Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Y9: BEC/Matter Optics/Atom Interferometry |
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Sponsoring Units: DAMOP Chair: Conjung Wu, University of California, San Diego Room: Morial Convention Center RO7 |
Friday, March 14, 2008 11:15AM - 11:27AM |
Y9.00001: Phase diagram of a Bose gas near a wide Feshbach resonance Lan Yin The phase diagram of a homogeneous Bose gas with a repulsive interaction near a wide Feshbach resonance is studied at zero temperature. The Bose-Einstein-condensation (BEC) state of atoms is a metastable state. When the scattering length $a$ exceeds a critical value depending on the atom density $n$, $na^3>0.035$, the molecular excitation energy is imaginary and the atomic BEC state is dynamically unstable against molecule formation. The BEC state of diatomic molecules has lower energy, where the atomic excitation is gapped and the molecular excitation is gapless. However when the scattering length is above another critical value, $na^3>0.0164$, the molecular BEC state becomes a unstable coherent mixture of atoms and molecules. (http://arxiv.org/abs/0710.5318)(cond-mat/0710.5318) [Preview Abstract] |
Friday, March 14, 2008 11:27AM - 11:39AM |
Y9.00002: Initial States of BEC mixtures Produced by Cooling in the Presence of a Feshbach Resonance Laura Halmo, Mark Edwards We have studied the types of Bose--Einstein condensate (BEC) mixtures produced as a result of different cooling paths. These results are relevant to a recent experiment in which a mixture of $^{85}$Rb and $^{87}$Rb BECs was cooled in three stages: (1) optical pre--cooling, (2) evaporative cooling in a magnetic trap, and (3) evaporatively cooled in an optical trap. We assume that, upon transfer to the optical trap, the state of the mixture of thermal gases can be represented by the superposition of a small number of low--lying trap eigenstates each with high occupation. In this case, the bose field operator can be approximated as a $c$--number and its evolution will be governed by the nonlinear Schr\"odinger equation. We investigated the density profiles that resulted from different initial thermal distributions as well as non--thermal initial distributions. We also performed studies of the effect of varying the $^{85}$Rb--$^{85}$Rb scattering length via a Feshbach resonance. We found condensate states that differ markedly from the standard Thomas--Fermi ground states of the Gross--Piteavskii equation. [Preview Abstract] |
Friday, March 14, 2008 11:39AM - 11:51AM |
Y9.00003: Interference between atomic Bardeen-Cooper-Schrieffer gases Tun Wang, Susanne Yelin We study the interference between two atomic Bardeen-Cooper- Schrieffer (BCS) gases using noise correlations. Fringes as seen in the interference between two Bose-Einstein Condensates (BECs) do not to exist due to the requirement that two BCS gases have to initially overlap to interfere. This requirement results from the fact that the spin up and spin down fermions in a Cooper pair have opposite momenta. Nevertheless, BCS gases still interfere with each other, and their interference patterns share many aspects with those of BECs. [Preview Abstract] |
Friday, March 14, 2008 11:51AM - 12:03PM |
Y9.00004: Single and double reflection Michelson atom interferometers in a weakly-confining magnetic trap Rudra Kafle, James Stickney, Dana Anderson, Alex Zozulya We analyze the operation of a BEC based atom interferometer, where the atoms are held in a weakly-confining magnetic trap and manipulated with diffraction gratings produced by counter-propagating laser beams. A simple analytic model is developed to describe the dynamics of the interferometer. It is used to find the region of parameters corresponding to high values of the interference fringe contrast for both single and double reflection geometries. We demonstrate that for a double reflection interferometer the coherence time can be increased by shifting the recombination time. Finally, we compare the theory with recent experimental realizations of these interferometers and estimate when phase diffusion and finite temperature phase fluctuations become important. [Preview Abstract] |
Friday, March 14, 2008 12:03PM - 12:15PM |
Y9.00005: Prospects for a Gradient Magnetometer Atom Interferometer Frank A. Narducci, Jon P. Davis Atom interferometers form the basis for state-of-the-art sensors, including gravimeters, gravity gradiometers, gyroscopes and atomic clocks. Notably absent from this list are magnetometers, which can have a wide range of applications ranging from military to medical applications. We propose a scheme to realize an atom interferometer {\em gradient} magnetometer. We begin by demonstrating a light-pulse magnetic beam-splitter. The analysis is based on a full multi-level 2-laser field Maxwell-Bloch model including state selection rules, polarization selectivity, laser detuning, and Doppler averaging. We then consider an ensemble of atoms subject to a $\pi/2-\pi-\pi/2$ pulse sequence. The phase of the interference pattern depends on the phase of the action along the classical path and on the phase of the combined laser fields imprinted on the atoms during the pulse sequence. From this analysis, we conclude that, to first order, the phase of the interferometer output is insensitive to the field across the interferometer, but is sensitive to the {\em gradient} of the field. Using realizable numbers from existing interferometers, we show that a gradient magnetometer of this type has can have a greater gradient sensitivity than many current magnetic sensors. We discuss the status of our current experiments using ultra-cold atoms. [Preview Abstract] |
