Probing phase transitions in non-Hermitian systems with Multiple Quantum Coherences

TL;DR

This paper demonstrates that multiple quantum coherences (MQCs) can effectively probe various equilibrium phase transitions in non-Hermitian quantum systems, revealing critical phenomena and spectral features.

Contribution

It introduces the use of MQCs as a tool to detect phase transitions in non-Hermitian systems, connecting quantum coherence measures with critical points and spectral properties.

Findings

MQCs witness parity-symmetry breaking in two-level systems.

MQCs capture the Yang-Lee phase transition in the non-Hermitian transverse field Ising model.

MQCs identify mobility edges and topological transitions in the Hatano-Nelson model.

Abstract

Understanding the interplay between quantum coherence and non-Hermitian features would enable the devising of quantum technologies based on dissipative systems. In turn, quantum coherence can be characterized in terms of the language of multiple quantum coherences (MQCs) originally developed in solid-state nuclear magnetic resonance (NMR), nowadays applied to the detection of quantum chaos, and to the study of criticality in many-body quantum systems. Here we show the usefulness of MQCs for probing equilibrium phase transitions in non-Hermitian systems. To do so, we investigate the connection of quantum coherences and critical points for several paradigmatic non-Hermitian Hamiltonians. For a non-Hermitian two-level system, MQCs witness the parity-symmetry breaking phase transition from the unbroken to the broken phase. Furthermore, for the non-Hermitian transverse field Ising model, MQCs capture the Yang-Lee phase transition in which the ground state energy acquires a nonzero imaginary component. For the disordered Hatano-Nelson (HN) model with periodic boundary conditions, MQCs testify the emergence of mobility edges in the spectrum of this model. In addition, MQCs signal the topological phase transition exhibited by the complex energy spectra of the disorder-free HN model. Finally, we comment on experimentally probing phase transitions in NMR systems realizing non-Hermitian Hamiltonians. Our results have applications to non-Hermitian quantum sensing, quantum thermodynamics, and in the study of the non-Hermitian skin effect.