Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E05: Atomic Bose-Einstein CondensatesLive
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Chair: Cass Sackett, Virginia |
Tuesday, June 1, 2021 2:00PM - 2:12PM Live |
E05.00001: Effect of atomic interactions on tunneling time measurements David C Spierings, Joseph McGowan IV, Nick Mantella, Aephraim M Steinberg A Larmor clock uses the spin degree of freedom of tunneling particles to time the duration of the interaction between the particles and the barrier. It is well known that in the absence of inter-particle interactions, a Larmor clock measures the 'dwell time' (i.e. the expectation value of a projector onto the barrier region) of the wavepacket conditioned on transmission or reflection. Recently we observed that Larmor times for weakly interacting ultra-cold atoms tunneling through an optical barrier show good agreement with theory for conditional dwell times given by weak values. For these transmitted particles, atomic interactions do not significantly disturb the measurement of time but simply modify the momentum distribution of the incident wavepacket prior to collision with the barrier. For the reflected particles, however, the disturbance caused by atomic interactions is much more serious. We observe evidence of negative dwell times for a portion of the reflected wavepacket, perhaps indicative of interference between particles reflected from the barrier and those reflected from the wavepacket itself. Here, we discuss the implications for measurements of time in experiments on barrier penetration. |
Tuesday, June 1, 2021 2:12PM - 2:24PM Live |
E05.00002: Observation of pairs of atoms with opposite momenta in the quantum depletion of an interacting Bose gas Antoine Ténart, Gaétan Hercé, Jan-Philipp Bureik, Alexandre Dareau, David Clément Quantum fluctuations play a central role in the properties of quantum matter. In non-interacting ensembles, they manifest as fluctuations of non-commuting observables, quantified by Heisenberg inequalities. In the presence of interactions, additional quantum fluctuations appear, from which many-body correlations and entanglement originate. In the context of many-body physics, the Bogoliubov theory provides us with an illuminating microscopic picture of how this occurs for weakly-interacting bosons, with the appearance of the quantum depletion formed by pairs of bosons with opposite momenta. This conceptually simple example yet lacks experimental confirmation. Exploiting the single particle resolution of our metastable Helium detector, we report the direct observation of pairs of atoms with opposite momenta in the depletion of an equilibrium interacting Bose gas. We show that the pair correlation signal rapidly drops as temperature rises, as expected for the quantum depletion. A quantitative study of the atom-atom correlations, both at opposite and close-by momenta, allows us to fully characterise the quantum correlations in the interacting Bose gas. Our results demonstrate how an equilibrium many-body quantum state acquires specific correlations - those of two-mode squeezed states here - as a result of the interplay between quantum fluctuations and interactions. In addition, the measured amplitudes of the correlation signals reveal sub-poissonian number differences between modes at opposite momenta, an important step towards characterising entanglement in equilibrium many-body quantum states. |
Tuesday, June 1, 2021 2:24PM - 2:36PM Live |
E05.00003: Inversion of coherent backscattering with interacting Bose-Einstein condensates in two-dimensional disorder : a Truncated Wigner approach Renaud Chrétien, Peter Schlagheck We theoretically study the propagation of an interacting Bose-Einstein condensate in a two-dimensional disorder potential, following the principle of an atom laser. The constructive interference between time-reversed scattering paths gives rise to coherent backscattering, which may be observed under the form of a sharp cone in the disorder-averaged angular backscattered current. As is found by the numerical integration of the Gross-Pitaevskii equation, this coherent backscattering cone is inversed when a non-vanishing interaction strength is present, indicating a crossover from constructive to destructive interferences. Numerical simulations based on the Truncated Wigner method allow one to go beyond the mean-field approach and show that dephasing renders this signature of antilocalisation hidden behind a structureless and dominant incoherent contribution as the interaction strength is increased and the injected density decreased, in a regime of parameters far away from the mean-field limit. However, despite a partial dephasing, we observe that this weak antilocalisation scenario prevails for finite interaction strengths, opening the way for an experimental observation with 87Rb atoms. |
