Phases, instabilities and excitations in a two-component lattice model with photon-mediated interactions

TL;DR

This paper explores the complex phase diagram and excitations of a two-component spin Bose-Hubbard model with photon-mediated interactions, revealing rich phases including superfluid, insulating, and antiferromagnetic states, relevant for cold-atom experiments.

Contribution

It provides a comprehensive analysis of the phase diagram and low-energy excitations of a two-component lattice model with photon-mediated interactions, highlighting novel magnetic and instability phenomena.

Findings

Rich phase diagram with superfluid and insulating phases

Antiferromagnetic order at small spin-dependent coupling

Presence of tunable spin-exchange excitations

Abstract

Engineering long-range interacting spin systems with ultra cold atoms offers the possibility to explore exotic magnetically ordered phases in strongly-correlated scenarios. Quantum gases in optical cavities provide a versatile experimental platform to further engineer photon-mediated interactions and access the underlying microscopic processes by probing the cavity field. Here, we study a two-component spin Bose-Hubbard system with cavity-mediated interactions. We provide a comprehensive overview of its phase diagram and transitions in experimentally relevant regimes. The interplay of different energy scales yields a rich phase diagram with superfluid and insulating phases exhibiting density modulation or spin ordering. In particular, the combined effect of contact and global-range interactions gives rise to an antiferromagnetically ordered phase for arbitrarily small spin-dependent light-matter coupling, while long-range and inter-spin contact interactions introduce regions of instability and phase separation in the phase diagram. We further study the low energy excitations above the antiferrogmagnetic phase. Besides particle-hole branches, it hosts spin-exchange excitations with a tunable energy gap. The studied lattice model can be readily realized in cold-atom experiments with optical cavities.