Quantum phases of mixtures of atoms and molecules on optical lattices

TL;DR

This paper explores the phase diagram of a two-species Bose-Hubbard model with conversion, revealing phenomena like population inversion and a unique Super-Mott phase through Quantum Monte Carlo simulations.

Contribution

It provides the first exact quantum Monte Carlo analysis of a two-species Bose-Hubbard model with conversion, identifying novel phases and population dynamics.

Findings

Inversion of population where the second species dominates

Existence of a Super-Mott phase with superfluidity without supercurrent

Two detailed phase diagrams in different parameter planes

Abstract

We investigate the phase diagram of a two-species Bose-Hubbard model including a conversion term, by which two particles from the first species can be converted into one particle of the second species, and vice-versa. The model can be related to ultra-cold atom experiments in which a Feshbach resonance produces long-lived bound states viewed as diatomic molecules. The model is solved exactly by means of Quantum Monte Carlo simulations. We show than an "inversion of population" occurs, depending on the parameters, where the second species becomes more numerous than the first species. The model also exhibits an exotic incompressible "Super-Mott" phase where the particles from both species can flow with signs of superfluidity, but without global supercurrent. We present two phase diagrams, one in the (chemical potential, conversion) plane, the other in the (chemical potential, detuning) plane.