Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J27: Strongly Interacting Quantum Gases ILive

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Sponsoring Units: DAMOP Chair: Qi Zhou, Purdue Univ 
Tuesday, March 16, 2021 3:00PM  3:12PM Live 
J27.00001: Z_{2} parton phases in the mixeddimensional tJ_{z} model Lode Pollet, Fabian Grusdt We study the interplay of spin and charge degrees of freedom in a doped Ising antiferromagnet, where the motion of charges is restricted to one dimension. The phase diagram of this mixeddimensional t−J_{z} model can be understood in terms of spinless chargons coupled to a Z_{2} lattice gauge field. The antiferromagnetic couplings give rise to interactions between Z_{2} electric field lines which, in turn, lead to a robust stripe phase at low temperatures. At higher temperatures, a confined mesongas phase is found for low doping whereas at higher doping values, a robust deconfined chargongas phase is seen which features hidden antiferromagnetic order. We confirm these phases in quantum Monte Carlo simulations. Our model can be implemented and its phases detected with existing technology in ultracold atom experiments. The critical temperature for stripe formation with a sufficiently high hole concentration is around the spinexchange energy J_{z}, i.e., well within reach of current experiments. 
Tuesday, March 16, 2021 3:12PM  3:24PM Live 
J27.00002: Quantum Statistics of a ShellShaped BoseEinstein Condensate Andrea Tononi, Axel Pelster, Luca Salasnich The recent development of NASA's Cold Atom Laboratory, a spacebased facility for ultracold atoms experiments, allows the routine production of BoseEinstein condensates in microgravity. The ongoing investigations are focusing on shellshaped geometries, in which the atoms are confined on a thin ellipsoidal surface with radio frequencyinduced adiabatic potentials. We analyze the quantum statistical properties of spherical and ellipsoidal shells, focusing on the phenomena of BoseEinstein condensation and superfluidity. Moreover, we discuss the physics of topological excitations on a spherical superfluid, which drive the BerezinskiiKosterlitzThouless transition, and their interplay with the curvature of the hosting surface. Our results are a reliable benchmark for the current experimental investigations. 
Tuesday, March 16, 2021 3:24PM  3:36PM Live 
J27.00003: Observation of spin and charge excitations in a strongly interacting 1D Fermi Gas Ruwan Senaratne, Danyel CavazosCavazos, YaTing Chang, Randall G Hulet One of the key predictions of the TomonagaLuttinger liquid (TLL) theory of interacting fermions in 1D is the decoupling of the spin and charge degrees of freedom. We measure the difference in the propagation speeds for the density and the spin modes in a TLL as a function of the strength of repulsive interactions. A pseudospin1/2 system is realized with the lowest and thirdtolowest, 1>3>, hyperfine sublevels of ^{6}Li. The atoms are loaded into a 2D optical lattice, which creates an array of quasi1D tubes. We tune the interspecies interactions via a magnetic Feshbach resonance and use Bragg spectroscopy with k = 0.2 k_{F} to measure the lowenergy excitation spectra for both modes. Using the narrowlinewidth 2S3P transition in combination with the chosen state mixture minimizes spontaneous emission while exciting the spinmode with Bragg beams tuned between the resonance frequencies of the two states. We compare the measured dynamical structure factor with the TLL theory, thus realizing the first observation of spincharge separation with tunable interaction strength. 
Tuesday, March 16, 2021 3:36PM  3:48PM Live 
J27.00004: Collisional loss of onedimensional fermions near a pwave Feshbach resonance YaTing Chang, Ruwan Senaratne, Danyel CavazosCavazos, Randall G Hulet Recent interest in faulttolerant quantum computing has focused attention on nonabelian anyons [1] which may be created in 1D pwave superconductors, or, as discussed here, in an atomic Fermi gas with pwave interactions. Severe atom losses, however, due to threebody recombination near the pwave Feshbach resonance (FR) has, thus far, prevented the realization of pwave superfluids in ultracold atomic gases. Motivated by recent theoretical work predicting the suppression of losses in quasi1D [2], we measured the collisional loss of a spinpolarized Fermi gas near a pwave FR using ^{6}Li atoms confined to a 2D optical lattice [3]. We observe little dependence of the peak threebody loss rate on the confinement strength. We find a possible suppression, however, by analzing the data using a cascade model in which Feshbach dimers are first formed, then are lost to the creation of deeplybound molecules by atomdimer collisions. We will present our results and discuss the implications of these measurements for observing pwave pairing in quasi1D. 
