Quantum correlations in optical metrology: Heisenberg-limited phase estimation without mode entanglement

TL;DR

This paper demonstrates a quantum metrology protocol achieving Heisenberg-limited phase estimation using non-classical photon statistics, without requiring mode entanglement, and shows it outperforms classical limits even with realistic losses.

Contribution

It introduces a new quantum-enhanced optical interferometry scheme that relies solely on photon statistics, not entanglement, to reach the quantum Cramér-Rao bound.

Findings

Achieves Heisenberg-limited sensitivity with standard linear optics.

Quantum advantage derives from photon statistics, not entanglement.

Significant performance improvement over shot-noise limit with realistic losses.

Abstract

The quantum fisher information and quantum correlation parameters are employed to study the application of non-classical light to the problem of parameter estimation. It is shown that the optimal measurement sensitivity of a quantum state is determined by its inter-mode correlations (which depends of path-entanglement) and intra-mode correlations (which depends of the photon statistics). In light of these results, we consider the performance of quantum-enhanced optical interferometers. Furthermore, we propose a Heisenberg-limited metrology protocol involving standard elements from passive and active linear optics, for which the quantum Cram\'{e}r-Rao bound is saturated with an intensity measurement. Interestingly, the quantum advantage for this scheme is derived solely from the non-classical photon statistics of the probe state and does not depend of entanglement. We study the performance of this scheme in the presence of realistic losses and consequently predict a substantial enhancement over the shot-noise limit with current technological capabilities.