Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session H2: Disorder in Quantum Gases |
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Chair: Brian DeMarco, University of Illinois Urbana-Champaign Room: Grand Ballroom GF |
Wednesday, June 6, 2012 10:30AM - 10:42AM |
H2.00001: Studies of disordered quasi-2D Bose gasses Matthew Reed, Zack Smith, Steven Rolston We present trapped quasi-2D bose gasses in an optical speckle disorder. The disorder's correlation length, at 1 micrometer, is on the order of the atomic de-Broglie wavelength ($\Lambda$ between 350 and 500 nm) and the healing length (250 to 1000 nm) of our trapped gasses. This is a parameter regime whose properties have been resistant to analytical and numerical study, and in the case of disorder with a nontrivial autocorrelation function, the ground state is unknown. Using one plane as a phase reference for a second, we analyze the coherence properties of the trapped gas by studying both the average phase in the imaging direction and the visibility of the fringes. We correlate a reduction in phase coherence with increased variance of the disorder, and correlate this with both phonon and vortex statistics in both adiabatically prepared samples and in quenched gasses. [Preview Abstract] |
Wednesday, June 6, 2012 10:42AM - 10:54AM |
H2.00002: Disordered Hubbard model with ultracold atoms Stanimir Kondov, William McGehee, Joshua Zirbel, Brian DeMarco We report progress in studying the effects of disorder on the phase diagram of the Hubbard model. The resulting disordered Hubbard model (DHM) is the subject of intense research in condensed matter physics due to its applicability to strongly correlated electronic systems. We realize the DHM using ultracold $^{40}$K atoms in an optical lattice superimposed with a speckle light field. The aim of our study is to explore the variety of metallic and insulating phases which arise in the interplay between kinetic energy, interactions and disorder. [Preview Abstract] |
Wednesday, June 6, 2012 10:54AM - 11:06AM |
H2.00003: Phase Diagram of Commensurate Two-Dimensional Disordered Bose Hubbard Model Sebnem Gunes Soyler, Mikhail Kiselev, Nikolay Prokof'ev, Boris Svistunov We do quantum Monte-Carlo simulations to calculate the full ground state phase diagram of the two dimensional disordered Bose-Hubbard model at unity filling factor. We observe superfluid regions persisting up to large values of disorder and interaction strength. In the vicinity of the superfluid-insulator transition of the pure system, the system shows almost unmeasurable response to weak disorder. [Preview Abstract] |
Wednesday, June 6, 2012 11:06AM - 11:18AM |
H2.00004: Polarons in a strongly interacting Bose-Fermi mixture Cheng-Hsun Wu, Ibon Santiago, Jee Woo Park, Peyman Ahmadi, Sebastian Will, Martin Zwierlein The fate of an impurity interacting with its environment is a fundamental problem in condensed matter physics. The famous example is that of an electron moving in the crystal background of ions, dressing itself with lattice distortions, phonons. In ultracold atomic systems, impurities interacting with a Fermi sea have been studied, leading to the observation of Fermi polarons. Here we study the interaction of an impurity immersed in a Bose-Einstein condensate of $^{23}$Na. We perform radio-frequency spectroscopy on the impurity atom and the bath, which is expected to probe the spectral features characteristic for polaronic dressing: A delta-like peak in addition to a broad pedestal coming from the interactions between the impurity and the phonons in the condensate. A mixture of $^{23}$Na and $^{40}$K with its widely tunable interactions promises to be an ideal system to study the evolution from Bose polarons to Fermi polarons as the imbalance between $^{23}$Na and $^{40}$K is varied. [Preview Abstract] |
Wednesday, June 6, 2012 11:18AM - 11:30AM |
H2.00005: Dynamics of Bose-Einstein condensates and wave chaos Iva Brezinova, Lee A. Collins, Barry I. Schneider, Axel U.J. Lode, Alexej I. Streltsov, Ofir E. Alon, Lorenz S. Cederbaum, Joachim Burgdorfer We study theoretically the expansion of BECs in a one-dimensional trap in the presence of external periodic, aperiodic, and disordered potentials. Disordered potentials are of special interest in the connection of Anderson localization. We investigate the dynamics of BECs within both the Gross-Pitaevskii equation (GPE) as well as the multiconfigurational time-dependent Hartree for bosons (MCDTHB) method. The GPE is strictly valid only for the condensate. We find that for certain potentials the solutions of the GPE exhibit wave chaos as measured by the exponential divergence of nearby wave functions in Hilbert space. We provide numerical evidence for the connection between wave chaos within the GPE and depletion of the condensate. We show that the ability of the GPE to predict the density on length scales of the potential variations is limited by the appearance of wave chaos. Surprisingly, despite a strong depletion of the condensate, coarse-grained observables averaged over larger scales, e.g. the width of the atom cloud, are well reproduced within the GPE. Accordingly, experimental results for these observables may agree with the predictions of the GPE although the system is strongly excited. The depletion can be detected experimentally through decay of coherence. [Preview Abstract] |
Wednesday, June 6, 2012 11:30AM - 11:42AM |
