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 X09: ManyBody Dynamics in Trapped GasesRecordings Available

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Chair: Nir Navon, Yale Room: Salon 11/12 
Friday, June 3, 2022 8:00AM  8:12AM 
X09.00001: InteractionDriven Spin Rotations in a Twocomponent BEC Reflecting from a Barrier David C Spierings, Joseph McGowan IV, Nicholas Mantella, Joseph H Thywissen, Aephraim M Steinberg Reflection from a barrier perturbed by weak Raman coupling beams generates spin waves in a BEC of ^{87}Rb. Due to the coincidence of scattering lengths in ^{87}Rb, a BEC in a mixture of two hyperfine states behaves as a phasecoherent yet distinguishable twocomponent fluid. Reflection from the barrier creates a counterpropagating matter wave with spin partly transverse to the spin of the forwardgoing wave, initiating interactiondriven rotations. The observed spin rotations are welldescribed by meanfield simulations with equal inter and intraspin interaction strengths, demonstrating that the spin dynamics do not arise from nonequilibrium dynamics caused by spindependent interactions or immiscibility of the two components. Rather, the driving mechanism for spin rotations is the different interaction energy experienced by parallel versus antiparallel spins in different spatial modes, much in the same way the identical spin rotation effect is known to generate spin waves in noncondensed gases. We observe one oscillation of a spin wave for low Rabi frequencies and study the transition where spin rotations become independent of the external coupling and instead are dominated by the interactiondriven effects. 
Friday, June 3, 2022 8:12AM  8:24AM 
X09.00002: Vortexcore phase transition iin the polar phase of spin1 BoseEinstein condensates Hiromitsu Takeuchi Vortex core structure in the polar phase of spin1 BoseEinstein condensates is investigated theoretically. Singly quantized vortices are categorized by the local ordered state in the vortex core and three types of vortices are found as lowestenergy vortices, elliptic AFcore vortices, axisymmetric Fcore vortices, and Ncore vortices. These vortices are named after the local ordered state, ferromagnetic (F), antiferromagnetic (AF), brokenaxisymmetry (BA), and normal (N) states apart from the bulk polar (P) state. The Ncore vortex is a conventional vortex, in the core of which the superfluid order parameter vanishes. The other two types of vortices are stabilized when the quadratic Zeeman shift is below a critical value. The axisymmetric Fcore vortex is the lowestenergy vortex for ferromagnetic interaction, and it has an F core surrounded by a BA skin that forms a ferromagneticspin texture, as exemplified by the localized MerminHo texture. The elliptic AFcore vortex is stabilized for antiferromagnetic interaction; the vortex core has both nematicspin and ferromagnetic orders locally and is composed of the AFcore soliton spanned between two BA edges. The phase transition from the Ncore vortex to the other two vortices is continuous, whereas that between the AFcore and Fcore vortices is discontinuous. The critical point of the continuous transition is computed by the perturbation analysis of the Bogoliubov theory and the GinzburgLandau formalism describes the critical behavior. The influence of trapping potential on the core structure is also investigated. 
Friday, June 3, 2022 8:24AM  8:36AM 
X09.00003: Squeezed Ground States in a Spin1 BoseEinstein Condensate Lin Xin, Maryrose Barrios, Julia T Cohen, Michael S Chapman In this work, we generate spin squeezed ground states in an atomic spin1 BoseEinstein condensate tuned near the quantum critical point between the polar and ferromagnetic quantum phases of the interacting spin ensemble. In contrast to typical nonequilibrium methods for preparing atomic squeezed states by quenching through a quantum phase transition, squeezed ground states are timestationary and remain squeezed for the lifetime of the condensate. 
Friday, June 3, 2022 8:36AM  8:48AM 
X09.00004: Effects of the transverse direction on the manybody tunneling dynamics Anal Bhowmik, Sudip K Haldar, Ofir E Alon Tunneling in a manyparticle system appears as one of the novel implications of quantum physics. Here, we theoretically investigate the tunneling dynamics of a few intricate bosonic clouds in a twodimensional symmetric doublewell potential. We unravel how the inclusion of the transverse direction, orthogonal to the junction of the doublewell, can intervene in the tunneling dynamics of bosonic clouds by employing a wellknown manybody numerical method, the multiconfigurational timedependent Hartree for bosons (MCTDHB), which incorporates quantum correlations exhaustively. We analyze the tunneling dynamics by preparing the initial state of the bosonic clouds in the left well of the doublewell either as the ground, longitudinally or transversely excited, or a vortex state. We examine the detailed mechanism of the tunneling process by analyzing the evolution in time of the survival probability, depletion and fragmentation, and the manyparticle position, momentum, and angularmomentum expectation values and their variances. As a general rule, all objects lose coherence while tunneling through the barrier and the states which include transverse excitations do so faster. In particular for the later states, we show that even when the transverse direction is practically frozen, prominent manybody dynamics in a twodimensional bosonic Josephson junction occurs. 
Friday, June 3, 2022 8:48AM  9:00AM 
X09.00005: Short time dynamics after a wavefunction quench in 1D Bose gases Yuan Le, Yicheng Zhang, Neel Malvania, Marcos Rigol, David S Weiss Generalized hydrodynamics (GHD) has recently been shown to describe the dynamics in nearlyintegrable 1D Bose gases very well, even after strong quenches of the trap [1]. We now study these gases shortly after a wavefunction quench, in which the atoms are put into a superposition of multiple momentum states by an axial Bragg pulse. After the quench, the gases are out of local equilibrium with the local generalized Gibbs ensemble (GGE), so GHD dose not apply. We measure how the momentum distribution of the center peak evolves up to the point that the local GGE is satisfied. We perform numerical calculations and GHD in the infinite coupling limit, to identify when the GGE is satisfied in that case [2,1]. We then apply this understanding to extracting the local equilibration time constants for different densities and coupling strengths. These time constants are at the frontier of what can be theoretically calculated about nonequilibrium nearlyintegrable systems. 
