Experimental demonstration of phase estimation advantage in presence of depolarizing noise by using coherent measurements

TL;DR

This paper experimentally demonstrates that global measurements, involving entangling operations, can outperform local measurements in quantum metrology under depolarizing noise, especially when noise characterization is uncertain.

Contribution

It provides the first experimental evidence that global measurements enhance phase estimation accuracy in noisy quantum states compared to local strategies.

Findings

Global measurements outperform local ones in noisy quantum metrology.

Coherent operations enable unambiguous parameter estimation despite noise.

Quantum coherence in measurement devices boosts metrological advantage.

Abstract

We report an experimental investigation of the role of measurement in quantum metrology when the states of the probes are mixed. In particular, we investigated optimized local measurements and general global projective measurements, involving entangling operations, on noisy Werner states of polarization entangled photons. We demonstrate experimentally that global measurement presents an advantage in parameter estimation with respect to the optimized local strategy. Moreover, the global strategy provides unambiguous information about the parameter of interest even when the amount of noise is not well characterized. This shows that the coherence in quantum operations, such as the Bell-state projection device used in our protocol, can be used to further boost the quantum advantage in metrology and play a fundamental role in the design of future quantum measurement devices.