title: Phase-reference monitoring in coherent-state discrimination assisted by a photon-number resolving detector.
abstract: Phase estimation represents a crucial challenge in many fields of Physics, ranging from Quantum Metrology to Quantum Information Processing. This task is usually pursued by means of interferometric schemes, in which the choice of the input states and of the detection apparatus is aimed at minimizing the uncertainty in the estimation of the relative phase between the inputs. State discrimination protocols in communication channels with coherent states also require the monitoring of the optical phase. Therefore, the problem of phase estimation is relevant to face the issue of coherent states discrimination. Here we consider a quasi-optimal Kennedy-like receiver, based on the interference of two coherent signals, to be discriminated, with a reference local oscillator. By means of the Bayesian processing of a small amount of data drawn from the outputs of the shot-by-shot discrimination protocol, we demonstrate the achievement of the minimum uncertainty in phase estimation, also in the presence of uniform phase noise. Moreover, we show that the use of photon-number resolving detectors in the receiver improves the phase-estimation strategy, especially with respect to the usually employed on/off detectors. From the experimental point of view, this comparison is realized by employing hybrid photodetectors.
authors.affiliation: Department of Physics, University of Milan, via Celoria 16, I-20133 Milano, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Bina
authors.affiliation: Department of Science and High Technology, University of Insubria and CNISM UdR Como, Via Valleggio 11, 22100 Como, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Allevi
authors.affiliation: Institute for Photonics and Nanotechnologies, CNR, and CNISM UdR Como, Via Valleggio 11, 22100 Como, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Bondani
authors.affiliation: Department of Physics, University of Milan, via Celoria 16, I-20133 Milano, Italy.|INFN Sezione di Milano, I-20133 Milano, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Olivares