Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 67, Number 7
Monday–Friday, May 30–June 3 2022; Orlando, Florida
Session H08: BoseEinstein Condensates IIRecordings Available

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Chair: Subhadeep Gupta, University of Washington Room: Salon 7/8 
Wednesday, June 1, 2022 8:00AM  8:12AM 
H08.00001: Fluctuations in imploding BoseEinstein condensates Eli J Halperin, Michael J Van de Graaff, John L Bohn, Jun Ye, Eric A Cornell Quantum and thermal effects play important roles in the fluctuations of ultracold Bose gasses, yet the fluctuations remain difficult to probe experimentally in 3D bulk systems. We report on a joint experimentaltheoretical effort which seeks to amplify these fluctuations via a quench from positive to negative scattering length. Following such a quench, initial fluctuations in the gas, whether seeded by a lattice potential, thermal fluctuations, or quantum fluctuations, are amplified on a timescale which is fast compared to the collapse of the cloud. These can be compared to a variety of theoretical models, which predict the static structure factor as a function of time and momentum in the collapsing gas. 
Wednesday, June 1, 2022 8:12AM  8:24AM 
H08.00002: Decoherence of MatterWave Breathers Yi Jin, Sehyun Park, Ricardo Espinoza, Randall G Hulet, Maxim Olshanii Solitons are nondispersive wave packets which arise as solutions to the 1D nonlinear Schrodinger equation (NLSE). Higherorder solitons, known as breathers, can be formed from fundamental solitons by a specific interaction quench. An nsoliton breather is composed of constituent fundamental solitons with mass ratios 1:3:…:2n1, and are formed when the attractive interactions are quenched by a factor of n^{2}, where n is an integer^{1}. A breather’s density profile oscillates in time at a frequency given by the chemical potential difference of its constituent solitons. Breathers are exactly integrable solutions to the NLSE in the meanfield (MF) limit. However, quantum manybody theory predicts that quantum fluctuations break integrability and can induce breather dissociation^{2} or relaxation resulting in loss of coherence^{3}. Using an interaction quench factor of 4 controlled through a magnetic Feshbach resonance, we experimentally produce secondorder breathers from a BoseEinstein condensate of ^{7}Li atoms in a quasi1D harmonic potential formed from a focused laser beam. We observe decoherence and dissociation of secondorder breathers, but the rate of these processes is inconsistent with beyond MF effects. 
Wednesday, June 1, 2022 8:24AM  8:36AM 
H08.00003: BoseEinstein Condensates near TwoDimensional Dirac Quantum Matter Valeri N Kotov, Adrian G Del Maestro We show that the presence of twodimensional (2D) Dirac materials, such as Graphene, can significantly affect quantum atomic phenomena that have traditionally served as probes of the fundamental van der Waals (VDW) / Casimir interaction. Attractive VDW potential tails between atoms and 2D materials are very strongly dependent on material characteristics (such as band structure, doping level, etc). We analyze theoretically manifestations of such 2D effects for atoms forming a confined BoseEinstein condensate (BEC) placed near 2D materials, which in turn makes the BEC frequency sensitive to the material presence. We find that relatively small 2D material changes (either by external factors such as strain or doping, or by using gapped 2D materials instead of graphene) can have profound effect on the trapping frequency of an atomic BEC condensate. In addition to atoms interacting with graphene in various configurations we have analyzed the 2D family of semiconducting dichalcogenides. These phenomena make 2D quantum materials an attractive platform for studies of manybody physics involving atoms near solid state environments. 
Wednesday, June 1, 2022 8:36AM  8:48AM 
H08.00004: Observation of bosonic stimulation in light scattering YuKun Lu, Yair Margalit, Wolfgang Ketterle For bosons, the transition rate into an already occupied quantum state is enhanced by its occupation number: the effect of bosonic stimulation. Bosonic enhancement of light scattering has been predicted more than 30 years ago but not observed before. Here we theoretically investigate and experimentally demonstrate this effect in an ultracold Bose gas. We show that the bosonic enhancement factor for a harmonically trapped gas is bounded by a universal constant ζ(2)/ζ(3) above the phase transition to a BoseEinstein condensate (BEC), and depends linearly on the BEC fraction just below the phase transition. Bosonically enhanced light scattering is observed and characterized above and below the phase transition, and the correction due to interaction is discussed. For a multilevel system, bosonic enhancement is reduced because bosonic stimulation occurs only for Rayleigh scattering, but not for Raman scattering. 