Friday, March 14, 2008 12:15PM - 12:27PM |
Y9.00006: Bose--Josephson Junction with Binary Mixture of Bosonic Atoms Mark Edwards, Jeffrey Heward, Indubala Satija, Radha Balakrishnan, Phillip Naudus We consider a bose--Josephson junction consisting of a binary mixture of two weakly coupled Bose--Einstein condensates confined in a symmetric double--well external potential. In a single condensate confined in a double--well potential, when the condensate wavefunction is approximated as a linear combination of the lowest two eigenmodes of the potential, the result is a dynamical system analogous to those that describe the current and phase across a Josephson junction. Josephson oscillations and nonlinear self--trapping are among the effects predicted by this dynamical system. Using the same two--mode approximation, the condensate mixture can be mapped to two coupled, non--rigid pendula. Although the system is found to exhibit periodic dynamics, the tunneling dynamics of the individual components can be periodic, quasiperiodic, as well as chaotic. We also investigate the experimental signatures of these effects and the goodness of the two--mode approximation by solving the coupled Gross--Pitaevskii equations that govern the behavior of the system. [Preview Abstract] |
Friday, March 14, 2008 12:27PM - 12:39PM |
Y9.00007: Dynamics of phase separation in cold-atom boson-fermion mixtures Dmitry Solenov, Dmitry Mozyrsky We study the kinetics of the first order phase separation transition in boson-fermion cold atom mixtures. At low enough temperatures such a transition is driven by quantum fluctuations responsible for the formation of critical nuclei of a stable phase. Based on a microscopic description of interacting boson-fermion mixtures we derive an effective action for the critical droplet and obtain an asymptotic expression for the nucleation rate in the vicinity of the phase transition and near the spinodal instability of the mixed phase. We show that in the former case the transition rate is significantly modified by dissipation due to interaction with fermion excitations. The regimes where quantum nucleation can be experimentally observed in cold atom systems are identified. [Preview Abstract] |
Friday, March 14, 2008 12:39PM - 12:51PM |
Y9.00008: Quantum phases of mixtures of atoms and molecules on optical lattices Valy Rousseau, Peter Denteneer We investigate the phase diagram of a two-species Bose-Hubbard model with an additional conversion term, where two particles from the first species can be converted into one particle of the second species, and vice-versa. The model can be related to ultra-cold atoms experiments where Feshbach resonance, used to tune the scattering length, produces long-lived bound states viewed as diatomic molecules. The model is solved exactly by means of Quantum Monte Carlo simulations. We find that the model exhibits an exotic incompressible ``Super-Mott'' phase where the particles from both species can flow with signs of superfluidity, but with anti-correlations such that there is no global supercurrent. [Preview Abstract] |
Friday, March 14, 2008 12:51PM - 1:03PM |
Y9.00009: First order behaviour of Bose Fermi mixtures across a Feshbach resonance Charles Mathy, Francesca Marchetti, Meera Parish, David Huse We analyze the phase diagram of a mixture of bosonic and fermionic atoms, whose interaction is tuned by varying a magnetic field across a Feshbach resonance. To this end, we introduce a two-channel model and study it with a mean field approach. The phase diagram is found to contain both second order and first order phase transitions, which leads to a regime of densities where phase separation is predicted. We explain why our model is consistent with the experimental observation of collapse, which is usually captured by a single- channel model, and discuss in which systems one is most likely to encounter the physics we are describing. [Preview Abstract] |
Friday, March 14, 2008 1:03PM - 1:15PM |
Y9.00010: Boson-Fermion mixture and superconducting phases on the honeycomb lattice Doron Bergman, Peter Orth, Karyn Le Hur We explore theoretically the different phases of a Boson-Fermion mixture in a honeycomb lattice model. With realistic band structure and interactions, we find that much like phonons in a solid, the bosonic atoms induce effective attractive interactions between the fermions. The attractive interactions can then lead to a number of superconducting phases, which we explore. Using a Bogoliubov and mean-field approach, as well as a full RG treatment, we derive the phase diagram. Possible phases of the system include s-wave as well as $p+i p$ superconducting states. We also analyze the nature of the vortices in the different superconducting states, as these are of great interest as a possible realization of emergent non-Abelian statistics. We explain how tuning between different superconducting phases can be achieved in a cold atomic gas realization of this system. [Preview Abstract] |
