The optical-to-electrical conversion, which is the basis of optical detectors, can be linear or nonlinear. When high sensitivities are needed single-photon detectors (SPDs) are used, which operate in a strongly nonlinear mode, their response being independent of the photon number. Nevertheless, photon-number resolving (PNR) detectors are needed, particularly in quantum optics, where n-photon states are routinely produced. In quantum communication, the PNR functionality is key to many protocols for establishing, swapping and measuring entanglement, and can be used to detect photon-number-splitting attacks. A linear detector with single-photon sensitivity can also be used for measuring a temporal waveform at extremely low light levels, e.g. in long-distance optical communications, fluorescence spectroscopy, optical time-domain reflectometry. We demonstrate here a PNR detector based on parallel superconducting nanowires and capable of counting up to 4 photons at telecommunication wavelengths, with ultralow dark count rate and high counting frequency.
@article{arxiv.0712.3080,
title = {Superconducting nanowire photon number resolving detector at telecom wavelength},
author = {Aleksander Divochiy and Francesco Marsili and David Bitauld and Alessandro Gaggero and Roberto Leoni and Francesco Mattioli and Alexander Korneev and Vitaliy Seleznev and Nataliya Kaurova and Olga Minaeva and Gregory Goltsman and Konstantinos G. Lagoudakis and Moushab Benkhaoul and Francis Levy and Andrea Fiore},
journal= {arXiv preprint arXiv:0712.3080},
year = {2009}
}