Wednesday, June 1, 2022 8:48AM  9:00AM 
H08.00005: Dynamics of dense twocomponent soliton trains in an elongated BoseEinstein condensate Sean Mossman, Garyfallia Katsimiga, Simeon I Mistakidis, Alejandro Romero Ros, Panagiotis Kevrekidis, Peter W Engels Solitons are a hallmark of nonlinear dynamics in BoseEinstein condensates. While the dynamics of individual solitons and of small clusters have been extensively studied, our experiments are now reaching the regime of dense trains of interacting solitons. We employ a phase winding technique to prepare regular arrays of darkbright solitons which exhibit surprisingly rich meanfield dynamics over the relatively long lifetime of these configurations. These dynamics are observed in real space then characterized through Fourier methods. The time evolution of spectral features is then compared against detailed numerical simulations. Understanding the dynamics of these structured quantum fluids has applications in benchmarking theoretical models for quantum hydrodynamics simulations and can provide an alternative viewpoint on the physics of supersolids. 
Wednesday, June 1, 2022 9:00AM  9:12AM 
H08.00006: From a polaron into a cluster: the fate of an impurity in a Bose Einstein condensate Arthur Christianen, J. Ignacio Cirac, Richard Schmidt Ultracold atomic gases can be used to simulate phenomena from condensed matter physics, such as the formation of polaron quasiparticles. However, at strong coupling a Bose polaron formed by an impurity atom in a Bose Einstein condensate (BEC) displays fascinating behavior quite distinct from the common condensed matter scenario. This is due to the possibility of bound state formation and the Efimov effect, which leads to attractive impuritymediated interactions between the bosons from the BEC. In particular, the intricate competition between this impuritymediated attraction and the intrinsic interboson repulsion plays an important role. In our work [1] we fully incorporate both of these processes and compare different variational methods to form a complete theoretical picture of the strong coupling Bose polaron. We find two parameter regimes with qualitatively different behavior. For light impurities and weak repulsion, the impuritymediated interactions dominate and we find a polaronic instability [2,3] due to the formation of large Efimov clusters. For strong repulsion or heavier impurities, we find that the formation of large clusters and the polaronic instability are prevented, and that there is a smooth crossover into a small cluster or molecule instead. 
Wednesday, June 1, 2022 9:12AM  9:24AM 
H08.00007: Engineering of Feshbach Resonances by a Floquet Drive Axel Pelster, Christoph Dauer, Sebastian Eggert Feshbach resonances are a common tool in order to control the scattering length in ultracold quantum gases [1]. In this talk we discuss how timeperiodic driving enables to induce novel resonances that are fully controllable by the parameters of the drive [2,3]. A theory allowing a deeper understanding of these driving induced resonances within the Floquet picture is given. Our method is capable of describing resonance positions and widths for general interparticle potentials. We demonstrate our results on an experimentally relevant example. 
Wednesday, June 1, 2022 9:24AM  9:36AM 
H08.00008: Light shift induced behaviors observed in momentumspace quantum walks Jerry H Clark, Nikolai Bolik, Caspar Groiseau, Alexander Gresch, Siamak Dadras, Gil Summy, Yingmei Liu, Sandro Wimberger Quantum walks (QWs) have seen many advances both experimentally and theoretically over the last decade with many proposed applications. Recently, a QW was experimentally realized utilizing a BoseEinstein Condensate (BEC) in momentum space. This QW was observed to be stable up to fifteen steps and exhibited behavior that agreed generally well with theoretical predictions. However, the QW also showed interesting behavior within the momentum distribution that wasn’t adequately explained by the theory. We propose a new theoretical model to offer an explanation based upon the parameters within the conducted experiments. This model also predicts that the discrepancy is dependent upon the initial momentum states used in creating the QW. 
Wednesday, June 1, 2022 9:36AM  9:48AM 
H08.00009: Continuouslytrapped atom interferometry in magic FloquetBloch bands Ethan Q Simmons, Hector Mas, Roshan Sajjad, Jeremy Tanlimco, Eber NolascoMartinez, David M Weld The performance of continuouslytrapped atom interferometers is limited by fluctuations in the trapping potential which induce positiondependent phase shifts. In analogy with magic wavelength optical traps, we numerically demonstrate the existence and experimental accessibility of "magic" drivetunable FloquetBloch band structures, in which an interferometric loop is insensitive to amplitude fluctuations in the trapping potential. We quantify the robustness of magic bands against trap fluctuations using both numerical solution of the timedependent Schrodinger equation and quasistatic calculations in an effective FloquetBloch band structure, and discuss prospects for the experimental realization of a magic continuouslytrapped atom interferometer. 
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