Hidden exceptional point, localization-delocalization phase transition in Hermitian bosonic Kitaev model

Abstract: Exceptional points (EPs), a unique feature of non-Hermitian systems, represent degeneracies in non-Hermitian operators that likely do not occur in Hermitian systems. Nevertheless, unlike its fermionic counterpart, a Hermitian bosonic Kitaev model supports a non-Hermitian core matrix, involving a quantum phase transition (QPT) when an exceptional point appears. In this study, we examine QPTs by mapping the Hamiltonian onto a set of equivalent single-particle systems using a Bardeen-Cooper-Schrieffer (BCS)-like pairing basis. We demonstrate the connection between the hidden EP and the localization-delocalization transition in the equivalent systems. The result is applicable to a Dicke model, which allows the experimental detection of the transition based on the measurement of the average number of photons for the quench dynamics stating from the empty state. Numerical simulations of the time evolution reveal a clear transition point at the EP.