Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 67, Number 7
Monday–Friday, May 30–June 3 2022; Orlando, Florida
Session X04: Topology in Cold GasesRecordings Available

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Chair: Lindsay LeBlanc, UAlberta Room: Salon 3/4 
Friday, June 3, 2022 8:00AM  8:12AM 
X04.00001: Experimental realization of a fermionic spinmomentum lattice Julio T Barreiro, Paul Lauria, Nigel R Cooper, WeiTing Kuo We experimentally realize a spinmomentum lattice with a homogeneously trapped Fermi gas. The lattice is created via cyclically rotated atomlaser couplings between three bare atomic spin states, and are such that they form a triangular lattice in a synthetic spinmomentum space. We demonstrate the lattice and explore its dynamics with spin and momentumresolved absorption imaging. This platform will provide new opportunities for synthetic spin systems and the engineering of topological bands. In particular, the use of three spin states in two spatial dimensions would allow the simulation of synthetic magnetic fields of high spatial uniformity, which would lead to ultranarrow Chern bands that support robust fractional quantum Hall states. 
Friday, June 3, 2022 8:12AM  8:24AM 
X04.00002: Topological pumping in the strongly correlated regime AnneSophie Walter, Zijie Zhu, Joaquin Minguzzi, Marius Gächter, Kilian Sandholzer, Stephan Roschinski, Konrad G Viebahn, Tilman Esslinger A topological pump can be regarded as the onedimensional counterpart to the quantum Hall effect, in which time plays the role of a second dimension. Quantisation of charge transport is achieved by slowly encircling a topological transition point in Hamiltonian parameter space. Previously, topological pumps have been realised with noninteracting and meanfield states in synthetic quantum systems, such as ultracold atoms and photonics. However, the fate of quantised pumping in the strongly correlated regime has remained out of reach to date. Here, we present recent experimental progress towards investigating the effects of Hubbard interactions on topological charge transport of ultracold fermions. Our measurements suggest significant deviations from the quantised value for attractive and repulsive interactions. We compare our results to recent theoretical studies that predict a breakdown of pumping in the Mott regime. 
Friday, June 3, 2022 8:24AM  8:36AM 
X04.00003: Quantized transport of solitons in nonlinear Thouless pumps: From Wannier drags to ultracold topological mixtures Nader Mostaan, Fabian Grusdt, Nathan Goldman Recent progress in synthetic lattice systems has opened the door to novel explorations of topological matter. In particular, photonic devices and ultracold matter waves offer the unique possibility of studying the rich interplay between topological band structures and tunable nonlinearities. In this emerging field of nonlinear topological physics, a recent experiment revealed the quantized motion of localized nonlinear excitations (solitons) upon driving a Thouless pump sequence; the reported observations suggest that the quantized displacement of solitons is dictated by the Chern number of the band from which they emanate. In this work, we elucidate the origin of this intriguing nonlinear topological effect, by showing that the motion of solitons is established by the quantized displacement of Wannier functions. Our general theoretical approach, which fully clarifies the central role of the Chern number in solitonic pumps, provides a rigorous framework for describing the topological transport of nonlinear excitations in a broad class of physical systems. Exploiting this interdisciplinarity, we introduce an interactioninduced topological pump for ultracold atomic mixtures, where solitons of impurity atoms experience a quantized drift resulting from genuine interaction processes with their environment. 
Friday, June 3, 2022 8:36AM  8:48AM 
X04.00004: Wavepacket dynamics in topological Floquet bands Alexander C Hesse, Christoph Braun, Raphaël SaintJalm, Immanuel Bloch, Monika Aidelsburger Floquet engineering, i.e., the periodic modulation of a system’s parameters, has proven as a powerful tool for the realization of quantum systems with exotic properties, which are otherwise not accessible in static realizations. We have engineered such systems on our experimental platform, which consists of bosonic atoms in a periodically driven optical honeycomb lattice. Depending on the driving parameters several topological phases can be realized, including genuine outofequilibrium topological phases without any static analogue [1]. 
Friday, June 3, 2022 8:48AM  9:00AM 
X04.00005: Realization of a nonHermitian optical Raman lattice for ultracold fermions Entong ZHAO, Chengdong HE, Zejian Ren, Ka Kwan Pak, Yujun Liu, GyuBoong Jo The recent advances in nonHermitian physics open new possibilities for exploring unprecedented quantum states in an open atomic system. In our previous study[1], we have realized nonHermitian spinorbit coupled bands for ultracold fermions in bulk, and demonstrated the topological nature of nonHermitian energy band near the band closing point when the ParityTime symmetry breaking transition occurs. In this talk, we report our progress on the experimental development of the nonHermitian optical Raman lattice, which generalizes nonHermitian spinorbit coupling into the lattice system. Focusing on the time evolution of spin texture in Bloch bands, we explore the distinct features induced by a highly controllable spindependent dissipation and spinorbit coupling. It is expected that this nonHermitian platform would allow us to further expand the possibilities of studying the nonHermitian topological phases in lattices. 
