Ladder of Loschmidt anomalies in the deep strong-coupling regime of a qubit-oscillator system

Abstract

We uncover a remarkably regular array of singularitylike structures within the deep strong-coupling limit of qubit-oscillator (e.g., light-matter) systems described by the quantum Rabi model as a function of time and coupling strength. These nonanalytic anomalies in the Loschmidt amplitude (echoes) suggest the existence of new forms of dynamical phase transition within this deep strong-coupling regime. The key feature whereby the initial state collapses into orthogonal states at select values of the interaction strength and select times may be used to enhance---or attack---quantum information processing or computation schemes that rely on removing---or retaining---a given quantum state.