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 C27: Topological States in AMO Systems IFocus Live
|
Hide Abstracts |
Sponsoring Units: DAMOP DCMP Chair: Sumanta Tewari, Clemson University |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C27.00001: Hall drift of fractional Chern insulators in few-boson systems Cécile Repellin, Julian Leonard, Nathan Goldman Realizing strongly-correlated topological phases of ultracold gases is a central goal for ongoing experiments. And while fractional quantum Hall states could soon be implemented in small atomic ensembles, detecting their signatures in few-particle settings remains a fundamental challenge. In this work, we numerically analyze the center-of-mass Hall drift of a small ensemble of hardcore bosons, initially prepared in the ground state of the Harper-Hofstadter-Hubbard model. By extracting the Hall conductivity in a wide range of the magnetic flux, we identify an emergent Hall plateau compatible with a fractional Chern insulator state: the width of the plateau agrees with the spectral and topological properties of the prepared ground state, while the Hall conductivity approaches a fractional value determined by the many-body Chern number. A comparison with a direct application of Streda’s formula is also discussed. Our calculations suggest that fractional Chern insulators can be detected in cold-atom experiments, using available detection methods. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C27.00002: Bosonic Pfaffian State in the Hofstadter-Bose-Hubbard Model Felix Palm, Maximilian Buser, Julian Leonard, Monika Aidelsburger, Ulrich Joseph Schollwoeck, Fabian Grusdt Topological states of matter, such as fractional quantum Hall states, are an active field of research due to their exotic excitations. In particular, ultracold atoms in optical lattices provide a highly controllable and adaptable platform to study such new types of quantum matter. However, the effect of a coarse lattice on the topological states often remains poorly understood. Here we use the density-matrix renormalization-group (DMRG) method to study the Hofstadter-Bose-Hubbard model at filling factor ν = 1 and find strong indications that at α = 1/6 magnetic flux quanta per plaquette the ground state is a lattice analog of the continuum Pfaffian. We study the on-site correlations of the ground state, which indicate its paired nature at ν = 1, and find an incompressible state characterized by a charge gap in the bulk. We argue that the emergence of a charge density wave on thin cylinders and the behavior of the two- and three-particle correlation functions at short distances provide evidence for the state being closely related to the continuum Pfaffian. The signatures discussed here are accessible in cold atom experiments and the Pfaffian-like state seems readily realizable in few-body systems using adiabatic preparation schemes. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C27.00003: Synthetic Dimensions with Rydberg Atoms Sohail Dasgupta, Soumya K Kanungo, F Barry Dunning, Thomas Charles Killian, Kaden Hazzard Recent experiments in our collaboration have created synthetic dimensions using Rydberg levels of ultracold 84Sr atoms as synthetic lattice sites and microwaves as synthetic tunnelings between the sites. These synthetic dimensions have fully controllable tunnelings and on-site potentials, allowing experiments to study topological band structures and novel many-body physics. To achieve these goals, it is crucial to understand the system beyond an idealized picture, including effects such as unwanted off-resonant levels, terms beyond the rotating-wave-approximation, and decoherence. We theoretically evaluate these and show that they do not present fundamental obstacles to realizing large synthetic dimensions. We will discuss comparisons with ongoing experiments, which have observed topological edge states in the Su-Schrieffer-Heeger (SSH) model consisting of alternating weak and strong tunnelings in 4- and 6-site synthetic dimension systems consisting of pairs of 3S1,m=0 and 3P0 levels with principal quantum numbers n=57-59. Interestingly, we find that the decoherence in the synthetic dimension differs qualitatively from typical real space decoherence, which may lead to new phenomena. This establishes the framework in which to study interacting topological models. |
Monday, March 15, 2021 3:36PM - 3:48PM Not Participating |
