Measure of the tunnelling time of a single photon through a Fabry-Perot cavity

The displacement of the peak of a wavepacket that crosses an empty Fabry-Perot cavity is measured by using photon pairs generated by parametric down conversion, a Hong-Ou-Mandel (HOM) interferometer and coincidence detection. The Fabry-Perot cavity distorts the photon wavepacket. The HOM interferometer is a good tool to map this distortion. We discuss the corrections which must be made in the two-photon inteference results, in order to achieve the true data researched. Even in the absence of active absorbers media or media with inverted atomic populations, superluminal-like effects connected with the tunnelling phenomena are observed. An interpretation of the experimental results in the causality frame is given.