Third-Order Exceptional Point in Non-Hermitian Spin-Orbit-Coupled cold atoms

TL;DR

This paper reports the discovery of a third-order exceptional point (EP3) in a non-Hermitian, spin-orbit-coupled cold atom system, revealing enhanced sensitivity and unique dynamical behaviors compared to second-order EPs.

Contribution

It introduces a PT-symmetry protected three-level non-Hermitian system with EP3 in dissipative spin-orbit-coupled fermions, and explores its band structure, sensitivity, and dynamical encircling behaviors.

Findings

EP3 exhibits cubic-root energy dispersion and enhanced sensitivity.

EP2 with square-root dispersion is also analyzed, showing symmetry dependence.

Distinct adiabatic and nonadiabatic encircling behaviors for EP3 compared to EP2.

Abstract

Exceptional points (EPs) has seen substantial advances in both experiment and theory. However, in quantum systems, higher-order exceptional points remain of great interest and possess numerous intriguing properties yet to be fully explored. Here, we describe a \emph{PT} symmetry-protected three-level non-Hermitian system with the dissipative spin-orbit-coupled (SOC) fermions in which a third-order exceptional point (EP3) emerges when both the eigenvalues and eigenstates of the system collapse into one. The band structure and its spin dynamics are explored for $^{173}$Yb fermions. We highlight the enhanced sensitivity to the external perturbation of EP3 with cubic-root energy dispersion. Additionally, we investigate the second-order exceptional point (EP2) with square-root energy dispersion in a three-level quantum system with the absence of parity symmetry, which proves that the enhanced sensitivity closely relates to the symmetries of the NH system. Furthermore, we analyze the encircling behavior of EP3 in terms of the adiabatic limit and the nonadiabatic dynamics and discover some different results from that of EP2.