Chiral state transfer under dephasing

TL;DR

This paper investigates how dephasing affects chiral state transfer around exceptional points in non-Hermitian systems, revealing that decoherence suppresses adiabatic transfer but allows chirality at intermediate times, with implications for experimental control.

Contribution

It introduces a full Lindblad master equation analysis of dephasing effects on chiral state transfer, highlighting the emergence of gaps in the Liouvillian spectrum and the conditions for chirality restoration.

Findings

Dephasing introduces gaps in the Liouvillian eigenspectrum.

Adiabatic chiral transfer is suppressed by dephasing.

Chirality can be restored at intermediate encircling times.

Abstract

Exceptional points emerge in the complex eigenspecra of non-Hermitian systems, and give rise to rich critical behaviors. An outstanding example is the chiral state transfer, where states can swap under an adiabatic encircling around the exceptional point, but only along one direction. In dissipative quantum systems, such exceptional-point encirclings are often accompanied by decoherence, whose impact is beyond the description of non-Hermitian Hamiltonians. In this work, we study in detail the effects of dephasing on the encircling dynamics, adopting the full Lindblad master equation. Introducing experimentally relevant quantum-jump processes that account for dephasing, we show that gaps emerge in the eigenspectra landscape of the corresponding Liouvillian superoperator. It follows that the chiral state transfer does not take place in the adiabatic limit, since the system always adiabatically follows the quasi-steady state of the Liouvillian regardless of the encircling direction. Nevertheless, the chirality is restored at intermediate encircling times, where the dynamics is non-adiabatic in both encircling directions, distinct from the typical chiral state transfer in non-Hermitian systems. While our results are applicable to several recent experiments, we examine a recent cold-atom experiment in particular, and show that the observed long-time chirality is but limited to the special encircling path therein. Our study provides further insight into the chiral state transfer under experimental conditions, and is helpful for controlling open-system dynamics from the perspective of non-Hermitian physics.