2019/08/30 by Carlos Sánchez Muñoz, Berislav Buca, Joseph Tindall +3 · 1 citation
Physics and Astronomy · #quant-ph #cond-mat.quant-gas #cond-mat.stat-mech
paper · pdf · doi:10.1103/physreva.100.042113
published as Phys. Rev. A 100, 042113 (2019)
arxiv created 2019/08/30 · arxiv updated 2019/10/23
In driven-dissipative systems, the presence of a strong symmetry guarantees the existence of several steady states belonging to different symmetry sectors. Here we show that, when a system with a strong symmetry is initialized in a quantum superposition involving several of these sectors, each individual stochastic trajectory will randomly select a single one of them and remain there for the rest of the evolution. Since a strong symmetry implies a conservation law for the corresponding symmetry operator on the ensemble level, this selection of a single sector from an initial superposition entails a breakdown of this conservation law at the level of individual realizations. Given that such a superposition is impossible in a classical, stochastic trajectory, this is a a purely quantum effect with no classical analogue. Our results show that a system with a closed Liouvillian gap may exhibit, when monitored over a single run of an experiment, a behaviour completely opposite to the usual notion of dynamical phase coexistence and intermittency, which are typically considered hallmarks of a dissipative phase transition. We discuss our results with a simple, realistic model of squeezed superradiance.