Spectral distinguishability in ultrafast parametric down-conversion

Abstract

We report a fourth-order interference experiment in which pairs of photons produced in parametric down-conversion pumped by short optical pulses interfere in a Hong-Ou-Mandel interferometer. The visibility of the interference pattern is reduced for larger pump bandwidths. This effect can be understood in terms of the spectral distinguishability of the photon pairs. The interference can be restored by blocking the distinguishing information with a spectral filter.