H2.00006: Probing mean-field screening in a tilted incommensurate lattice Jeremy Reeves, Matthias Vogt, Bryce Gadway, Daniel Pertot, Dominik Schneble There has been recent interest in the competing roles of disorder and interactions on the dynamics of ultracold gases in optical lattices. Here, we investigate a weakly interacting Bose-Einstein condensate in a tilted incommensurate lattice potential. It is well known that both collisional interactions and disorder individually cause damping of Bloch oscillations. We explore the interplay between the two damping effects and observe a reduction in the disorder-induced damping rate due to the presence of interactions, consistent with screening of disorder. [Preview Abstract] |
Wednesday, June 6, 2012 11:42AM - 11:54AM |
H2.00007: 3D Anderson Localization in Variable-Scale Speckle Potentials William McGehee, Stanimir Kondov, Joshua Zirbel, Brian DeMarco Anderson localization in three dimensions is controlled by the interplay between a particle's Boltzmann mean free path and its wavelength. We extend our measurement of 3D Anderson localization in an interaction-free, ultracold Fermi gas by varying the mean free path through changes in the correlation length of the disordered potential. The potential is created using optical speckle, and the correlation length is varied over a factor of five. We determine how the correlation length affects the mobility edge and the length scale of localization. [Preview Abstract] |
Wednesday, June 6, 2012 11:54AM - 12:06PM |
H2.00008: Effecvt of Disorder on BCS-BEC Crossover in a Two-dimensional Ultracold Fermi Gas B. Tanatar, Ayan Khan, Saurabh Basu We study the BCS-BEC crossover in a two-dimensional ultracold gas of fermionic atoms in the presence of a weak white noise-like random disorder, whose effects are incorporated in the mean-field treatment via Gaussian fluctuations. Self-consistent computation of the physical properties such as the gap parameter and the condensate fraction reveal that the weakly coupled superfluid is unaffected by disorder, whereas the molecular BEC phase is found to be significantly renormalized as the pairing interaction is continuously tuned from a weak to a strong coupling regime. The unitary (crossover) regime, that lies intermediate to the BCS and BEC phases, described by a dimensionless parameter $1/k_{F}a$, where $-1\le1/k_{F}a\le1$ denotes the region of crossover, shows a monotonic increase of the pairing gap across the crossover, whereas the condensate fraction data is distinct with a non-monotonic behavior. The downturn in the latter result occurs at the crossover regime with a gradual depletion on the BEC side. A non-monotonic feature in the condensate fraction data has been noted earlier, in clean systems. Motivated by this result, we discuss the stability of a disordered fermionic superfluid in the crossover regime. [Preview Abstract] |
Wednesday, June 6, 2012 12:06PM - 12:18PM |
H2.00009: Matter-wave dynamics in a periodically pulsed disordered potential Bryce Gadway, Jeremy Reeves, Ludwig Krinner, Dominik Schneble We have experimentally studied the dynamical response of weakly-interacting atomic matter waves to a periodically pulsed, disordered optical lattice potential consisting of two overlapping standing-waves of incommensurate spatial periodicity. For periodic driving with a single-lattice potential, we observe behavior consistent with the kicked-rotor model, namely delocalization in momentum space at Talbot resonances as opposed to dynamic localization otherwise. However, adding the second lattice potential can greatly modify these two effects, which rely on constructive and destructive interference, respectively. In particular, we find that disorder leads to an inversion of the behavior in each case. The added incommensurate lattice destroys localization when the driving is off-resonant and suppresses delocalization for a resonant drive. [Preview Abstract] |
Wednesday, June 6, 2012 12:18PM - 12:30PM |
H2.00010: Free-space, multimode spatial self-organization of cold, thermal atoms Bonnie L. Schmittberger, Joel A. Greenberg, Daniel J. Gauthier The collective behavior of atoms upon interaction with light has been a topic of increasing interest since it was shown to lead to novel phase transitions. In order to induce a spontaneously-emergent lattice structure, cold atoms are typically placed in a cavity, which provides a sufficiently strong light-matter interaction. While many experiments have employed single-mode cavities, the use of multimode cavities would explore a new regime with the potential to study phenomena such as dislocations and topological defects. However, multimode cavities present certain technical challenges, and a strongly-interacting multimode system existing in free space is desirable. We create such a system by trapping cold, thermal atoms in a highly anisotropic MOT. When we shine counterpropagating beams along the long axis of our trap, we observe a superradiant phase transition from a homogeneous array of atoms to one that is spatially organized. We are able to infer information about this spatial self-organization by observing the superradiant light that is emitted in the form of transverse optical patterns. We find that the patterns spontaneously hop between spatial modes during single realizations of the experiment, and we study the effects of quantum fluctuations on the atomic organization. [Preview Abstract] |
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