiabatically swept along the longitudinal axis of the trap. At each point, the barrier traps atoms near their turning point, where they have less kinetic energy. As the barrier sweeps, the atoms do not regain their kinetic energy, and are eventually left at the trap focus with less kinetic energy than before. We experimentally study the effectiveness of barrier-cooling, focusing on how experimental limitations affect the cooling limit. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z29.00007: Recombination of N bosons near threshold Nirav Mehta, Seth Rittenhouse, Jose D'Incao, Javier von Stecher, Chris Greene We derive a generalized cross section for scattering events involving an arbitrary number of particles, and apply our result to the recombination of N bosons. We obtain a semi-analytical formula that encapsulates the overall Wigner threshold scaling as well as resonant enhancements due to the presence of N-body states near threshold. For the case N=4, we obtain quantitative results for the event rate that exhibit resonant enhancement due to known universal 4-boson states tied to Efimov physics. [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z29.00008: Universality in Three- and Four-Body Bound States of Ultracold Atoms S. E. Pollack, D. Dries, R. G. Hulet The universal regime of Efimov few-body physics occurs when the strength of the interparticle interaction is much larger than the effective range of the two-body potential. By exploiting a broad Feshbach resonance in the $|1,1\rangle$ hyperfine state of $^7$Li, we can tune the interactions well into the universal regime. The rate of atom loss from our optical trap increases by 9 orders of magnitude from the weakly interacting regime to the strongly interacting regime, allowing unprecedented access to universal physics. We find evidence for two universally connected Efimov trimers in addition to their associated four-body bound states. Intimately related to the Efimov trimers, two tetramer states exist for each trimer, and no additional parameters are required to describe their binding energies. A total of eleven features in the three- and four-body inelastic loss spectra are discovered. The relative locations of these features on either side of the Feshbach resonance agree with universal theory, whereas a systematic deviation from universality is found when comparing features across the resonance. Science.1182840 (2009). [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z29.00009: Nonlinear optical response and ionization of a metal tip plasmon in ultrafast strong fields Shawn Perdue, Joonhee Lee, Desire Whitmore, Alejandro Rodriguez Perez, V. Ara Apkarian The nonlinear response of a silver tip plasmon is investigated by simultaneously measuring its optical response and field induced ionization current. The measurements rely on interferometric cross-correlation of frequency-modulated optical pulse trains. The method allows for a quantitative analysis of the plasmon nonlinear optical susceptibilities, and a unique interpretation of the ionization process as field induced tunneling. Nonlinear optical mixing up to the 4th harmonic of the Ti:Sapphire fundamental is observed by detecting electron current, demonstrating an electron pulse train of 600 attosecond period. The electron pulse train results from the detachment of the strongly modulated plasmon tail. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z29.00010: Velocity Map Imaging Spectroscopy of the Lanthanide Negative Ions Kiattichart Chartkunchand, Vernon Davis, Jeffrey Thompson, Aaron Covington The technique of Velocity Map Imaging Spectroscopy (VMIS) is being adapted for the study of the heavy negative ions of the Lanthanide series. The VMIS technique will allow us to determine structural properties of these negative ions as well as yield angular distribution information for photon-negative ion interactions. An overview of the experimental apparatus as well as preliminary data on the cerium negative ion Ce$^-$ will be presented. [Preview Abstract] |
Friday, March 19, 2010 1:15PM - 1:27PM |
Z29.00011: Spectral theory for molecules and materials: Pauli revisited Peter W. Langhoff, Michal Ben-Nun, Jeffrey Mills, Jerry Boatz Implementations of new theoretical methods are reported for {\it ab initio} chemical structure calculations of molecules and materials based on an atomic spectral-product representation of aggregate electronic degrees of freedom. In this approach, the Pauli principle is enforced subsequent to construction of the Hamiltonian representative matrix in the basis, greatly simplifying its evaluation. It is shown that atomic pair-interaction calculations, which can be performed once and for all and retained for repeated applications, are sufficient to determine the electronic eigenstates and chemical