Friday, March 14, 2008 1:15PM - 1:27PM |
Y9.00011: Supersymmetry and Goldstino-like Mode in Bose-Fermi Mixtures Yue Yu, Kun Yang Supersymmetry is assumed to be a basic symmetry of the world in many high energy theories, but none of the super partners of any known elementary particle has been observed yet. We argue that supersymmetry can also be realized and studied in ultracold atomic systems with a mixture of bosons and fermions, with properly tuned interactions and single particle dispersion. We further show that in such non-releativistic systems supersymmetry is either spontaneously broken, or explicitly broken by a chemical potential difference between the bosons and fermions. In both cases the system supports a sharp fermionic collective mode similar to the Goldstino mode in high-energy physics, due to supersymmetry. We also discuss possible ways to detect this mode experimentally. [Preview Abstract] |
Friday, March 14, 2008 1:27PM - 1:39PM |
Y9.00012: Preemptive phase-transitions in multicomponent BECs Steinar Kragset, Eskil Kulset Dahl, Egor Babaev, Asle Sudbo We use analytical arguments and large-scale Monte-Carlo simulations to investigate phase transitions between various complex superfluid phases in a two-component Bose-Einstein condensate with varying non- dissipative drag between the two components. We focus on establishing the phase- diagram and investigate in detail the individual and composite superfluid densities that the system features, using a representation in terms of the phases of the superfluid ordering fields. In particular, we describe a novel preemptive scenario, whereby drag induces a first-order phase transition from the interplay between two phase-transitions that individually would have been in the $3DXY$-universality class. Our results may shed light on similar phenomena occuring in certain multicomponent superconductors and in scenarios of deconfined quantum criticality in certain quantum antiferromagnetic systems. [Preview Abstract] |
Friday, March 14, 2008 1:39PM - 1:51PM |
Y9.00013: Chaos Threshold in Bose-Hubbard Model Amy Cassidy, Vanja Dunjko, Maxim Olshanii The goal of this work is to determine the criterion for chaos in the one-dimensional mean-field Bose-Hubbard model. We investigate the time evolution of this system with a few low-energy momentum modes excited initially. A threshold for chaos is identified from calculations of the largest Lyapunov exponent, which is compared with the predictions of the Chrikov criterion of overlapping resonances. Additionally, the results are compared with a closely related fully integrable model. [Preview Abstract] |
Friday, March 14, 2008 1:51PM - 2:03PM |
Y9.00014: Quantum quench dynamics in analytically solvable one-dimensional models Anibal Iucci, Miguel A. Cazalilla, Thierry Giamarchi In connection with experiments in cold atomic systems, we consider the non-equilibrium dynamics of some analytically solvable one-dimensional systems which undergo a quantum quench. In this quench one or several of the parameters of the Hamiltonian of an interacting quantum system are changed over a very short time scale. In particular, we concentrate on the Luttinger model and the sine-Gordon model in the Luther-Emery point. For the latter, we show that the order parameter and the two-point correlation function relax in the long time limit to the values determined by a generalized Gibbs ensemble first discussed by J. T. Jaynes [Phys. Rev. \textbf{106}, 620 (1957); \textbf{108}, 171 (1957)], and recently conjectured by M. Rigol \emph{et.al.} [Phys. Rev. Lett. \textbf{98}, 050405 (2007)] to apply to the non-equilibrium dynamics of integrable systems. [Preview Abstract] |
Friday, March 14, 2008 2:03PM - 2:15PM |
Y9.00015: Supercurrent survival under Rosen-Zener quench of hard core bosons Israel Klich, Courtney Lannert, Gil Refael We study the survival of super-currents in a system of impenetrable bosons subject to a quantum quench from its critical superfluid phase to an insulating phase. We show that the evolution of the current when the quench follows a Rosen-Zener profile is exactly solvable. This allows us to analyze a quench of arbitrary rate, from a sudden destruction of the superfluid to a slow opening of a gap. The decay and oscillations of the current are analytically derived, and studied numerically along with the momentum distribution after the quench. In the case of small supercurrent boosts $\nu$, we find that the current surviving at long times is proportional to $\nu^3$ [Preview Abstract] |
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