C27.00004: Building quantum dots and Laughlin puddles from optical photons Nathan Schine Building a synthetic material out of light requires control of three basic ingredients: photon dispersion, interactions, and the population within the (many-)photon state space. Confining optical photons in an optical cavity allows tailoring the single particle Hamiltonian. A single mode cavity provides a zero-dimensional quantum dot, while degenerate multimode cavities give rise to one- or two-dimensional harmonic confinement and even an effective magnetic field. Hybridizing cavity photons with Rydberg excitations of a cold atomic gas turns non-interacting photons into strongly-interacting cavity Rydberg polaritons, quasiparticles which inherit their motional dynamics from their photonic component and gain strong interactions from their Rydberg component. In a quantum dot we observe these interactions giving rise to strong anti-bunching of photons travelling through the system. When we grant polaritons access to a degenerate Landau level of cavity states, they collide and reorder into topologically nontrivial material states. Ongoing work to engineer dissipation in this system to autonomously cool into a topologically ordered ground state will permit the preparation of large topological materials and the direct manipulation of anyonic excitations. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C27.00005: Determination of Chern Number by Measurement of Spin Polarization of Spin-Orbit Coupled Ultracold Atoms in Optical Lattices Abhijeet Alase, David L Feder Designing feasible and qualitative methods for estimation of topological invariants, such as the Chern number, is of great significance for experimental realization of topological quantum matter. We first show that for fermionic or bosonic two-band systems supported on Bravais lattices with 2n-fold rotation symmetry, the Chern number (mod 2n) of one of the energy bands can be inferred from the pseudo-spin polarization of the band wavefunction at the high-symmetry crystal momenta in the Brillouin zone. We leverage this result to design an experimental scheme for ultracold atomic gases that uses Zeeman spectroscopy for validation of the topological phases with Chern number 2 on a triangular lattice. For bosons, this needs to be preceded by a timed Bloch oscillation. As part of the latter result, we present the first experimental scheme to our knowledge for simulating spin-orbit coupling on a triangular optical lattice. Our results highlight Bloch oscillations and Zeeman spectroscopy as robust tools for the detection of topological order, and also open doors to new experiments based on spin-orbit coupled systems beyond square lattices. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C27.00006: Hyperbolic band theory Joseph Maciejko, Steven Rayan The notions of Bloch wave, crystal momentum, and energy bands are commonly regarded as unique features of crystalline materials with commutative translation symmetries. Motivated by the recent realization of hyperbolic lattices in circuit QED, we exploit ideas from algebraic geometry to construct the first hyperbolic generalization of Bloch theory, despite the absence of commutative translation symmetries. For a quantum particle propagating in a large class of hyperbolic lattice potentials, we construct a continuous family of eigenstates that acquire Bloch-like phase factors under a discrete but noncommutative group of hyperbolic translations, the Fuchsian group of the lattice. A hyperbolic analog of crystal momentum arises as the set of Aharonov-Bohm phases threading the noncontractible cycles of a higher-genus Riemann surface naturally associated with this group. This crystal momentum lives in a higher-dimensional Brillouin zone torus, known in algebraic geometry as the Jacobian of the Riemann surface, and over which a discrete set of continuous energy bands can be computed. To illustrate the theory, we compute hyperbolic Bloch wavefunctions and bandstructures numerically for hyperbolic lattice potentials associated with a particular genus-2 Riemann surface, the Bolza surface. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C27.00007: Non-Hermitian band theory of nonreciprocal transmission and amplification Wen-Tan Xue, Mingrui Li, Yu-Min Hu, Fei Song, Zhong Wang The phenomenon of amplifying forward-propagating signals while blocking back-propagating ones, known as the directional or nonreciprocal amplification, is important for a wide range of applications. As open systems that exchange energy with the environment, directional amplifiers exhibit intrinsically non-Hermitian physics. General formulas for the gain and directionality, though highly desirable, have been lacking. These quantities are closely related to the Green's function whose general form has been unknown for non-Hermitan bands. In this work, we find these formulas in a compact and user-friendly form. This solution highlights intriguing connections between the directional amplification and non-Hermitian topological band theory. In particular, our formulas are based on the concept of generalized Brillouin zone, which was initially introduced as a key ingredient in understanding the non-Hermitian topology. These formulas could provide a widely applicable criterion for designing high-quality directional amplifiers, and point to new potential applications based on non-Hermitian band theory. |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C27.00008: Non-Hermitian Disorder-induced