Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session H05: Focus Session: Quantum Simulations in Low DimensionsFocus Live
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Sponsoring Units: DQI Chair: Ehsan Khatami, San Jose |
Wednesday, June 2, 2021 8:00AM - 8:30AM Live |
H05.00001: Interacting Fermions in Quasi-1D Invited Speaker: Ya-Ting Chang We explore the physics of interacting fermions in quasi-1D using $^6$Li confined to a 2D optical lattice. Motivated by recent theory, which suggests the usually severe three-body loss near a $p$-wave Feshbach resonance may be suppressed in 1D [1], we measured the three-body recombination rate of spin-polarized $^6$Li in quasi-1D [2]. We analyze the atom loss as a two-step cascade in which weakly bound dimers form prior to their loss arising from atom-dimer collisions to deeply bound diatomic molecules. We find a possible suppression in the rate of dimer relaxation with strong quasi-1D confinement, and for small field detuning from resonance. The implications for loss suppression due to the closed-channel character of this $p$-wave resonance remains to be fully understood. In addition, we study the effect of strong $s$-wave interactions on collective excitations in the Tomonaga-Luttinger liquid regime with a two-spin mixture of $^6$Li. We previously measured the dynamic structure factor for charge excitations using Bragg spectroscopy [3], while the spin excitations were inaccessible due to heating from spontaneous emission. We reduce the heating by using the narrow-linewidth 2S-3P transition (323 nm) and a two-spin mixture with large energy separation. We measure the spin and charge excitation spectrum, and thus realize the first direct measurement of spin-charge separation with tunable interactions. |
Wednesday, June 2, 2021 8:30AM - 9:00AM Live |
H05.00002: Realization of the Symmetry-Protected Haldane phase in Fermi-Hubbard Ladder Systems Invited Speaker: Pimonpan Sompet The concept of topology has strongly changed our understanding of quantum phases in many-body systems. The antiferromagnetic spin-1 Haldane chain has been used as the model for introducing these unexpected effects. The chain has symmetry-protected fourfold degenerate edge states with spin-1/2 localized at the two edges, while inside the chain, an excitation gap with a hidden long-range topological order prevails. Here, we introduce the experimental realization of the topological Haldane phase in Fermi-Hubbard ladders using ultracold-atom quantum simulators. This bases on the AKLT model in which a spin-1 particle is built-up out of two spin-1/2 particles. From the results, we directly observe both edge and bulk characteristics by harvesting our unique detection scheme with full spin and density resolution that allows us to construct string order parameters. By reducing the Hubbard interaction strength of the system far from the Heisenberg regime, we observe the robustness of the phase against the density fluctuations. |
Wednesday, June 2, 2021 9:00AM - 9:12AM Live |
H05.00003: Confinement and Mott transitions of dynamical charges in 1D lattice gauge theories Matjaz Kebric, Luca Barbiero, Christian Reinmoser, Ulrich J Schollwoeck, Fabian Grusdt Lattice gauge theories (LGTs) have become a valuable tool to study strongly correlated condensed matter systems. This becomes in particular interesting when gauge degrees of freedom are coupled to matter since they allow us to study the complex problem of confinement. However, when the lattice is doped and matter becomes dynamical the clear notion of confinement becomes complicated. Here we study a one-dimensional (1D) Z2 LGT model where the gauge fields are coupled to dynamical charges with confining Z2 electric field and repulsive nearest-neighbour interactions. We map our model to a local string-length Hamiltonian where we link the confinement in the Z2 LGT model to a broken translational symmetry in the string-length basis. In addition we study the Mott transition of the charges at a specific filling of n=2/3. We find that the metallic phase of the confined Luttinger liquid is characterized by a hidden off-diagonal quasi-long-range order. Furthermore we map the 1D Z2 LGT model to a t-Jz model which can be implemented in cold atom experiments by using the Rydberg dressing schemes; thus, we propose a way to directly test our theoretical predictions. |
Wednesday, June 2, 2021 9:12AM - 9:24AM Live |
