Excitation spectra of strongly correlated lattice bosons and polaritons

TL;DR

This paper investigates the spectral properties of strongly correlated lattice bosons and polaritons near the Mott insulator to superfluid transition using quantum Monte Carlo simulations, revealing additional gapped modes and emergent symmetries.

Contribution

It provides a comparative analysis of the Bose-Hubbard and polariton models, highlighting spectral features, emergent symmetries, and critical exponents near the phase transition.

Findings

Presence of additional gapped modes in the superfluid phase spectra

Emergent particle-hole symmetry near the Mott lobe tip in the polariton model

Mean field critical exponents consistent with field theory predictions

Abstract

Spectral properties of the Bose-Hubbard model and a recently proposed coupled-cavity model are studied by means of quantum Monte Carlo simulations in one dimension. Both models exhibit a quantum phase transition from a Mott insulator to a superfluid phase. The dynamic structure factor $S(k,\omega)$ and the single-particle spectrum $A(k,\omega)$ are calculated, focusing on the parameter region around the phase transition from the Mott insulator with density one to the superfluid phase, where correlations are important. The strongly interacting nature of the superfluid phase manifests itself in terms of additional gapped modes in the spectra. Comparison is made to recent analytical work on the Bose-Hubbard model. Despite some subtle differences due to the polaritonic particles in the cavity model, the gross features are found to be very similar to the Bose-Hubbard case. For the polariton model, emergent particle-hole symmetry near the Mott lobe tip is demonstrated, and temperature and detuning effects are analyzed. A scaling analysis for the generic transition suggests mean field exponents, in accordance with field theory results.