Model study of dissipation in quantum phase transitions

TL;DR

This paper investigates how dissipation affects quantum phase transitions in a spin system coupled to a bosonic bath, revealing changes in phase diagram, excitations, and entanglement properties.

Contribution

It introduces a model combining an infinite-range transverse Ising system with a bosonic bath and analyzes its phase diagram and excitations, highlighting the effects of dissipation.

Findings

Phase diagram depends on bath coupling and magnetic field.

Quantum critical point features a vanishing energy gap.

Increasing bath coupling leads to spin entanglement loss.

Abstract

We consider a prototypical system of an infinite range transverse field Ising model coupled to a bosonic bath. By integrating out the bosonic degrees, an effective anisotropic Heisenberg model is obtained for the spin system. The phase diagram of the latter is calculated as a function of coupling to the heat bath and the transverse magnetic field. Collective excitations at low temeratures are assessed within a spin-wave like analysis that exhibits a vanishing energy gap at the quantum critical point. We also consider another limit where the system reduces to a generalized spin-boson model of two interacting spins. By increasing the coupling strength with the heat bath, the two-spin wavefunction changes from an entangled state to a factorized state of two spins which are aligned along the transverse field. We also discuss the possible realization and application of the model to different physical systems.