Synthetic gauge field in two interacting ultracold atomic gases without an optical lattice

TL;DR

This paper demonstrates the creation of a synthetic gauge field in a two-component ultracold atomic gas system without using an optical lattice, revealing topological properties and edge states through Floquet engineering.

Contribution

It introduces a method to generate a synthetic gauge field in a two-mode quantum gas system via periodic driving, connecting quantum gases with topological condensed matter phenomena.

Findings

Observation of Hofstadter butterfly pattern in the quasienergy spectrum

Identification of non-trivial topological edge states

Detection of chiral edge state dynamics and effects of nonlinear interactions

Abstract

A 2D Fock-state lattice (FSL is constructed from the many-body states of two interacting two-mode quantum gases. By periodically driving the interspecies interactions and pulsing the tunneling between the two modes of each gas, a synthetic gauge field is generated. We derive an effective Hamiltonian in the short pulse limit which resembles the Harper-Hofstadter Hamiltonian where the magnetic flux per plaquette is controlled by the ratio of the interaction energy and the driving frequency. The quasispectrum of the Floquet operator of the driving sequence shows the celebrated Hofstadter's butterfly pattern as well as the existence of edge states. From the calculation of the local Chern marker, we establish that the FSL has non-trivial topology and by simulating the dynamics of the edge states, show that they exhibit chirality. Finally, the inclusion of the intraspecies interactions creates an overall harmonic trap in the lattice and introduces the nonlinear effect of macroscopic quantum self-trapping which is shown to hinder the movement along the edge of the lattice. This work introduces a new avenue to explore synthetic gauge fields and provides a link between non-trivial condensed matter systems and quantum gases.