Quantum emulsion: a glassy phase of bosonic mixtures in optical lattices

TL;DR

This paper explores a novel glassy phase in bosonic mixtures within optical lattices, revealing a complex landscape of metastable states that resemble emulsions and exhibit Bose glass properties, with a transition to superfluidity controllable via Feshbach resonance.

Contribution

It introduces the concept of quantum emulsion states in bosonic mixtures, showing their glassy, metastable nature and connection to Bose glass behavior, and demonstrates a quantum phase transition to superfluidity.

Findings

Existence of metastable quantum emulsion states with glassy properties

Finite compressibility without superfluidity in these states

Tuning interactions induces a quantum phase transition to superfluidity

Abstract

We numerically investigate mixtures of two interacting bosonic species with unequal parameters in one-dimensional optical lattices. In large parameter regions full phase segregation is seen to minimize the energy of the system, but the true ground state is masked by an exponentially large number of metastable states characterized by microscopic phase separation. The ensemble of these quantum emulsion states, reminiscent of emulsions of immiscible fluids, has macroscopic properties analogous to those of a Bose glass, namely a finite compressibility in absence of superfluidity. Their metastability is probed by extensive quantum Monte Carlo simulations generating a rich correlated stochastic dynamics. The tuning of the repulsion of one of the two species via a Feshbach resonance drives the system through a quantum phase transition to the superfluid state.