Tuesday, June 1, 2021 2:36PM - 2:48PM Live |
E05.00004: Vortex states within expanding Bose-Einstein Condensates Holly Alice Jess Middleton-Spencer, Carlo F Barenghi, Nick Parker, Luca Galantucci Time of flight imaging is an important technique to visualize atomic Bose-Einstein condensates. As the condensate cloud is released from its confinement, a plethora of phenomena can be observed, for example, a cigar shape condensate will expand and invert its aspect ratio – a signature well established in the literature. It has, however, been observed that a turbulent condensate does not undergo this inversion, and thus a self-similar expansion has been described as a tell-tale signature of turbulence within the condensate. |
Tuesday, June 1, 2021 2:48PM - 3:00PM Live |
E05.00005: Variational Adiabatic Hyperspherical Treatment of Bose-Einstein Condensates Hyunwoo Lee, Chris H Greene Novel tools are developed for understanding the fundamental properties of few and many bosons with low-energy s-wave interactions, combining the variational principle and the adiabatic hyperspherical formalism. An ansatz wave function [1], constructed out of independent-particle orbitals in relation to the Gross-Pitaevskii equation, has been shown to improve upon a previous method [2] in calculating the ground-state properties of the condensate, including the monopole excitation frequencies. Interestingly, systematic differences from Bogoliubov theory emerge in those computed frequencies. For attractive condensates, the single-orbital ansatz is insufficient for accurately computing the barrier protecting the metastable system from macroscopic collapse; an inclusion of many-body correlation using multiple orbitals is necessary to reach approximate agreement with mean-field methods in predicting the critical atom number where collapse occurs. Alternative ideas, involving functions of interparticle distances symmetrized in either the Jastrow or Faddeev form, are also being explored to describe several bosons at unitarity. |
Tuesday, June 1, 2021 3:00PM - 3:12PM Live |
E05.00006: Diffractive focusing of a uniform Bose-Einstein condensate Patrick B Boegel, Matthias Meister, Jan-Niclas Siemß, Naceur Gaaloul, Maxim Efremov, Wolfgang P Schleich The standard way to control the position and the strength of maximal focusing of a matter-wave is to use a lens which imprints a position-dependent phase on the initial wave. However, quantum mechanics allows focusing even without a lens [1,2], based on diffractive focusing, where the initial wave function is a real-valued one with a non-Gaussian shape. Hence, the problem of optimal focusing translates into finding an appropriate initial wave function [3]. |
Tuesday, June 1, 2021 3:12PM - 3:24PM Live |
E05.00007: Inflationary dynamics and particle production in a toroidal Bose-Einstein condensate Anshuman Bhardwaj
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Tuesday, June 1, 2021 3:24PM - 3:36PM Live |
E05.00008: Geometrizing quantum dynamics of Bose-Einstein condensates Changyuan Lyu, Chenwei Lv, Qi Zhou We show that quantum dynamics of Bose-Einstein condensates in the weakly interacting regime can be geometrized by a Poincaré disk. Each point on such a disk represents a thermofield double state, the overlap between which equals the metric of this hyperbolic space. This approach leads to a unique geometric interpretation of stable and unstable modes as closed and open trajectories on the Poincaré disk, respectively. The resonant modes that follow geodesics naturally equate fundamental quantities including the time, the length, and the temperature. Our work suggests a new geometric framework to coherently control quantum systems and reverse their dynamics using SU(1,1) echoes. In the presence of perturbations breaking the SU(1,1) symmetry, SU(1,1) echoes deliver a new means to measure these perturbations such as the interactions between excited particles. |
Tuesday, June 1, 2021 3:36PM - 3:48PM On Demand |
E05.00009: Macroscopic Quantum Tunnelling of a Metastable Bose-Einstein Condensate Rui-Bin Liu, Shizhong Zhang We investigate the dynamics of a metastable Bose-Einstein condensate (BEC) tunnelling from a cubic-plus-quadratic well to open space. By applying the Gross-Pitaevskii equation and the WKB method, we compute the tunnelling rate of the BEC out of the quasi-bound well and obtain explicit expressions in terms of s-wave scattering length and chemical potential. We find that the increase of the repulsive interaction and chemical potential lead to an enhancement of the decay rate of condensate. Our analytical results fit very well with the recent experimental observation for the relation between tunnelling rate and chemical potential of a quasi-bound condensate. |
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