Friday, June 3, 2022 9:00AM  9:12AM 
X04.00006: Twodimensional momentum state lattices Shraddha Agrawal Cold atoms offer a clean, precise, and highly controllable platform for quantum simulation. The technique of momentum state lattices (MSLs) in one dimension allows the spectroscopic engineering of synthetic lattices with single site precision, offering independent control over all tunneling terms and site energies. In this talk, I present the extension of 1D MSLs to engineer 2D synthetic lattices of laser coupled atomic states. The platform of 2D MSLs offer the potential to explore topological, disordered, and kinetically frustrated lattice models in two dimensions. Due to our experimental switch from Rb87 to K39, our system offers tunable interactions via magnetic Feshbach resonance. The ability to augment the aforementioned twodimensional models with tunable interactions promises an exploration of a broad range of nonlinear lattice phenomena. 
Friday, June 3, 2022 9:12AM  9:24AM 
X04.00007: Interaction induced topology in a BoseHubbard chain under nonHermitian Drive William N Faugno, Tomoki Ozawa Exotic topological phases with no analogue in traditional static Hermitian systems have been observed in Floquet and nonHermitian systems. We propose a model that combines nonHermiticity and Floquet engineering to realize topological energy spectrum in a 1D bosonic system. Our Hamiltonian is a 1D Bose gas with an asymmetric density dependent nonHermitian gauge field. The single particle spectrum is topologically trivial while the spectrum with multiple particles has a nontrivial winding number, suggesting the topology arises from interactions. We calculate a nontrivial winding number of 2 under periodic boundary conditions if there are two particles in the system. Equivalently, we observe a skin effect in the open boundary geometry, only if there are multiple particles in the system. We further find that the spectrum can be separated into two sectors: one where the particles cluster and one where the particles avoid each other. We derive an effective theory that accurately describes the properties of the clustering sector as a nonHermitian SSH model. Finally, we propose that our model can be realized in bosons trapped in optical lattices or in coupled optical waveguide arrays. 
Friday, June 3, 2022 9:24AM  9:36AM 
X04.00008: Topological charge pumping in a Fermi gas with Hubbard interactions Eric Bertok, Jan Albrecht, Fabian HeidrichMeisner, Armando Aligia We consider charge pumping in onedimensional interacting systems of spinful fermions, where each species is described by a (possibly shifted) RiceMele model.The ionic Hubbard model [13] is visited twice during a pump cycle. It hosts three phases: The MottInsulating (MI) phase is separated from the bandinsulating (BI) phase via a spontaneously dimerized (SDI) phase. A dimerized hopping connects the BI and MI phases without closing the charge gap. We show via the manybody polarization and timedependent calculations of the integrated current that a closed loop around one charge critical point of the ionic Hubbard model leads to the pumping of a single unit of charge per pump cycle in the adiabatic limit, as opposed to two charges for a usual RiceMele pump. Pumping through the SDI phase does not change the quantization of pumped charge, contrary to what was recently reported in [4]. 
Friday, June 3, 2022 9:36AM  9:48AM 
X04.00009: NonAbelian Euler topology in ultracold atoms RobertJan Slager, Adrien Bouhon, Nur Unal Topological insulators (TIs) are gapped quantum phases that have a topological nature by virtue of protecting symmetries. Following time reversal symmetry (TRS) protected TIs, past years have seen remarkable progress in characterizing topological materials taking into account crystal symmetries. These pursuits also revealed fragile invariants that can be trivialized by gap closings with trivial bands, rather than involving those having opposite topological charge. An archetypal novel invariant emerging from such studies, which goes beyond symmetry eigenvalue indicated phases and relates to refined partitioning schemes is Euler class. It acts as the fragile crystallineprotected analogue of Chern number in systems having C_{2}T [product of twofold rotations and TRS] or PT [product of parity P and TRS] symmetry. Moreover, band nodes in Euler class models have charges that have nonAbelian braiding properties, enabling the study of nonAbelian physics essentially in a single particle setting and making their experimental realization highly desirable. On another front, ultracold atomic gases have proven versatile platforms for exploring topological phenomena with particular advances in periodic driving and artificial gauge fields, calling for expansion of these notions to out of equilibrium and bringing new classification schemes. In light of recent experiments calibrated to explore Euler topology, we here investigate the dynamics of Euler class in optical lattices. We study nonAbelian Euler properties in different outofequilibrium settings and identify unique observable signatures. 
Friday, June 3, 2022 9:48AM  10:00AM 
X04.00010: NonHermitian ManyBody Localization of Coupled HatanoNelson Chains Kuldeep Suthar, YiCheng Wang, YiPing Huang, JhihShih You, HsiangHua Jen The physics of nonHermitian systems has attracted significant interests in recent years. The phenomena of nonHermiticity originate from an exchange of energy or particles with environment and leads to several rich properties such as paritytime symmetry breaking, exceptional points unique to nonHermitian topology etc. Recently, it has been shown that a nonHermitian system with random disorder or quasiperiodic potential possessing timereversal symmetry exhibit complexreal transition. In this work, we explore the eigenspectrum and localization properties of the interacting coupled HatanoNelson chains in the presence of random disorder potential. In contrast to the previous studies of the spinless fermionic system, the twochain system shows a complexreal transition which does not coincide to the localization transition. Moreover, the critical coupling strength of the transition decreases as the ratio of respective nonreciprocal hoppings varied. We further investigate the spectral statistics and dynamical properties of the system. Our study opens up a direction towards an exploration of the critical effects of disordered nonHermitian manybody systems in coldatom experiments. 
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