Tuesday, March 16, 2021 3:48PM  4:00PM Live 
J27.00005: The BoseGlass Phase in MeanField Quasicrystalline Systems Dean Johnstone, Callum Duncan, Patrik Öhberg We study the ground state phases of the BoseHubbard model with disordered potentials for quasicrystalline systems, with a focus on the BoseGlass phase. Generally speaking, disorder can lead to the formation of a BoseGlass, which is characterised by the lack of global phase coherence across the lattice. Here, we look at two models; the interacting 2D AubryAndre model and disordered quasicrystalline vertex models. Unlike typical disorder in homogeneous, periodic systems, quasicrystalline models possess selfsimilarity. This leads to a fascinating interplay between correlated, quasiperiodic order and uncorrelated, random disorder. In this work, we use a meanfield percolation analysis of superfluid clusters to map out the critical points and phase regions of these disordered systems. When the longrange order is separate to the random disorder, as is the case for the disordered vertex models, then the physics reflects that of periodic lattices with disorder. However, we find that longrange order present in the disorder term of the 2D AubryAndre model can result in some peculiarities to the physics of the BoseGlass. This includes stabilisation from weak disorder lines and intricate, ordered structures of the phase itself that may provide fruitful areas of future study. 
Tuesday, March 16, 2021 4:00PM  4:12PM Live 
J27.00006: Preparation of the 1/2Laughlin state with atoms in a rotating trap Bárbara Andrade dos Santos, Valentin Kasper, Maciej A Lewenstein, Christof Weitenberg, Tobias Grass Ultracold atomic systems belong to the most promising platforms to study elusive strongly correlated states such as the fractional quantum Hall state. In our study, we simulate four bosonic atoms in a quasitwodimensional rotating trap, which will act as a bosonic analog of electrons in a magnetic field. For rotation frequencies close to the inplane trapping frequency, the ground state is predicted to be a bosonic Laughlin state at half filling. Here, we study the adiabatic preparation of the Laughlin state by varying the rotation frequency and the ellipticity of the trapping potential. By using tailored ramping speeds for the rotation frequency and ellipticity, we significantly improve the preparation time of the Laughlin state with high fidelity. Finally, this improvement of the adiabatic protocol allows to prepare the Laughlin state with current experimental technology. 
Tuesday, March 16, 2021 4:12PM  4:24PM Live 
J27.00007: Bosonic continuum theory of onedimensional lattice anyons Martin Bonkhoff, Kevin Jägering, Sebastian Eggert, Axel Pelster, Michael Thorwart, Thore Posske Recent experimental advances in ultracold atomic gases have opened a route towards onedimensional abelian anyons via bosons with an occupationdependent hopping. Thereby, tunable twoparticle interactions take over the role of intricate topological quantum mechanical constraints. Yet, this method crucially depends on the existence of a discrete lattice. A corresponding anyonic continuum theory that obeys the necessary periodicity in the anyonic phase angle is unknown. In this talk, we provide the continuum limit of onedimensional lattice anyons and its representation by onedimensional bosons. The theory maintains the periodicity in the anyonic phase and includes current density as well as threebody interactions. In the limit of a small anyonic phase, the integrable Kundu model is recovered. Here, our analysis provides a physical explanation of controversially discussed divergences. The results show how onedimensional anyons in the continuum are experimentally accessible in purely bosonic systems. 
Tuesday, March 16, 2021 4:24PM  4:36PM 
J27.00008: Observation of a Smooth PolaronMolecule Transition in a Degenerate Fermi Gas Gal Ness, Constantine Shkedrov, Yanay Florshaim, Oriana Diessel, Jonas von Milczewski, Richard Schmidt, Yoav Sagi Understanding the behavior of a spin impurity stronglyinteracting with a Fermi sea is a longstanding challenge in manybody physics. For shortrange interactions and zero temperature, most theories predict a firstorder phase transition between a polaronic ground state and a molecular one. We study this question with an ultracold Fermi gas, utilizing a novel highsensitivity Raman spectroscopy probing technique that allows us to isolate the quasiparticle contribution [1]. As the interaction strength is increased, we observe a continuous variation of all observables, in particular a smooth reduction of the quasiparticle weight as it goes to zero beyond the transition point. Our observation is in good agreement with a theoretical model where polaron and molecule quasiparticle states are thermally occupied according to their quantum statistics. At the experimental conditions, polaron states are hence populated even at interactions where the molecule is the ground state and vice versa. The emerging physical picture is thus that of a smooth transition between polarons and molecules and a coexistence of both in the region around the expected transition. 
Tuesday, March 16, 2021 4:36PM  4:48PM Live 
J27.00009: New soluble model of interacting fermions in onedimension Seth Grable, Noah Kamm, Harsh Mathur

Tuesday, March 16, 2021 4:48PM  5:00PM Live 
J27.00010: Mesoscopic spin transport between strongly interacting Fermi gases Yuta Sekino, Hiroyuki Tajima, Shun Uchino We investigate mesoscopic spin transport for strongly interacting Fermi gases through a quantum point contact [1]. Under the situation in which spin polarizations in the left and right reservoirs are the same in magnitude but opposite in sign, we calculate the contribution of quasiparticles to the spin current by means of the linear response theory and manybody Tmatrix approximation. For a small spinbias regime, the current in the vicinity of the superfluid transition temperature is strongly suppressed due to the formation of pseudogaps. For a large spinbias regime where the gases become highly polarized, on the other hand, the current is affected by the enhancement of a minority density of states due to Fermi polarons. 
