Ancilla-assisted frequency estimation under phase covariant noises with Greenberger-Horne-Zeilinger states

TL;DR

This paper investigates how ancilla-assisted strategies can enhance frequency estimation sensitivity under phase covariant noises, providing theoretical bounds and demonstrating robustness against specific noise types.

Contribution

It extends previous work by deriving ultimate frequency sensitivity bounds with ancilla assistance under Markovian covariant phase noises and identifying optimal measurement strategies.

Findings

Quantum Fisher information bounds for frequency sensitivity under phase covariant noise.

Ancilla-assisted strategies can preserve sensitivity in specific noisy environments.

Optimal measurements can saturate the theoretical sensitivity bounds.

Abstract

It has been demonstrated that the optimal sensitivity achievable with Greenberger-Horne-Zeilinger states is the same as that with uncorrelated probes in the frequency estimation in the presence of uncorrelated Markovian dephasing [S. F. Huelga, et al., Phys. Rev. Lett. 79, 3865 (1997)]. Here, we extend this issue by examining the optimal frequency sensitivities achievable by the use of ancilla-assisted strategy, which has been proposed recently for robust phase estimation. We present the ultimate frequency sensitivities bounded by the quantum Fisher information for a general case in the presence of Markovian covariant phase noises, and the optimal measurement observables that can saturate the theoretical sensitivity bounds. We also demonstrate the effectiveness of the ancilla-assisted strategy for preserving frequency sensitivities suffering from specific physically ground noises.