Revealing the nature of nonequilibrium phase transitions with quantum trajectories

: Link V, Luoma K, Strunz WT

Publisher: AMER PHYSICAL SOC

: 2019

: Physical Review A

: PHYSICAL REVIEW A

: PHYS REV A

: ARTN 062120

: 99

: 6

: 7

: 2469-9926

DOI: https://doi.org/10.1103/PhysRevA.99.062120

A damped and driven collective spin system is analyzed by using quantum state diffusion. This approach allows for a mostly analytical treatment of the investigated nonequilibrium quantum many-body dynamics, which features a phase transition in the thermodynamical limit. The exact results obtained in this work, which are free of any finite-size defects, provide a complete understanding of the model. Moreover, the trajectory framework gives an intuitive picture of the two phases occurring, revealing a spontaneously broken symmetry and allowing for a qualitative and quantitative characterization of the phases. We determine exact critical exponents, investigate finite-size scaling, and explain a remarkable nonalgebraic behavior at the transition in terms of torus hopping.