H05.00004: Simulating the Haldane model with ultracold atoms: different perspectives & unexpected results Michele Modugno The Haldane model is a paradigmatic two-dimensional tight-binding model describing a topological insulator, characterized by the breaking of the time-reversal symmetry due the presence of a microscopic magnetic field with vanishing flux across the unit cell. Recently, its phase diagram has been experimentally realized by means of ultracold atoms in a shaken optical lattice [Jotzu et al., Nature 515, 237 (2014)]. In its original formulation the Haldane model was constructed by using the so-called Peierls substitution (PS), a widely employed approach that consists in adding a phase factor proportional to the line integral of the vector gauge field to the ‘bare’ tunneling coefficients. However, the conditions of applicability of the PS are explicitly violated in the Haldane model, as in many other cases considered in the literature, that I will review in this talk from an historical perspective. Despite the failure of the PS, we have shown that the general structure of the Haldane Hamiltonian is protected by the symmetries of the system and that the values of the tunneling coefficients can be obtained from simple closed expressions in terms of gauge invariant, measurable properties of the spectrum. Indeed, they match with great accuracy the ab-initio values obtained by means of the maximally localized Wannier functions. We have also investigated the correspondence between the tight-binding Floquet Hamiltonian of a periodically modulated honeycomb lattice and the original Haldane model. Remarkably, though the two systems share the same topological phase diagram, the corresponding Hamiltonians are not equivalent, the one of the shaken lattice presenting a much richer structure. |
Wednesday, June 2, 2021 9:24AM - 9:36AM Live |
H05.00005: Benchmarking an approximation hypothesis for localized 1D Fermi-Hubbard systems on a cold-atom quantum simulator Bharath Hebbe Madhusudhana, Sebastian Scherg, Thomas Kohlert, Immanuel F Bloch, Monika Aidelsburger Quantum simulators have made significant progress towards simulating quantum many-body systems, which are intractable to current numerical and theoretical methods. However, state-of-the art quantum simulators are noisy and limited in the variability of the initial state of the dynamics and the observables that can be measured. Despite these limitations, here we show that such a quantum simulator can be used practically to in-effect solve for the dynamics of a many-body system. Any computation of the dynamics of quantum many-body systems is met with challenges arising from the exponentially growing dimension of the Hilbert space. A natural countermeasure is to relax the tolerance and seek approximate solutions. A key feature of approximate methods is the error estimate, which allows us to determine when it is reliable. However, not every approximation ansatz has a well established error estimate. We show that a neutral atom quantum simulator can be used to benchmark such theories, in the absence of an error estimate. We consider a localized 1D Fermi-Hubbard system where and develop an efficient approximate theory. Our approximate theory does not have an error estimate and therefore, we use a quantum simulator to benchmark its performance in terms of accuracy of its outcome. Finally, we identify the nature of the many-body dynamics for which our approximate theory breaks down. This represents an opportune regime for the deployment of quantum simulators in the future. |
Wednesday, June 2, 2021 9:36AM - 9:48AM Live |
H05.00006: Prediction of Toric Code Topological Order from Rydberg Blockade Ruben Verresen, Mikhail Lukin, Ashvin Vishwanath The physical realization of Z2 topological order as encountered in the paradigmatic toric code has proven to be an elusive goal. In this talk, I will show that this phase of matter can be created in a two-dimensional array of strongly interacting Rydberg atoms on a ruby lattice. A Rydberg "PXP" blockade model effectively realizes a monomer-dimer model on the kagome lattice with a single-site kinetic term, for which we observe a Z2 spin liquid using the numerical density matrix renormalization group method. This phase is shown to persist upon including realistic, algebraically-decaying van der Waals interactions. Moreover, one can directly access the topological loop operators of this model, which can be measured experimentally using a dynamic protocol, providing a smoking gun experimental signature of the topological phase. The trapping of an emergent anyon and the realization of different topological boundary conditions show that this set-up could be used for exploring fault-tolerant quantum memories. |
Wednesday, June 2, 2021 9:48AM - 10:00AM On Demand |
H05.00007: Observing the effect of dimensionality on the stability of strongly interacting fermionic superfluids Lennart Sobirey, Hauke Biss, Niclas Luick, Markus Bohlen, Henning Moritz, Thomas Lompe We use ultracold Fermi gases as a model system to directly probe the influence of dimensionality on the stability of fermionic superfluids. Using momentum-resolved Bragg spectroscopy, we measure the superfluid gap of of two- and three-dimensional homogeneous Fermi gases over a wide range of interaction strengths. We find that the superfluid gap follows a universal function of the chemical potential, irrespective of the dimensionality. Comparing our results with other fermionic superfluids suggests that strong correlations and short coherence lengths are more important for the stability of fermionic superfluids than the dimensionality of the system. |
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