Formation and detection of a chiral orbital Bose liquid in an optical lattice

TL;DR

This paper investigates the thermal destruction of chiral superfluidity in p-orbital bosons within optical lattices, revealing an intermediate chiral Bose liquid phase and proposing a method to detect chiral order through lattice quench experiments.

Contribution

It uncovers the existence of a chiral Bose liquid phase caused by thermal fluctuations and proposes a novel detection method for chiral order in optical lattice experiments.

Findings

Thermal fluctuations induce a two-step transition destroying superfluidity.

An intermediate chiral Bose liquid phase with broken time-reversal symmetry exists.

A lattice quench can reveal chiral order through orbital oscillations.

Abstract

Recent experiments on $p$-orbital atomic bosons have suggested the emergence of a spectacular ultracold superfluid with staggered orbital currents in optical lattices. This raises fundamental questions like the effects of collective thermal fluctuations, and how to directly observe such chiral order. Here, we show via Monte Carlo simulations that thermal fluctuations destroy this superfluid in an unexpected two-step process, unveiling an intermediate normal phase with spontaneously broken time-reversal symmetry, dubbed "chiral Bose liquid". For integer fillings ($n\geq 2$) in the chiral Mott regime, thermal fluctuations are captured by an effective orbital Ising model, and Onsager's powerful exact solution is adopted to determine the transition from this intermediate liquid to the para-orbital normal phase at high temperature. A suitable lattice quench is designed to convert the staggered angular momentum, previously thought by experts difficult to directly probe, into coherent orbital oscillations, providing a smoking-gun signature of chiral order.