Experimental demonstration of coherence flow in $\mathcal{PT}$- and anti-$\mathcal{PT}$-symmetric systems

TL;DR

This paper experimentally investigates coherence flow in $ ext{PT}$- and $ ext{APT}$-symmetric quantum systems, revealing distinct oscillation patterns and coherence backflows, advancing understanding of quantum coherence dynamics in non-Hermitian systems.

Contribution

It provides the first experimental demonstration of coherence flow behaviors in $ ext{PT}$- and $ ext{APT}$-symmetric systems, including coherence backflows and stable coherence values, supported by analytic proofs.

Findings

Observation of periodic coherence oscillations in symmetry unbroken regime

Identification of two coherence backflows in $ ext{PT}$-symmetric systems

Detection of stable coherence flow in symmetry broken regime

Abstract

Non-Hermitian parity-time ($\mathcal{PT}$) and anti-parity-time ($\mathcal{APT}$)-symmetric systems exhibit novel quantum properties and have attracted increasing interest. Although many counterintuitive phenomena in $\mathcal{PT}$- and $\mathcal{APT}$-symmetric systems were previously studied, coherence flow has been rarely investigated. Here, we experimentally demonstrate single-qubit coherence flow in $\mathcal{PT}$- and $\mathcal{APT}$-symmetric systems using an optical setup. In the symmetry unbroken regime, we observe different periodic oscillations of coherence. Particularly, we observe two complete coherence backflows in one period in the $\mathcal{PT}$-symmetric system, while only one backflow in the $\mathcal{APT}$-symmetric system. Moreover, in the symmetry broken regime, we observe the phenomenon of stable value of coherence flow. We derive the analytic proofs of these phenomena and show that most experimental data agree with theoretical results within one standard deviation. This work opens avenues for future study on the dynamics of coherence in $\mathcal{PT}$- and $\mathcal{APT}$-symmetric systems.