Transverse Spin Dynamics in the Anisotropic Heisenberg Model Realized with Ultracold Atoms

Paul Niklas Jepsen,Ivana Dimitrova,Jesse Amato-Grill,Wen Wei Ho,Eugene Demler,Wolfgang Ketterle

doi:10.1103/physrevx.11.041054

Abstract

In Heisenberg models with exchange anisotropy, transverse spin components are not conserved and can decay not only by transport, but also by dephasing. Here, we utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin chains and observe fast, local spin decay controlled by the anisotropy. However, even for isotropic interactions, we observe dephasing due to a new effect: an effective magnetic field created by superexchange. If spatially uniform, it leads only to uniform spin precession and is, therefore, typically ignored. However, we show through experimental studies and extensive numerical simulations how this superexchange-generated field is relevant and leads to additional dephasing mechanisms over the exchange anisotropy: There is dephasing due to (i) inhomogeneity of the effective field from variations of lattice depth between chains; (ii) a twofold reduction of the field at the edges of finite chains; and (iii) fluctuations of the effective field due to the presence of mobile holes in the system. The latter is a new coupling mechanism between holes and magnons. All these dephasing mechanisms have not been observed before with ultracold atoms and illustrate basic properties of the underlying Hubbard model.3 MoreReceived 14 March 2021Accepted 23 August 2021DOI:https://doi.org/10.1103/PhysRevX.11.041054Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCold gases in optical latticesQuantum quenchQuantum simulationSpin dynamicsSpin relaxationAtomic, Molecular & Optical

Highlights

The famous Heisenberg Hamiltonian, called the Heisenberg–Dirac–van Vleck Hamiltonian [1,2,3], describes localized particles on a lattice interacting via spin-exchange couplings
We utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin chains and observe fast, local spin decay controlled by the anisotropy
We focus here on two paradigmatic models, which represent complementary spin physics: the XX model, which has only transverse spin-spin couplings and can be mapped to a noninteracting system of fermions, and the XXX model, which has isotropic spin couplings

Summary

Introduction

The famous Heisenberg Hamiltonian, called the Heisenberg–Dirac–van Vleck Hamiltonian [1,2,3], describes localized particles on a lattice interacting via spin-exchange couplings. It serves as a paradigmatic model for a host of emergent phenomena, such as ferromagnetism (due to Coulomb exchange, called potential or direct exchange), antiferromagnetism (due to kinetic exchange from tunneling, called superexchange) [4], and spin-glass physics [5], as well as exotic states of matter like topologically ordered quantum spin liquids [6]. The dynamics of such models is very rich and multifaceted and is under active, intense investigation. The interplay of spontaneous symmetry breaking can lead to long-lived, metastable, prethermal states in addition to the onset of regular spin diffusion [14,15,16] or even turbulent relaxation with universal scaling of spin-spin correlations [17]

Methods

Results

Conclusion