Stable states with nonzero entropy under broken PT symmetry

The PT-symmetric non-Hermitian systems have been widely studied and explored both in theory and in experiment due to their various interesting features. In this work we focus on the dynamical features of a triple-qubit system, one of which evolves under a local PT-symmetric Hamiltonian. An abnormal dynamic pattern in the entropy evolution process is identified that presents a parameter-dependent stable state, determined by the non-Hermiticity of Hamiltonian in the broken phase of PT symmetry. The entanglement and mutual information of a two-body subsystem can increase beyond the initial values, which do not exist in the Hermitian and two-qubit PT-symmetric systems. Moreover, an experimental demonstration of the stable states in non-Hermitian systems with nonzero entropy and entanglement is realized on a four-qubit quantum simulator with nuclear spins. Our work reveals the distinctive dynamic features in the triple-qubit PT-symmetric system and paves the way for practical quantum simulation of multiparty non-Hermitian system on quantum computers.