structures of arbitrary chemical aggregates. The spectral-product representation is seen to span the totally antisymmetric representation of the aggregate electron symmetric group once and only once, but to also span other non-Pauli representations in which the desired Pauli solutions of the Schr\"odinger equation are generally embedded. Progress in isolating totally antisymmetric solutions is described employing the antisymmetrizer matrix constructed in the spectral-product basis. The Pauli subspace of the full spectral-product Hilbert space is isolated in this manner, and the corresponding physical block of the aggregate Hamiltonian matrix determined. Illustrative calculations of ground- and excited-state potential energy surfaces in simple molecules exhibit convergence to corresponding totally antisymmetric results. [Preview Abstract] |
Friday, March 19, 2010 1:27PM - 1:39PM |
Z29.00012: An ``Anatomic approach" to study the Casimir effect Francesco Intravaia, Harald Haakh, Carsten Henkel The Casimir effect, in its simplest definition, is a quantum mechanical force between two objects placed in vacuum. In recent years the Casimir force has been the object of an exponentially growing attention both from theorists and experimentalists. A new generation of experiments paved the way for new challenges and spotted some shadows in the comparison to theory. Here we are going to isolate different contributions to the Casimir interaction and perform a detailed study to shine new light on this phenomenon. As an example, the contributions of Foucault (eddy current) modes will be discussed in different configurations. This ``anatomic approach'' allows to clearly put into evidence special features and to explain unusual behaviors. This brings new physical understanding on the undergoing physical mechanisms and suggests new ways to engineer the Casimir effect. [Preview Abstract] |
Friday, March 19, 2010 1:39PM - 1:51PM |
Z29.00013: Electromagnetic Energy, Absorption, and Casimir Forces Felipe da Rosa, Diego Dalvit, Peter Milonni The derivation of Casimir forces between dielectrics can be simplified by ignoring absorption, calculating energy changes due to displacements of the dielectrics, and only then admitting absorption by allowing permittivities to be complex. As a first step towards a better understanding of this situation we consider in this paper the model of a dielectric as a collection of oscillators, each of which is coupled to a reservoir giving rise to damping and Langevin forces on the oscillators and a noise polarization acting as a source of a fluctuating electromagnetic (EM) field in the dielectric. The model leads naturally to expressions for the quantized EM fields that are consistent with those obtained by different approaches, and also results in a fluctuation-dissipation relation between the noise polarization and the imaginary part of the permittivity. Our main result is the derivation of an expression for the QED energy density of a uniform dispersive, absorbing media in thermal equilibrium. We also show how the fluctuation-dissipation theorem ensures a detailed balance of energy exchange between the (absorbing) medium, the reservoir and the EM field in thermal equilibrium. [Preview Abstract] |
Friday, March 19, 2010 1:51PM - 2:03PM |
Z29.00014: Quantum Phases of Atom-Molecule Mixtures of Fermionic Atoms Nicolas Lopez Valdez, Shan-Wen Tsai, Chi-Yong Lin Cold atom experiments have realized a variety of multicomponent quantum mixtures, including Bose-Fermi atomic mixtures. Mixtures of fermionic atoms and diatomic molecules, which are boson, have also been obtained by tuning of the interactions with external fields [1]. We study many-body correlations in such a system where the molecules are weakly bound and therefore pairs of fermionic atoms easily convert into and dissociate from the bound molecule state. This exchange mediates a long-range interaction between the fermions. We consider a simple many-body Hamiltonian that includes the destruction of fermionic atom pairs to form single bosonic molecules and vice versa [2]. We employ a functional renomalization-group approach and calculate the renormalized frequency-dependent interaction vertices and fermion self-energies. We find an instability from the disordered quantum liquid phase to a BCS phase and calculate the energy scale for the transition. The unusual frequency-dependence of this mediated interaction leads to strong renormalization of the self-energy, and also affects the couplings in the BCS channel. [1] M. Greiner, C. A. Regal, J. T. Stewart, and D. S. Jin, Phys. Rev. Lett. {\bf 94}, 110401 (2005) [2] E. Timmermans, K. Furuya, P. W. Milonni, and A. K. Kerman, Phys. Lett. A {\bf 285}, 228 (2001) [Preview Abstract] |
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