Topological Insulators Xiwang Luo, Chuanwei Zhang Recent studies of disorder or non-Hermiticity induced topological insulators |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C27.00009: Non-Hermitian Dynamics of Spin Chains with Loss and Gain Carlos Meriles, Rodolfo Hector Acosta, Pablo Zangara, Santiago Bussandri Mattia Understanding the joint dynamics of electron and nuclear spins is central to core concepts in solid-state magnetic resonance - such as spin-lattice relaxation and DNP - but a generalization that capitalizes on competing polarization loss and gain channels is still lacking. In this work, we theoretically study the non-Hermitian dynamics of hybrid electron/nuclear spin systems in the simultaneous presence of electron spin pumping and spin-lattice relaxation. We consider chain-like arrays where the nuclear spin coupling is mediated by pairs of interacting electron spins, one of which spin-polarizes under laser excitation. Setting an externally applied magnetic field to allow inter-electronic spin flips, we show that when the spin pumping rate reaches a critical threshold, nuclear spin polarization flows selectively in one direction but not in the other. The dynamics that ensues lead to asymmetric, site-selective nuclear spin polarization along the chain. In ring-like arrays, we identify a different final regime, featuring uniform polarization distributions and persistent nuclear spin currents, even in the absence of net nuclear polarization. Finally, we show that these processes can be made robust to defects in the chain through the periodic modulation of the applied magnetic field. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C27.00010: Correspondence between Winding Numbers and Skin Modes in Non-Hermitian Systems Kai Zhang, Zhesen Yang, Chen Fang We establish exact relations between the winding of “energy” (eigenvalue of Hamiltonian) on the complex plane as momentum traverses the Brillouin zone with periodic boundary condition, and the presence of “skin modes” with open boundary conditions in non-Hermitian systems. We show that the nonzero winding with respect to any complex reference energy leads to the presence of skin modes, and vice versa. We also show that both the nonzero winding and the presence of skin modes share the common physical origin that is the nonvanishing current through the system. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C27.00011: Non-Hermitian bulk-boundary correspondence and skin effect Yang Zhesen Recently, the conventional Bulk-boundary correspondence (BBC) is challenged in some non-Hermitian systems, e.g. the spectrum between open and periodic boundary conditions can be totally distinct [1]. In this talk, I will reveal the two-fold meaning of the non-Hermitian BBC [2]. On the one hand, the conventional boundary state is related to the wavefunction topology of the so-called generalized Brillouin zone (GBZ) Hamiltonian [1]; On the other hand, the non-Hermitian skin mode is related to the energy-spectra topology of the Bloch Hamiltonian [3]. An analytic method is introduced to calculate the GBZ exactly [2]. Finally, we will briefly discuss how to realize the non-Hermitian skin effect in condensed matter systems [4]. |
Monday, March 15, 2021 5:12PM - 5:48PM On Demand |
C27.00012: Topological photonics at the nanoscale Invited Speaker: Bo Zhen Novel concepts from topological physics have achieved great successes in optics and photonics. In this talk, I will present our recent results in designing new photonic devices based on the intuition of topological physics, and also exploring new topological phases using nonlinear optics. |
Monday, March 15, 2021 5:48PM - 6:00PM On Demand |
C27.00013: Enhanced repulsively and attractively bound atom pairs in topological optical lattice ladders Stuart Flannigan, Andrew Daley Inspired by the growing interest in using cold-atoms in optical lattices to explore the effects of strong interactions in topological band structures, we investigate phases in the Cruetz ladder and Lieb lattice which are both characterised by flat energy bands. By investigating realistic experimental implementations of the Creutz ladder, we understand how the lattice topology enhances the properties of interacting bound pairs giving rise to large pair-tunnelling which can lead to robust pair superfluidity. We also investigate fermions in a Lieb ladder at half filling where we show that pair correlations are also enhanced even when there is strong mixing with dispersive bands. We identify schemes for preparation of these phases via time-dependent parameter variation and look at ways to detect and characterise these systems in an experiment. This work provides a starting point for investigating the interplay between the effects of topology, interactions and pairing in more general systems, with potential future connections to quantum simulation of topological materials. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700