Dynamics of the rotated Dicke model

TL;DR

This paper investigates how rotating the collective spin in the Dicke model affects quantum criticality, revealing a shift in the critical point and a reentrant phase transition, enabling probing of quantum phase transitions without crossing the critical surface.

Contribution

It introduces a method to study quantum criticality by rotating the spin, shifting the critical point without crossing it, and uncovers a non-equilibrium reentrant phase transition in the driven model.

Findings

Quantum critical point shifts with rotation velocity.

Reentrant quantum critical behavior observed.

Non-equilibrium phase diagram constructed.

Abstract

We study quantum dynamics of the rotationally driven Dicke model where the collective spin is rotated around the z axis with a finite velocity. In the absence of the rotating wave approximation we observe that for several physically relevant initial states the position of the quantum critical point is shifted by the amount given by the applied rotation velocity. This allows us to probe the quantum criticality "from a distance" in parameter space without actual crossing of the quantum critical surface but instead by encircling it in the parameter space. This may provide a useful experimental hint since the quantum state is not destroyed by this protocol. Moreover, for the coherent initial state we observe an interesting non-equilibrium reentrant phenomenon of quantum critical behavior as a function of the driving velocity and construct a non-equilibrium phase diagram of the driven model.