Asymptotic performance of optimal state estimation in quantum two level system

TL;DR

This paper establishes an asymptotic bound on the accuracy of quantum state estimation in two-level systems, demonstrating that quantum correlations in the measurement apparatus can improve estimation precision.

Contribution

It proves the bound can be achieved with quantum correlations and shows measurements without such correlations cannot attain this bound.

Findings

Quantum correlations enhance asymptotic estimation accuracy.

The derived bound is achievable in any quantum two-level system model.

Measurements lacking quantum correlations cannot reach the optimal bound.

Abstract

We derived an asymptotic bound the accuracy of the estimation when we use the quantum correlation in the measuring apparatus. It is also proved that this bound can be achieved in any model in the quantum two-level system. Moreover, we show that this bound of such a model cannot be attained by any quantum measurement with no quantum correlation in the measuring apparatus. That is, in such a model, the quantum correlation can improve the accuracy of the estimation in an asymptotic setting.