A modified Hong-Ou-Mandel interferometer for two-parameter sensing

A modification of the standard Hong-Ou-Mandel interferometer is proposed that allows one to recover two independent parameters (delays) via the coincidence counts measured at the output of the setup. In the ideal case where such delays are sufficiently stable with respect to the mean wavelength of the pump source, properly symmetrized input bi-photon states allow one to pinpoint their values through the identification of a zero in the coincidence counts, a feature that cannot be simulated by semiclassical inputs. Besides, in the presence of fluctuating parameters the zero in the coincidences is washed away: still the bi-photon state permits to recover the values of parameters with a visibility which is higher than the one allowed by semiclassical sources. The detrimental role of loss and dispersion is also analyzed and an application in the context of quantum positioning is presented.