Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 68, Number 7
Monday–Friday, June 5–9, 2023; Spokane, Washington
Session H08: Quantum Phases in Optical Lattices II |
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Chair: Joseph Thywissen, University of Toronto Room: 206 C |
Wednesday, June 7, 2023 8:00AM - 8:12AM |
H08.00001: Quantum gas microscopy of a geometrically frustrated Hubbard system Liyu Liu, Jirayu Mongkolkiattichai, Davis A Garwood, Jin Yang, Peter Schauss Frustrated quantum systems host exotic phases such as spin liquids, while their extensive ground state degeneracy poses a significant challenge to condensed matter theory. Here we present our recent work on quantum simulation of electronic systems using ultracold atoms arranged in a geometrically frustrated lattice. A triangle is the paradigm example for geometric frustration. In a triangular lattice, the degree of frustration is tunable via interactions. In the Heisenberg limit, 120 degree spiral order is expected in contrast to the staggered ordered in the square lattice. In this talk, we present a Mott insulator of lithium-6 on a symmetric triangular lattice with a lattice spacing of 1003 nm. The atoms in the triangular lattice are imaged in-situ with an imaging fidelity of 98% [1]. We calibrated tunneling and interaction by lattice modulation spectroscopy. The temperature of our atoms is below one-fifth of the Fermi temperature before loading to the lattice. We used a spin removal technique [2] to resolve either spin up or down to detect spin-spin correlations. We measured the nearest neighbor spin-spin correlations versus different interactions and compare the results to a numerical linked cluster expansion calculation as well as Quantum Monte Carlo simulations [3]. Currently, we are planning to implement spin-resolved imaging via Stern-Gerlach splitting to reach full density resolution [4] and explore a bound state in a strongly repulsive interacting system [5]. |
Wednesday, June 7, 2023 8:12AM - 8:24AM |
H08.00002: Non-local pairing and charge density wave in the attractive Fermi-Hubbard model Botond Oreg, Thomas R Hartke, Carter Turnbaugh, Ningyuan Jia, Martin W Zwierlein The 2D Fermi-Hubbard model with attractive interactions is predicted to exhibit exotic phases such as a pseudogap regime or charge density wave ordering. We explored the crossover from tightly bound to delocalized pairs, harnessing the capabilities of our quantum gas microscope, extracting the full spin and charge information with single atom resolution during each experimental run. Complete fermion pairing is observed above a critical interaction strength by vanishing total spin fluctuations, and the delocalization of the pairs can be revealed from the finite on-site spin fluctuations. In the strongly correlated regime, the size of the fermion pairs approaches the interatomic spacing, which drives the system into a charge density wave (CDW), a many-body ordered state. With the ability to address the spin and charge simultaneously, we are also able to probe the polaronic nature of a single spin moving across a background CDW. These advances pave the way to investigate the numerically intractable spin and charge doped regime of the Fermi-Hubbard model and to in-situ observe a fermionic superfluid in a lattice. |
Wednesday, June 7, 2023 8:24AM - 8:36AM |
H08.00003: Emergent Bose-Fermi mixture from a spin-imbalanced Hubbard gas Ningyuan Jia, Thomas R Hartke, Botond Oreg, Carter Turnbaugh, Martin W Zwierlein The attractive Fermi-Hubbard model with spin and charge doping is predicted to host a variety of exotic phases, such as FFLO pairing and d-wave antiferromagnetism. In this work, by employing a quantum gas microscope, the microscopic behavior of fermion pairs at finite magnetization is explored at various densities and magnetizations. We first demonstrate the robustness of fermion pairing against spin-imbalance by observing the strongly suppressed spin fluctuations. By measuring the excess density around minority atoms, we are able to observe a crossover from on-site doublons to extended pairing with decreasing interaction strength. With higher magnetization, the Pauli hole is observed between excess spins via singlon-singlon correlations, indicating the emergence of a degenerate Fermi surface. We further reveal the repulsive nature between the bosonic pairs and excess fermions by measuring their density correlation, confirming that the system can be effectively described as a hard-core Bose-Fermi mixture. Finally, by using local correlations, we are able to characterize the spin-imbalanced Fermi-Hubbard gas via different categories at various densities and magnetizations, based on the presence or absence of many-body ordering and Pauli repulsion. |
Wednesday, June 7, 2023 8:36AM - 8:48AM |
H08.00004: Structural complexity of Fermi Hubbard model snapshots in two dimensions Eduardo Ibarra Garcia Padilla, Richard T Scalettar, Ehsan Khatami In recent years, the measure of structural complexity has emerged as a useful technique to detect the location of phase transitions. This concept relies on a series of coarse-graining steps performed on concatenated samples, which at the end of the procedure produces a single number. By detecting sharp changes in the structural complexity as a tuning parameter changes one is able to deduce the location of the transitions. This approach lends itself well to the study of experimental snapshots obtained with quantum gas microscopy, which correspond to projective measurements of local densities. In this work we study the evolution of the structural complexity in snapshots of the two-dimensional Fermi Hubbard model across different filling fractions and temperatures spanning the antiferromagnetic regime and the strange metallic regions. |
Wednesday, June 7, 2023 8:48AM - 9:00AM |
