Signatures of Excited State Quantum Phase Transitions in Dissipative Quantum Systems

A quantum phase transition (QPT) refers to an abrupt change in the properties of a system's ground state as a control parameter crosses a critical value. An excited-state quantum phase transition (ESQPT) extends this concept to excited states, manifesting through features such as spectral kissing and divergences in the density of states. In this presentation, we demonstrate that these signatures of ESQPTs persist even in open quantum systems. Specifically, we show that analogous behaviors emerge in the steady states of a dissipative Kerr parametric oscillator, a platform experimentally realizable in superconducting circuits.