Friday, June 3, 2022 9:00AM  9:12AM 
X09.00006: Anomalous localization in spin chains coupled to a nonlocal degree of freedom Saeed Rahmanian Koshkaki, Koki Chinzei, Michael Kolodrubetz It has recently been predicted that manybody localization survives the presence of coupling to a nonlocal degree of freedom, such as a cavity mode [PRL 122, 240402 (2019)]. Such a cavityQED system can host anomalous phases unique to nonequilibrium systems. Here we present recent results on anomalous localization in such setups. First, we show that for the right choice of nonlocal degree of freedom, an inverted mobility edge occurs, meaning that infinite temperature states are localized while low energy states are delocalized. Second, we show a similar model can be used for realizing time crystals in cavityQED systems and in the absence of drive, i.e., a timecrystalline phase in a static Hamiltonian. Finally, we study the stability of localization in the presence of nonzero but small photon loss. All the models presented are realizable on experimental AMO platforms. 
Friday, June 3, 2022 9:12AM  9:24AM 
X09.00007: Rotating Bose gas dynamically enters the lowest Landau level Vaibhav Sharma, Erich J Mueller Motivated by recent experiments, we model the dynamics of a condensed Bose gas in a rotating anisotropic trap. The equations of motion of neutral particles in a rotating frame are analogous to those of charged particles in a magnetic field. As the rotation rate is ramped from zero to the trapping frequency, the condensate stretches along one direction and is squeezed along another, becoming long and thin. When the trap anisotropy is slowly switched off on a particular timescale, the condensate is left in the lowest Landau level. We use a time dependent variational approach to quantify these dynamics and give intuitive arguments about the structure of the condensate wavefunction. This preparation of a lowest Landau level condensate can be an important first step in realizing bosonic analogs of quantum Hall states. 
Friday, June 3, 2022 9:24AM  9:36AM 
X09.00008: Interface properties and phase transitions in atomic Boson – Fermion mixtures Bishal Parajuli, ChihChun Chien We study the density profiles of atomic boson – fermion mixtures confined in one dimensional box potentials by modelling the system with manybody densitydensity interactions. A variety of configurations were found in the different parameter regime. Atomic mixtures can remain mixed, and phase separate in 3chunk or 2chunk structure depending on the bosonboson and the bosonfermion interaction strengths. Phase diagram for all the structures as a function of the interactions is mapped out. For the 2chunk structure, interface properties which describes the interaction between the separated bosons and fermions were analyzed. The width of the interface reveals information about interaction and other parameters. At the hard walls, the density profiles of bosons or fermions show the healing length of the corresponding system. And at the boson  fermion interface, the width depends on both kinetic and interaction energy which can be tuned by the atomic mass, bosonfermion interaction and their densities. 
Friday, June 3, 2022 9:36AM  9:48AM 
X09.00009: Rainbow Scars: From Area to Volume Law Christopher M Langlett, Julia S Wildeboer, Shenglong Xu, Thomas Iadecola, Alexey V Gorshkov, Zhicheng Yang Quantum manybody scars (QMBS) constitute a new quantum dynamical regime in which rare “scarred” eigenstates mediate weak ergodicity breaking. One open question is to understand the most general setting in which these states arise. In this work, we develop a generic construction that embeds a new class of QMBS, rainbow scars, into the spectrum of an arbitrary Hamiltonian. Unlike other examples of QMBS, rainbow scars display extensive bipartite entanglement entropy while retaining a simple entanglement structure. Specifically, the entanglement scaling is volumelaw for a random bipartition, while scaling for a finetuned bipartition is subextensive. When internal symmetries are present, the construction leads to multiple, and even towers of rainbow scars revealed through distinctive nonthermal dynamics. Remarkably, certain symmetries can lead rainbow scars to arise in translationinvariant models. To this end, we provide an experimental road map for realizing rainbow scar states in a Rydbergatom quantum simulator, leading to coherent oscillations distinct from the strictly subvolumelaw QMBS previously realized in the same system. 
Friday, June 3, 2022 9:48AM  10:00AM 
X09.00010: Eigenstate thermalization approaching for an atom interacting with fixed scatterers Vladimir Yurovsky Eigenstate thermalization is generally studied in manybody systems. It can be approached even if all but one particles have the infinite mass, as demonstrated here. Since n zerorange scatterers along the axis of a circular, transversely harmonic waveguide form a separable potential, millions of eigenstates are calculated using modest computational resources. On increase of n, the common characteristic of quantum chaos — the level spacing statistics — diverges from the Seba one [1] and at n=64 approaches the WignerDyson one for the Gaussian orthogonal ensemble (GOE), expected for complete chaos. When the energy spectrum degeneracy with no scatterers is eliminated by an axial vector potential, at n=16 the level statistics approaches the one for the Gaussian unitary ensemble, expected for complete quantum chaos with no Tinvariance. In this case, GOE takes place only for Pinvariant distribution of the scatterers, when the Hamiltonian is TPinvariant. Chaotic behavior is revealed also in the inverse participation ratio [1], which drops from 0.4 to 0.028 on increase of n from 4 to 32. Simultaneous 4time reduction of the eigenstate expectation value dispersion demonstrates the eigenstate thermalization approaching. 1.V. A. Yurovsky and M. Olshanii, PRL 106, 025303 (2011). 
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