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

We report an experimental investigation of the role of measurement in quantum metrology when the states of the probes are mixed. In particular, we investigate optimized local measurements and general global projective measurements, involving entangling operations, of 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.

Automated summary

The experimental investigation reveals that global measurements have advantages in quantum metrology compared to optimized local strategies. Even in cases where the amount of noise is not well characterized, the global strategy can provide unambiguous information about the parameter of interest. The coherence in quantum operations, such as the Bell-state projection device used in the protocol, plays a fundamental role in boosting the quantum advantage in metrology and designing future quantum measurement devices.