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 H08: Few-body Physics at Ultracold TemperaturesLive
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Sponsoring Units: GFB Chair: Jose D'Incao, JILA |
Wednesday, June 2, 2021 8:00AM - 8:12AM Live |
H08.00001: Observation of coherent oscillations in molecular association from ultra cold thermal gasץ Roy Elbaz, Yaakov Yudkin, Lev Khaykovich A coherently driven 2-level system is well known to exhibit Rabi oscillations as a function of excitation duration. But if we replace one of the levels with a continuum, these oscillations will be smeared out by decoherence. The latter example is realized in molecular association from ultra cold free atoms. |
Wednesday, June 2, 2021 8:12AM - 8:24AM Live |
H08.00002: Efimov Spectrum takes a Turn Yaakov Yudkin, Roy Elbaz, Lev Khaykovich The interaction strength-dependence of a molecule's binding energy discloses crucial information about the system's interaction potential. In general, a bound state features a plethora of bendings, turns and avoided crossings. Contrarily, universal few-body bound states are insensitive to short-range details of the potential, given that their wave function extends far beyond the characteristic interaction range. Here we use refined, recently proposed few-body spectroscopy [1] to create a coherent superposition of two such universal bound states: Feshbach dimers and Efimov trimers. In an interferometer-like experiment we measure the Efimov binding energy relative to that of the dimer in the theoretically controversial and experimentally demanding regime where the first excited trimer supposedly merges with the dimer-atom continuum. Our results show that the Efimov trimer does not live up to its universal promise [2]. Instead we identify three distinct regimes, only one of which is captured by a universal theory, albeit accounting for finite range effects. As the interaction strength is weakened, upon entering the second regime, the energy level takes a sudden turn towards the dimer-atom continuum. It then goes through an avoided crossing such that in the third regime the binding energy increases with decreasing interaction strength. These observations come as a surprise and can serve a guide for realistic multi-channel few-body theories. |
Wednesday, June 2, 2021 8:24AM - 8:36AM Live |
H08.00003: Three-body recombination in a single-component Fermi gas near a p-wave Feshbach resonance Shangguo Zhu, Zhenhua Yu, Shizhong Zhang We study the three-body recombination in a single-component Fermi gas near a p-wave Feshbach resonance. We use a simple zero-range model for the resonant p-wave interaction between the fermionic atoms. When the scattering volume v is large and positive, we calculate the rate of the three-body recombination into weakly bound dimers and find it to scale as v5/2R1/2, where R is the p-wave effective range. |
Wednesday, June 2, 2021 8:36AM - 8:48AM Live |
H08.00004: Crossover from few-to many-body physics: Breakdown of the Bose polaron due to Efimov physics Arthur Christianen, J. Ignacio Cirac, Richard Schmidt Simple few-body physics can give rise to interesting emergent many-body effects. One such emergent effect arising at small particle number is the Efimov effect [1], where three particles with pairwise interactions form a special type of Borromean three-body bound state due to cooperative binding. In our work we study which role the Efimov effect plays in many-body systems. To this end, we theoretically study the role of Efimov physics in the paradigmatic model of the Bose polaron [2], an impurity immersed in a BEC. We use a variational method based on Gaussian States in the reference frame of the impurity [3]. This Ansatz allows for an arbitrary number of bosonic excitations with pairwise interboson correlations and three-body correlations involving the impurity. We show that the formation of large Efimov-like bound states can lead to the breakdown of the polaron for light impurities. Our results can be probed in experiments with cold atom mixtures using currently available state-of-the-art techniques. |
Wednesday, June 2, 2021 8:48AM - 9:00AM Live |
H08.00005: Prethermal and Efimovian dynamics of the quenched unitary Bose gas Victor Colussi, Hadrien Kurkjian, Mathias Van Regemortel, Silvia Musolino, Jasper van de Kraats, Michiel Wouters, Servaas Kokkelmans We study the quench of a degenerate ultracold Bose gas to the unitary regime, using a cumulant theory able to capture both higher-order interactions which break integrability and non-perturbative few-body physics including the Efimov effect. After an initial period of rapid quantum depletion, a universal prethermal stage is established, characterized by an emergent Bogoliubov dispersion law and an associated universal sound speed. Integrability is then broken by higher-order interactions, which leads to a momentum-dependent departure form the prethermal stage. We also find signatures of the Efimov effect in the many-body dynamics and make a precise identification between the observed beating phenomenon of short-distance three-body correlations and the binding energy of an Efimov trimer. |
Wednesday, June 2, 2021 9:00AM - 9:12AM Live |
