Quantum Fisher Information of an Open and Noisy System in the Steady State

TL;DR

This paper investigates the quantum Fisher information of a steady-state two-qubit system under noise and reset mechanisms, revealing conditions for enhanced QFI and its relation to entanglement measures like concurrence and negativity.

Contribution

It provides a detailed analysis of how reset and decoherence parameters influence QFI, entanglement, and optimal measurement directions in an open, noisy quantum system.

Findings

QFI per particle exceeds shot noise limit under specific parameters

Entanglement correlates with QFI being greater than 1

Optimal measurement direction varies with system parameters

Abstract

We study the quantum Fisher information (QFI) per particle of an open (parti- cles can enter and leave the system) and dissipative (far from thermodynamical equilibrium) steady state system of two qubits in a noise which is decoherence. We show the behavior of QFI per particle of the system due to changes of re- set and decoherence parameters r and {\gamma} respectively. The parameter r is the strength of the reset mechanism, {\gamma} is the strength of decoherence and in our case it is dephasing channel. The parameters {\gamma} and r are real numbers. We observe that the reset parameter must be bigger than decoherence parameter. We have found that by choosing coupling parameter g as 5{\gamma} the QFI per particle is 1.00226 which is greater than shot noise limit at {\gamma} = 0.5 and r = 14 . Also the concurrence and negativity of the such state have been calculated and they are found as 0.0992486 and 0.0496243 respectively. We have shown that when the concurrence and negativity of some specific states different than zero, which means the state is entangled, the QFI of the system is greater than 1. The QFI per particle, concurrence and negativity shows that the chosen case is weakly entangled. We discovered that the optimal direction depends on the parameters r and {\gamma} and a change in the direction effects the behavior of the QFI of the system.