Double symmetry breaking and 2D quantum phase diagram in spin-boson systems

TL;DR

This paper explores the phase diagram of two spin chains interacting with a common bosonic field, revealing double symmetry breaking and a four-phase structure with potential for manipulation via Berry effects.

Contribution

It introduces a theoretical model of two independent spin chains coupled to a bosonic field, uncovering a novel four-phase diagram with double symmetry breaking and degeneracy.

Findings

Identification of four distinct phases in the ($,$) plane.

Demonstration of symmetry breaking and degeneracy in the ground state.

Potential for manipulation using non-abelian Berry effects.

Abstract

The quantum ground state properties of two independent chains of spins (two-levels systems) interacting with the same bosonic field are theoretically investigated. Each chain is coupled to a different quadrature of the field, leading to two independent symmetry breakings for increasing values of the two spin-boson interaction constants $\Omega_C$ and $\Omega_I$. A phase diagram is provided in the plane ($\Omega_C$,$\Omega_I$) with 4 different phases that can be characterized by the complex bosonic coherence of the ground states and can be manipulated via non-abelian Berry effects. In particular, when $\Omega_C$ and $\Omega_I$ are both larger than two critical values, the fundamental subspace has a four-fold degeneracy. Possible implementations in superconducting or atomic systems are discussed.