Tuesday, March 16, 2021 5:00PM  5:12PM 
J27.00011: Universal Aspects of a Strongly Interacting Impurity in a Dilute Bose Condensate Pietro Massignan, Nikolay Yegovtsev, Victor Gurarie We study the properties of an impurity immersed in a weakly interacting Bose gas, i.e., of a Bose polaron. In the perturbativelytractable limit of weak impurityboson interactions many of its properties are known to depend only on the scattering length. Here we demonstrate that for strong (unitary) impurityboson interactions all static quasiproperties of a Bose polaron in a dilute Bose gas, such as its energy, its residue, its Tan’s contact and the number of bosons trapped nearby the impurity, depend on the impurityboson potential via a single parameter. 
Tuesday, March 16, 2021 5:12PM  5:24PM Live 
J27.00012: Lightassisted ultracold chemical reactions between Rydberg atoms and polar molecules Vanessa Carolina Olaya Agudelo, Jesus Perez Rios, Felipe Herrera Ultracold scattering experiments with Rydberg atoms in dense neutral atomRydberg mixtures has led to the discovery of exotic bound longrange Rydberg molecules, with a ground state atom residing within the orbit of a Rydberg electron [2]. We now study the longrange interaction of Rydberg alkalimetal atoms with heteronuclear alkalimetal dimers in the regime of low molecular densities, such that the Rydbergdimer interaction is dominated by van der Waals forces. We compute accurate C_{6 }coefficients for a large set of atomic Rydberg states n^{2}L_{j } interacting with ground state molecules [3]. For the (5^{2}S_{1/2})^{87}RbKRb(J=0) collision pair, we predict large probabilities for forming longrange Rydbergmolecule bound states (trimers) with (n∼50)^{2}D atomic Rydberg character, in a twophoton photoassociation scheme. We discuss the feasibility of detecting RbKRb trimers in currently available atommolecule cotrapping experiments. 
Tuesday, March 16, 2021 5:24PM  5:36PM Live 
J27.00013: Quantum phases of Rydberg atoms in twodimensional arrays Rhine Samajdar, Wen Wei Ho, Hannes Pichler, Mikhail Lukin, Subir Sachdev We describe the zerotemperature phases of twodimensional arrays of neutral atoms, excited into Rydberg states and interacting via strong van der Waals interactions. Using the densitymatrix renormalization group algorithm, we map out detailed phase diagrams and obtain a rich variety of phases featuring complex density wave orderings, upon varying lattice spacing and laser detuning. While some of these phases result from the classical optimization of the van der Waals energy, we also find intrinsically quantumordered phases stabilized by quantum fluctuations. These phases are surrounded by novel quantum phase transitions, which we analyze by finitesize scaling numerics and Landau theories. Our work highlights Rydberg quantum simulators in higher dimensions as promising platforms to realize exotic manybody physics. We also discuss how Rydberg atom arrays can be a natural platform for probing topological phenomena based on appropriate lattice geometries and innate interactions, even without engineering specific gauge constraints. 
Tuesday, March 16, 2021 5:36PM  5:48PM Live 
J27.00014: Peierls/SuSchriefferHeeger polarons in two dimensions Chao Zhang, Nikolai Prokof'ev, Boris Svistunov Previous studies find that when the electronphonon coupling depends only on phonon momentum, the ground state properties feature a smooth crossover from weak to strong coupling. In the model with Peierls/SuSchriefferHeeger (PSSH) coupling, when the interaction vertex depends also on the electron momentum, a competingsectors transition between states with zero and nonzero momentum of the ground state has been found in onedimension. However, it remained unclear whether this transition is a generic property of models with the PSSH type of coupling, or it depends on the model details and dimensionality. We employ the Diagrammatic Monte Carlo method to study single polarons in two different twodimensional PSSH models. In one of them, we find that in both adiabatic and nonadiabatic regimes, the momentum of the ground state changes from zero to a finite value as a function of coupling strength because the dispersion curve features two competing minima. At the transition point the ground state effective mass reaches a maximum and starts decreasing when the coupling is increased beyond the critical value. 
Tuesday, March 16, 2021 5:48PM  6:00PM Live 
J27.00015: Dissipative Topological Phase Transition with Strong SystemEnvironment Coupling Wei Nie, Mauro Antezza, Yuxi Liu, Franco Nori Protection of topological phases in environments is essential for topological quantum technologies. In this work, we study how a topological system interplays with its environment. We find that the topological phase survives the environment for an emergent translational symmetry in the environmentinduced interaction. The strong systemenvironment coupling leads to a transition between the topological and nontopological phases. This phase transition not only presents an intrinsic relation between environmentinduced decay and spectrum width of the topological system, but also signals a nontrivial change of dissipation of the edge states; namely, a dissipative topological phase transition. Near the critical point, edge states are protected against decoherence. Our work uncovers nontrivial topologies and protected edge states due to the interplay between system and environment in the strongcoupling regime. 
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