H08.00006: Universal behaviour of excited three-body bound states in 1D Lucas Happ, Maxim Efremov We study a three-body system confined to one spatial dimension, consisting of two identical, non-interacting particles and a third, different particle interacting with each of the two identical ones. In [1] we have found universality in such systems, provided the heavy-light interaction is tuned to the ground-state resonance. We extend this study to the case of the heavy-light interaction being tuned such that an excited-state of arbitrary symmetry is on resonance, hence allowing for deeply bound states in the three-body system. Within the framework of the Faddeev equations we find universal behaviour of the associated three-body bound states [2]. Moreover, we analyze the influence of those deeply bound states on the three-body universality. In this talk we present numerical and analytical results for the energy spectrum and the corresonding three-body wave functions. |
Wednesday, June 2, 2021 9:12AM - 9:24AM Live |
H08.00007: Few-body correlations in two-dimensional Bose and Fermi ultracold mixtures George Bougas, Simeon Mistakidis, Panagiotis Giannakeas, Peter Schmelcher Few-body correlations emerging in two-dimensional harmonically trapped mixtures, consisting either of two identical bosons or fermions and another distinguishable particle, for arbitrary mass ratios are investigated. In particular, the properties of the relevant two- and three-body contacts are discussed for varying interspecies interaction and corresponding analytical insights are provided within the hyperspherical formalism. It is exemplified that the presence of the trap leads to the formation of additional atom-dimer and trap states. Remarkably, the two-body contact of the atom-dimer and trap states features an analytically predicted upper bound depending solely on the two-dimensional scattering length. Such a correlation bound is absent in the three-body contact. Interestingly, by tuning the scattering length the contacts oscillate as the atom-dimer and trap states change character, a behavior captured in the energy spectra of the system. For thermal gases the oscillation amplitude decreases with increasing temperature, resulting in turn to the suppression of the involved two- and three-body correlations. |
Wednesday, June 2, 2021 9:24AM - 9:36AM Live |
H08.00008: Efimov-like states and quantum funneling effects on synthetic hyperbolic surfaces Ren Zhang, Chenwei Lv, Yangqian Yan, Qi Zhou Engineering lattice models with tailored inter-site tunnelings and onsite energies could synthesize essentially arbitrary Riemannian surfaces with highly tunable local curvatures. Here, we point out that discrete synthetic Poincar\'e half-planes and Poincar\'e disks, which are created by lattices in flat planes, support infinitely degenerate eigenstates for any nonzero eigenenergies. Such Efimov-like states exhibit a discrete scaling symmetry and imply an unprecedented apparatus for studying quantum anomaly using hyperbolic surfaces. |
Wednesday, June 2, 2021 9:36AM - 9:48AM Live |
H08.00009: Searching for signatures of Efimov physics in universal many-body dynamics Jiri Etrych, Gevorg Martirosyan, Jake A Glidden, Lena Dogra, Christoph Eigen, Zoran Hadzibabic According to the universality hypothesis, in a degenerate unitary gas the dynamics depend solely on the gas density as the s-wave scattering length diverges and drops out of the problem. However, for Bose gases Efimov physics introduces additional lengthscales and remains a part of the problem. Here we explore the dynamics of 39K Bose gases quenched to unitarity, initially preparing degenerate homogeneous clouds of varying density in different internal spin states and at different Feshbach resonances, the positions of which we calibrate using high-precision binding energy measurements. We rapidly quench the magnetic field to the unitary regime, wait for a variable hold time, before returning to weak interactions and observing the samples. By comparing the different spin states with varying Efimov parameters we explore the quasi-equilibrium prethermal state that is reached at intermediate times, and study the loss, energy, and molecular correlation dynamics as the cloud decays and heats. |
Wednesday, June 2, 2021 9:48AM - 10:00AM Live |
H08.00010: Analyzing quantum chaos in three-body systems with machine learning David Huber, Oleksandr Marchukov, Hans W Hammer, Artem Volosniev The relative motion of three impenetrable particles on a ring, in our case two identical fermions and one impurity, is isomorphic to a triangular quantum billiard. Depending on the ratio of the impurity and fermion masses, the billiards can be integrable or non-integrable (also referred to as chaotic). We use machine learning tools to analyze properties of probability distributions of individual quantum states. We find that convolutional neural networks can correctly classify integrable and non-integrable states. The decisive features of the wave functions are the normalization and a large number of zero elements, corresponding to the existence of a nodal line. The network achieves high accuracies, suggesting that machine learning tools can be used to analyze and classify the morphology of probability densities obtained in theory and experiment. |
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