arXiv2021
Coupling a system to a nonthermal environment can profoundly affect the phase diagram of the closed system, giving rise to a special class of dissipation-induced phase transitions. Such transitions take the system out of its ground state and stabilize a higher-energy stationary state, rendering it the sole attractor of the dissipative dynamics. In this work, we present a unifying methodology, which we use to characterize this ubiquitous phenomenology and its implications for the open system dynamics. Specifically, we analyze the closed system's phase diagram, including symmetry-broken phases, and explore their corresponding excitations' spectra. Opening the system, the environment can overwhelm the system's symmetry-breaking tendencies, and changes its order parameter. As a result, isolated distinct phases of similar order become connected, and new phase-costability regions appear. Interestingly, the excitations differ in the newly-connected regions through a change in their symplectic norm, which is robust to the introduction of dissipation. As a result, by tuning the system from one phase to the other across the dissipation-stabilized region, the open system fluctuations exhibit an exceptional point-like scenario, where the fluctuations become overdamped, only to reappear with an opposite sign in the dynamical response function of the system. The overdamped region is also associated with squeezing of the fluctuations. We demonstrate the pervasive nature of such dissipation-induced phenomena in two prominent examples, namely in parametric resonators and in light-matter systems. Our work draws a crucial distinction between quantum phase transitions and their zero-temperature open system counterparts.