Quantum phase transition of nonlinear light in the finite size Dicke Hamiltonian

TL;DR

This paper investigates quantum phase transitions in a finite-size Dicke model with nonlinear interactions, deriving critical points and analyzing entanglement and squeezing phenomena in the system.

Contribution

It provides analytical expressions for critical couplings and ground states, and explores entanglement and squeezing in a finite-size nonlinear light-matter system.

Findings

Analytical critical coupling values derived for different regimes

Bipartite entanglement observed between atoms and photons

Coexistence of squeezed fields and atomic ensembles

Abstract

We study the quantum phase transition of a N two-level atomic ensemble interacting with an optical degenerate parametric process, which can be described by the finite size Dicke Hamiltonian plus counter-rotating and quadratic field terms. Analytical closed forms of the critical coupling value and their corresponding separable ground states are derived in the weak and strong coupling regimes. The existence of bipartite entanglement between the two-level-system ensemble and photon field as well as between ensemble components for moderate coupling is shown through numerical analysis. Given a finite size, our results also indicate the co-existence of squeezed fields and squeezed atomic ensembles.