A quantum measurement can be described by a set of matrices, one for each possible outcome, which represents the probability operator-valued measure (POVM) of the sensor. Ecient protocols of POVM extraction for arbitrary sensors are required. We present the rst experimental POVM reconstruction that takes explicit advantage of a quantum resource, i.e. nonclassical correlations with an ancillary state. POVM of a photon-number-resolving detector is reconstructed by using strong quantum correlations of twin-beams generated by parametric downconversion. Our reconstruction method is more statistically robust than POVM reconstruction methods that use classical input states.

 

"Ancilla-assisted calibration of a measuring apparatus"
G. Brida, L. Ciavarella, I. P. Degiovanni, M. Genovese, A. Migdall, M. G. Mingolla, M.Paris, F. Piacentini, and S.Polyakov
Phys. Rev. Lett. 108, 253601 (2012)