H08.00005: Doping a frustrated Fermi-Hubbard magnet Lev H Kendrick, Muqing Xu, Anant Kale, Youqi Gang, Geoffrey Ji, Richard T Scalettar, Martin Lebrat, Markus Greiner The Fermi-Hubbard model on the anisotropic triangular lattice is a fundamental setting for studying the effects of geometric frustration on strongly correlated fermions, which is believed to generate intriguing magnetic phases such as quantum spin liquids. The model’s phase diagram, however, remains debated even at half-filling, and is still more unclear in the presence of doping. Here we use a quantum gas microscope to probe the local spin order of the anisotropic triangular Fermi-Hubbard model as a function of anisotropy and doping. In Mott insulating samples, we observe how frustration weakens magnetic correlations and drives a transition from a collinear Néel antiferromagnet to a short-range 120· spiral phase. Upon doping, magnetic correlations show a pronounced particle-hole asymmetry and suggest a transition to ferromagnetism at heavy particle doping. This work opens the door for future studies of possible chiral or superconducting phases in triangular lattices, and paves the way towards realizing non-bipartite square lattice Hubbard models that may be crucial in modeling the superconducting cuprates. |
Wednesday, June 7, 2023 9:00AM - 9:12AM |
H08.00006: Transport in the 2D Fermi-Hubbard model: Lessons from weak coupling Thomas G Kiely, Erich J Mueller Recent cold atom experiments have observed bad and strange metal behaviors in strongly-interacting Fermi-Hubbard systems. Motivated by these results, we calculate the thermoelectric transport properties of a 2D Fermi-Hubbard system in the weak coupling limit using quantum kinetic theory. We find that many features attributed to strong correlations are also found at weak coupling. In particular, for temperatures T>t the electrical resistivity is nearly linear in temperature despite the fact that the quasiparticle scattering rate is non-linear and changes by nearly an order of magnitude. We argue that this asymptotic behavior is a general feature of systems with a finite spectral width, which implies that there is no MIR bound on the resistivity in single-band models. Due to nesting, the T-linear resistivity persists down to T=0 at half filling. Our work sheds light on the transport regimes accessible in ultracold atom experiments, which can differ substantially from those in condensed matter systems. Disentangling these band-structure effects from the physics of strong correlations is a major challenge for future experiments. |
Wednesday, June 7, 2023 9:12AM - 9:24AM |
H08.00007: Spin dynamics dominated by resonant tunneling into molecular states Yoo Kyung Lee, Hanzhen Lin, Wolfgang Ketterle Optical lattices and Feshbach resonances are two of the most ubiquitously-used tools in atomic physics, allowing for the precise control, discrete confinement, and broad tunability of interacting atomic systems. Using a quantum simulator of lithium-7 atoms in an optical lattice, we investigate Heisenberg spin dynamics near a Feshbach resonance. We find novel resonance features in spin-spin interactions that can only be explained by lattice-induced resonances, which have never been observed before. We use these resonances to adiabatically convert atoms into molecules in excited bands. Further, we also report the first experimental evidence for off-site contact interactions in an optical lattice. Lattice-induced resonances should be of general importance for studying strongly-interacting quantum many-body systems in optical lattices. |
Wednesday, June 7, 2023 9:24AM - 9:36AM |
H08.00008: Error correction assisted determination of the non-local membrane order parameter Junhyeok Hur, Wonjun Lee, Kiryang Kwon, Gil Young Cho, Jae-yoon Choi Non-local order parameters are expected to distinguish exotic phases of the quantum system. The membrane order parameter, which can determine the phases of the Bose-Hubbard model in two dimensions, is an example of such non-local order parameter. However, the membrane order parameter in the optical lattice system is difficult to measure because of the parity projected measurement and incoherent holes. In this presentation, we will introduce the method to detour the errors from the incoherent holes by introducing the error correction scheme. This error correction method is applied to analyze the superfluid to Mott Insulator system in an optical lattice. We prepared 1200 atoms in the optical lattice and took snapshots of the atoms with different values of J/U with quantum gas microscope imaging. Our system has incoherent holes with probability p = 0.02 from the thermal fluctuation and the losses during the imaging process [1]. Using the error correction assisted membrane order parameter, we could identify the phase boundary between the superfluid and Mott Insulator phases. Furthermore, the scaling depending on the system size consists of the theoretically expected result. Our error correction scheme can be generalized to any system where errors from incoherent sources are unavoidable. |
Wednesday, June 7, 2023 9:36AM - 9:48AM |
H08.00009: Ferromagnetism in doped Hubbard models in optical lattices Rhine Samajdar, R. N Bhatt The search for ferromagnetism in the Hubbard model has been a problem of outstanding interest since Nagaoka’s original proposal in 1966. Recent advances in quantum simulation have today enabled the study of tunable doped Hubbard models in ultracold atomic systems. Here, we study a variant of such a model wherein any second electron on a single lattice site is weakly bound compared to the first1. Employing large-scale density-matrix renormalization group and exact diagonalization calculations in both one and two spatial dimensions, we establish the existence of high-spin ground states on the nanoscale, study their subtle interplay with lattice geometries, and investigate the competition between ferromagnetic and stripe orders. We also discuss the experimental realization of this system in current-generation optical lattice platforms via the careful use of Feshbach resonances. |
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