Parameter estimation and quantum entanglement in PT symmetrical cavity magnonics system

TL;DR

This paper explores parameter estimation and quantum entanglement in a PT symmetrical magnon-cavity system, revealing optimal measurement conditions and the impact of quantum fluctuations on entanglement.

Contribution

It introduces a method to analyze parameter estimation in PT symmetrical magnon systems and identifies optimal measurement strategies and the effects of quantum fluctuations.

Findings

Optimal estimation does not occur at the exceptional point due to quantum fluctuations.

Measurements at the exceptional point become more optimal with increased measurement time.

Direct photon detection is optimal for initial vacuum states.

Abstract

We investigate the parameter estimation in a magnon-cavity-magnon coupled system. PT symmetrical two magnons system can be formed in the gain magnetic materials by the adiabatic elimination of the cavity field mode. We show that the optimal estimation will not appear at the exceptional point due to that the quantum fluctuations are the strongest at the exceptional point. Moreover, we demonstrate that the measurements at the exceptional point tend to be optimal with the increase of prepared time. And the direct photon detection is the optimal measurement for the initial state in the vacuum input state. For the open PT symmetrical two magnons system, the quantum fluctuations will greatly reduce the degree of entanglement. Finally, we show that a higher estimated magnetic sensitivity can be obtained by measuring the frequency of one magnon in the PT symmetrical two magnons system.