Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session PP07: V: Ultracold Atomic Gases |
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Sponsoring Units: DAMOP Chair: Ivor Kresic, Technical University of Vienna Room: Virtual Room 7 |
Tuesday, March 21, 2023 9:00AM - 9:12AM |
PP07.00001: Engineering a Quantized Integer Hall Response in Non-Interacting Bosonic Hamiltonians Joshuah T Heath, Vincent P Flynn, Andrew Cupo, Emilio Cobanera, James D Whitfield, Lorenza Viola The TKNN formulation of the integer quantum Hall effect states that the transverse conductivity of a two-dimensional electron system subjected to low temperatures and an external magnetic field is directly related to the Chern number characterizing the non-trivial topology of the underlying electronic band structure. We revisit the original TKNN argument for non-interacting (quadratic) bosonic Hamiltonians by relaxing the requirement that they be thermodynamically stable, while maintaining dynamical stability, and provide a protocol for engineering quantized transverse response in topologically non-trivial regimes. This is done by generalizing the Smrcka-Streda formulation of the Hall conductivity for non-interacting many-boson systems, wherein a non-thermal distribution yielding quantized transverse response of the Hamiltonian density is identified. We then explore the possibility of quantized response with this non-thermal distribution via numerical simulations of the anomalous quantum Hall effect in number non-conserving bosonic models on the honeycomb and kagome lattices. Our work provides a possible recipe for the experimental detection of topologically non-trivial phases of bosons in two-dimensional synthetic photonic materials. |
Tuesday, March 21, 2023 9:12AM - 9:24AM |
PP07.00002: Measuring the Chern number with weakly interacting spin-orbit-coupled Bose gases in optical lattices Saubhik Sarkar, Taylor Cey, Abhijeet Alase, David L Feder The quantification of topological invariants for tight-binding Hamiltonians with certain crystalline point group symmetries is well-studied, and in particular, the Chern number has been shown to be expressible in terms of the eigenvalues of the symmetry operator at the high-symmetry points of the Brillouin zone. In recent years, it has become possible to utilize this relation in cold atom experiments to measure the Chern number by loading spinor BECs with spin-orbit coupling onto 2D optical lattices. Spin polarization measurements are used to quantify the topological invariant, although so far it has been limited to Chern number 1. A recent experimental proposal based on Chern insulators with additional spin-space symmetries has paved the way for extracting higher Chern number with better resolution by performing polarization measurements only at those high-symmetry points for an ideal BEC. In this work, we go beyond the assumption that the BEC is non-interacting and study the effects of interactions that are weak enough not to destroy the condensation but can still be comparable or even stronger than the band gaps of the spin-orbit coupling Hamiltonian. Our framework is based on a mean-field treatment including fluctuations. Aside from quantifying the deviations in Chern number measurements from the non-interacting limit, we are able to investigate other interesting effects arising from the competition between the interactions, spin-orbit coupling, and the optical lattice potential under realistic experimental conditions. |
Tuesday, March 21, 2023 9:24AM - 9:36AM |
PP07.00003: Quantum motional state Dicke squeezing by cavity self-organization of ultracold atoms Ivor Kresic We study the transverse optomechanical self-organization of an ultracold bosonic gas in a ring cavity driven by an external laser. By modeling the light-matter interaction with a many-body Hamiltonian, we demonstrate the spontaneous generation of Dicke squeezing and many-particle entanglement of atomic motional states, occurring due to self-organization of photons and atoms in the stripe phase. Once generated, these squeezed states are maintained after a sudden switch-off of the laser pump in a dissipative cavity. Our results highlight the potential of using self-organization of atomic motion as a tool for emerging quantum technologies. |
Tuesday, March 21, 2023 9:36AM - 9:48AM |
PP07.00004: The Unitary Fermi Gas at Large-N and Low Rank Gregory Bentsen, Brian Swingle We study the BCS-BEC crossover in the attractive Fermi gas using large-N techniques. Whereas the BCS and BEC limits are both well described by weakly-interacting theories, the scattering length diverges at the crossover, yielding a strongly-interacting Fermi gas. To access the physics in this strongly-interacting regime, we introduce a disordered model of N fermions coupled via M bosons, where both M,N are taken to be large. In this large-N limit we compute the electron Green's function, transition temperature, gap, and Bertsch parameter by numerically solving the system's Schwinger-Dyson equations. Further, we use the ratio gamma = M/N of bosons to fermions, also called the `rank' of the model, as a perturbative parameter to analytically study the unitary point. We compare our results to direct experimental measurements and previous mean-field studies. |
Tuesday, March 21, 2023 9:48AM - 10:00AM |
PP07.00005: Understanding the interplay of particle conservation and long-range coherence Emanuele G Dalla Torre, Matthew Reagor Lasers and Bose-Einstein condensates (BECs) exhibit macroscopic quantum coherence in seemingly unrelated ways. Lasers possess a well-defined global phase and are characterized by large fluctuations in the number of photons. In BECs of atoms, instead, the number of particles is conserved and the global phase is undefined. Here, we use gate-based quantum circuits to create a unified framework that connects lasers and BEC states. Our approach relies on a scalable circuit that measures the total number of particles without destroying long-range coherence. We introduce two complementary probes of global and relative phase coherence, and study how they are affected by measurements of the particle number. We find that particle conservation {it enhances} long-range phase coherence, highlighting a mechanism used by superfluids and superconductors to gain phase stiffness. |
Tuesday, March 21, 2023 10:00AM - 10:12AM |
PP07.00006: Anomalous multicritical phenomena and frustration induced by synthetic magnetic fields Jinchen Zhao, Myung-Joong Hwang We study the anomalous multicriticality and superradiant phase transition (SPT) of a one-dimensional Dicke lattice under broken time-reversal symmetry induced by synthetic magnetic fields [1]. We find that the universality class of SPT depends on the total magnetic flux, which divides the phase diagram into a standard SPT characterized by mean-field exponents and an anomalous SPT where non-mean-field exponents appear on both sides of the transition. In addition, correlations and fluctuations are bounded in the anomalous normal phase while divergent in the anomalous superradiant phase, leading to discontinuity despite it being a second-order phase transition. We attribute this non-mean-field behavior in the anomalous normal phase to the asymmetric dispersion relation due to time-reversal symmetry breaking. In the broken symmetry phase, we show that the complex nearest-neighbor hopping energy leads to long-range interactions in the mean-field, the competition of which induces varying degrees of frustration [2] in order parameters analogously to the J1-J2 Ising model. Finally, we find the resulting multicritical points can have two distinct critical exponents on both sides of the critical point. Our work demonstrates the interplay between broken time-reversal symmetry and frustration in bosonic lattice systems can lead to anomalous critical phenomena that cannot be found in fermionic or time-reversal symmetric quantum optical systems. |
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