Dynamic magnetization in non-Hermitian quantum spin system

TL;DR

This paper explores how non-Hermiticity influences magnetization dynamics in quantum spin chains, revealing high-order exceptional points, state convergence to ground states, and hysteresis behavior driven by complex local fields.

Contribution

It introduces the creation of high-order exceptional points and demonstrates magnetization switching driven by non-Hermitian effects in quantum spin systems.

Findings

High-order exceptional points up to (N+1)-level coalescence.

Final states approach the ground state regardless of initial conditions.

Hysteresis loop in magnetization driven by non-Hermiticity.

Abstract

We report a global effect induced by the local complex field, associated with the spin-exchange interaction. High-order exceptional point up to ($N+1$)-level coalescence is created at the critical local complex field applied to the $N$-size quantum spin chain. The ($N+1$)-order coalescent level is a saturated ferromagnetic ground state in the isotropic spin system. Remarkably, the final state always approaches the ground state for an arbitrary initial state with any number of spin flips; even if the initial state is orthogonal to the ground state. Furthermore, the switch of macroscopic magnetization is solely driven by the time and forms a hysteresis loop in the time domain. The retentivity and coercivity of the hysteresis loop mainly rely on the non-Hermiticity. Our findings highlight the cooperation of non-Hermiticity and the interaction in quantum spin system, suggest a dynamical framework to realize magnetization, and thus pave the way for the non-Hermitian quantum spin system.