Quantum multiphase estimation in an integrated photonic circuit

Quantum Metrology is one of the most important quantum technologies where quantum resources are exploited to enhance the estimation of unknown parameters. In this context, since realistic scenarios generally involve more than one parameter, quantum multiparameter estimation is a central and very active research area. Several open questions are still unclosed and experimental platforms able to perform multiparameter estimation protocols have to be developed.
We realized a reconfigurable photonic integrated circuit, built through the femtosecond lase writing technique, able to perform simultaneous multiphase estimation with photonic quantum states. The circuit realizes a three arm interferometer and is characterized by high tunability that allows to change the two independent phase shifts. Firstly, we demonstrate quantum enhanced two-phases estimation by using two-photon probes. Then we provide a demonstration of a Bayesian adaptive protocol able to saturate, in the limited data regime, the sensitivity bound on the estimation of the two phases when single photon probes are employed.