Robustness of entanglement in a non-Hermitian cavity-optomechanical system even away from exceptional points

TL;DR

This paper explores the behavior of entanglement in non-Hermitian, $ ext{PT}$-symmetric optomechanical systems, revealing that entanglement revival and mitigation of sudden death are possible even away from exceptional points, with implications for quantum device development.

Contribution

It demonstrates that beneficial entanglement dynamics occur in non-Hermitian systems outside of exceptional points, expanding the experimental and theoretical understanding of such systems.

Findings

Entanglement revival is robust away from EPs.

Sudden death of entanglement can be mitigated at EPs.

Thermal noise has limited impact on entanglement revival.

Abstract

Quantum physics can be extended into the complex domain by considering non-Hermitian Hamiltonians that are $\mathcal{PT}$-symmetric. These exhibit exceptional points (EPs) where the eigenspectrum changes from purely real to purely imaginary values and have useful properties enabling applications such as accelerated entanglement generation and the delay of the sudden death of entanglement in noisy systems. An interesting question is whether similar beneficial effects can be achieved away from EPs, since this would extend the available parameter space and make experiments more accessible. We investigate this by considering a $\mathcal{PT}$-symmetric optomechanical system but also consider what happens when two-mode squeezing interactions are included, taking us into the pseudo-Hermitian regime. The addition of squeezing is motivated by an attempt to extend the lifetime of the system's entanglement. While this does not prove to be the case, rich dynamics are nonetheless observed in both the pseudo-Hermitian and $\mathcal{PT}$-symmetric systems, including the sudden death and revival of entanglement under certain conditions. In both cases, we find that the sudden disappearance of entanglement can be mitigated at EPs, and also show that the revival of entanglement is quite robust to thermal noise in a group of parameters away from the EPs. This investigation extends our understanding of non-Hermitian systems and opens a new perspective for the development of quantum devices in non-Hermitian systems even away from EPs.