Quantum Phases of Ultracold Bosonic Atoms in two Bands of an Optical-Lattice coupled by a Cavity Field

TL;DR

This paper investigates quantum phase transitions in ultracold bosonic atoms across two bands of an optical lattice coupled by a cavity field, revealing how cavity-mediated interactions influence superfluid and Mott insulator phases.

Contribution

It introduces a model of two-band ultracold bosons coupled via a cavity mode, showing how this coupling alters phase boundaries and enables novel coexistence phases.

Findings

Cavity coupling shifts Mott insulator regions to higher lattice depths.

Photon-assisted tunneling enhances atomic coherence across bands.

Coexistence of Mott insulator in one band and superfluid in the other predicted.

Abstract

We study the quantum phase transitions between superfluid and Mott insulator states for ultracold bosons occupying two bands of an optical lattice. The two atomic states are resonantly coupled by a single cavity mode which mediates transitions between the two bosonic particle modes via absorption or emission of a cavity photon. This coupling between the bands shifts the appearance of the Mott insulator phase towards deeper optical lattice potentials and stronger on-site interaction strength, as atomic coherence can build up via photon assisted tunneling in both bands. Varying the intra and interband on-site interactions leads to several different atomic phase configurations. There are even parameter regions where a mean field approach predicts concurrence of a Mott insulator state in one band, while atoms in the second band stay superfluid.