Experimental demonstration of coherence flow in PT- and anti-PT-symmetric systems

Yu-Liang Fang,Yu Zhang,Dong-Xu Chen,Chui-Ping Yang,Franco Nori,Jun-Long Zhao,Qi-Cheng Wu,Yan-Hui Zhou

doi:10.1038/s42005-021-00728-8

Abstract

Non-Hermitian parity-time ({{{{{{{mathcal{P}}}}}}}}{{{{{{{mathcal{T}}}}}}}}) and anti-parity-time ({{{{{{{mathcal{APT}}}}}}}})-symmetric systems exhibit novel quantum properties and have attracted increasing interest. Although many counterintuitive phenomena in {{{{{{{mathcal{P}}}}}}}}{{{{{{{mathcal{T}}}}}}}}- and {{{{{{{mathcal{APT}}}}}}}}-symmetric systems were previously studied, coherence flow has been rarely investigated. Here, we experimentally demonstrate single-qubit coherence flow in {{{{{{{mathcal{P}}}}}}}}{{{{{{{mathcal{T}}}}}}}}- 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{P}}}}}}}}{{{{{{{mathcal{T}}}}}}}}-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{P}}}}}}}}{{{{{{{mathcal{T}}}}}}}}- and {{{{{{{mathcal{APT}}}}}}}}-symmetric systems.

Highlights

Non-Hermitian parity-time (PT ) and anti-parity-time (APT )-symmetric systems exhibit novel quantum properties and have attracted increasing interest
The Double touch of coherence (DTC) phenomenon in one period in the PT -symmetric unbroken regime has been demonstrated, which does not occur in the APT -symmetric system
The phenomenon of stable value (PSV) has been observed in the PT /APT -symmetric broken regime, which is independent of the initial state

Summary

Introduction

Non-Hermitian parity-time (PT ) and anti-parity-time (APT )-symmetric systems exhibit novel quantum properties and have attracted increasing interest. Recent experiments have observed the following: information flow in PT -symmetric systems[23], protection of quantum coherence in a PT -broken superconducting circuit[36], EP-enhanced coherence and oscillation of coherence in a single-ion PT -symmetry system[37], entanglement restoration in a PT -symmetric system using a universal circuit[38], and dynamical features of a triple-qubit system in which one qubit evolves under a local PT -symmetric Hamiltonian[39]. Another important counterpart, anti-PT (APT ) symmetry, has recently attracted considerable interest. In Hermitian quantum systems isolated from their environment, the coherence flow between the subsystems generally oscillates periodically over time and the oscillation period depends on the coupling strength between the subsystems

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Results

Discussion

Conclusion