Quantum Correlations in the XY Model Under a Non-Uniform Imaginary Magnetic Field

Abstract

In non-Hermitian spin chain systems, spontaneous symmetry breaking induced by non-Hermiticity leads to significant differences in the behavior of quantum correlations compared to Hermitian quantum systems. This paper discusses the manipulation of quantum correlations in the Heisenberg XY spin chain model under an imaginary magnetic field. Based on the energy spectrum structure of the non-Hermitian spin chain system obtained in the biorthogonal basis, we analyzed the efficiency of nonuniform imaginary magnetic fields in the generation and dynamical control of quantum correlations. The results indicate that non-Hermitian spin chain systems subjected to uniform or nonuniform imaginary magnetic fields exhibit superior entanglement properties compared to systems under transverse real fields. In particular, when the PT-symmetry in the system is unbroken, the imaginary magnetic field monotonically enhances the thermal entanglement of the system. We observed entanglement sudden ‘death’ and ‘revival’ phenomena in the PT-symmetric region under a nonuniform imaginary magnetic field. In the PT-symmetry broken region, entanglement is enhanced further due to the presence of exceptional points. Moreover, the time evolution of quantum entanglement and quantum discord reveals that the system transitions from the unbroken PT-symmetric region to the broken region as the imaginary magnetic field increases. In this process, the periodic oscillatory patterns of quantum correlations change to a monotonically increasing behavior, eventually converging to a steady-state value. Our results provide a theoretical basis for using imaginary magnetic fields for controlling quantum correlations and offer a strategy for achieving maximally entangled states in non-Hermitian spin chain systems.