Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
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: Z2 parton phases in the mixed-dimensional t-Jz 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 mixed-dimensional t−Jz model can be understood in terms of spin-less chargons coupled to a Z2 lattice gauge field. The antiferromagnetic couplings give rise to interactions between Z2 electric field lines which, in turn, lead to a robust stripe phase at low temperatures. At higher temperatures, a confined meson-gas phase is found for low doping whereas at higher doping values, a robust deconfined chargon-gas 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 spin-exchange energy Jz, i.e., well within reach of current experiments. |
Tuesday, March 16, 2021 3:12PM - 3:24PM Live |
J27.00002: Quantum Statistics of a Shell-Shaped Bose-Einstein Condensate Andrea Tononi, Axel Pelster, Luca Salasnich The recent development of NASA's Cold Atom Laboratory, a space-based facility for ultracold atoms experiments, allows the routine production of Bose-Einstein condensates in microgravity. The ongoing investigations are focusing on shell-shaped geometries, in which the atoms are confined on a thin ellipsoidal surface with radio frequency-induced adiabatic potentials. We analyze the quantum statistical properties of spherical and ellipsoidal shells, focusing on the phenomena of Bose-Einstein condensation and superfluidity. Moreover, we discuss the physics of topological excitations on a spherical superfluid, which drive the Berezinskii-Kosterlitz-Thouless 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 Cavazos-Cavazos, Ya-Ting Chang, Randall G Hulet One of the key predictions of the Tomonaga-Luttinger 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 pseudospin-1/2 system is realized with the lowest- and third-to-lowest, |1>-|3>, hyperfine sublevels of 6Li. The atoms are loaded into a 2D optical lattice, which creates an array of quasi-1D tubes. We tune the inter-species interactions via a magnetic Feshbach resonance and use Bragg spectroscopy with k = 0.2 kF to measure the low-energy excitation spectra for both modes. Using the narrow-linewidth 2S-3P transition in combination with the chosen state mixture minimizes spontaneous emission while exciting the spin-mode 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 spin-charge separation with tunable interaction strength. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J27.00004: Collisional loss of one-dimensional fermions near a p-wave Feshbach resonance Ya-Ting Chang, Ruwan Senaratne, Danyel Cavazos-Cavazos, Randall G Hulet Recent interest in fault-tolerant quantum computing has focused attention on non-abelian anyons [1] which may be created in 1D p-wave superconductors, or, as discussed here, in an atomic Fermi gas with p-wave interactions. Severe atom losses, however, due to three-body recombination near the p-wave Feshbach resonance (FR) has, thus far, prevented the realization of p-wave superfluids in ultracold atomic gases. Motivated by recent theoretical work predicting the suppression of losses in quasi-1D [2], we measured the collisional loss of a spin-polarized Fermi gas near a p-wave FR using 6Li atoms confined to a 2D optical lattice [3]. We observe little dependence of the peak three-body 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 deeply-bound molecules by atom-dimer collisions. We will present our results and discuss the implications of these measurements for observing p-wave pairing in quasi-1D. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J27.00005: The Bose-Glass Phase in Mean-Field Quasicrystalline Systems Dean Johnstone, Callum Duncan, Patrik Öhberg We study the ground state phases of the Bose-Hubbard model with disordered potentials for quasicrystalline systems, with a focus on the Bose-Glass phase. Generally speaking, disorder can lead to the formation of a Bose-Glass, which is characterised by the lack of global phase coherence across the lattice. Here, we look at two models; the interacting 2D Aubry-Andre model and disordered quasicrystalline vertex models. Unlike typical disorder in homogeneous, periodic systems, quasicrystalline models possess self-similarity. This leads to a fascinating interplay between correlated, quasiperiodic order and uncorrelated, random disorder. In this work, we use a mean-field percolation analysis of superfluid clusters to map out the critical points and phase regions of these disordered systems. When the long-range 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 long-range order present in the disorder term of the 2D Aubry-Andre model can result in some peculiarities to the physics of the Bose-Glass. 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 1/2-Laughlin 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 quasi-two-dimensional rotating trap, which will act as a bosonic analog of electrons in a magnetic field. For rotation frequencies close to the in-plane 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 one-dimensional 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 one-dimensional abelian anyons via bosons with an occupation-dependent hopping. Thereby, tunable two-particle 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 one-dimensional lattice anyons and its representation by one-dimensional bosons. The theory maintains the periodicity in the anyonic phase and includes current density as well as three-body 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 one-dimensional anyons in the continuum are experimentally accessible in purely bosonic systems. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Live |
J27.00008: Observation of a Smooth Polaron-Molecule 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 strongly-interacting with a Fermi sea is a long-standing challenge in many-body physics. For short-range interactions and zero temperature, most theories predict a first-order phase transition between a polaronic ground state and a molecular one. We study this question with an ultracold Fermi gas, utilizing a novel high-sensitivity 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 one-dimension Seth Grable, Noah Kamm, Harsh Mathur
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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 many-body T-matrix approximation. For a small spin-bias regime, the current in the vicinity of the superfluid transition temperature is strongly suppressed due to the formation of pseudogaps. For a large spin-bias 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 Live |
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 perturbatively-tractable limit of weak impurity-boson interactions many of its properties are known to depend only on the scattering length. Here we demonstrate that for strong (unitary) impurity-boson 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 impurity-boson potential via a single parameter. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J27.00012: Light-assisted 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 atom-Rydberg mixtures has led to the discovery of exotic bound long-range Rydberg molecules, with a ground state atom residing within the orbit of a Rydberg electron [2]. We now study the long-range interaction of Rydberg alkali-metal atoms with heteronuclear alkali-metal dimers in the regime of low molecular densities, such that the Rydberg-dimer interaction is dominated by van der Waals forces. We compute accurate C6 coefficients for a large set of atomic Rydberg states n2Lj interacting with ground state molecules [3]. For the (52S1/2)87Rb-KRb(J=0) collision pair, we predict large probabilities for forming long-range Rydberg-molecule bound states (trimers) with (n∼50)2D atomic Rydberg character, in a two-photon photoassociation scheme. We discuss the feasibility of detecting Rb-KRb trimers in currently available atom-molecule co-trapping experiments. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J27.00013: Quantum phases of Rydberg atoms in two-dimensional arrays Rhine Samajdar, Wen Wei Ho, Hannes Pichler, Mikhail Lukin, Subir Sachdev We describe the zero-temperature phases of two-dimensional arrays of neutral atoms, excited into Rydberg states and interacting via strong van der Waals interactions. Using the density-matrix 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 quantum-ordered phases stabilized by quantum fluctuations. These phases are surrounded by novel quantum phase transitions, which we analyze by finite-size scaling numerics and Landau theories. Our work highlights Rydberg quantum simulators in higher dimensions as promising platforms to realize exotic many-body 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/Su-Schrieffer-Heeger polarons in two dimensions Chao Zhang, Nikolai Prokof'ev, Boris Svistunov Previous studies find that when the electron-phonon coupling depends only on phonon momentum, the ground state properties feature a smooth crossover from weak to strong coupling. In the model with Peierls/Su-Schrieffer-Heeger (PSSH) coupling, when the interaction vertex depends also on the electron momentum, a competing-sectors transition between states with zero and nonzero momentum of the ground state has been found in one-dimension. 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 two-dimensional 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 System-Environment Coupling Wei Nie, Mauro Antezza, Yu-xi 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 environment-induced interaction. The strong system-environment coupling leads to a transition between the topological and nontopological phases. This phase transition not only presents an intrinsic relation between environment-induced 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 strong-coupling regime. |
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