Experimental test of the delayed single-photon self-interference effect

A modified version of the delayed single-photon self-interference experiment is performed using a sample of Pr:Y₂SiO₅ for detecting the interference pattern. Instead of using a beam splitter and two spatially separated paths for the light to travel towards the material, acousto-optic modulators are used to create two light pulses and let the pulses travel along the same path towards the material. Attenuated laser pulses are used, with energies down to less than 0.6 photons per pulse pair, and accumulated 7*10⁹ such pulse pairs before reading out the resulting frequency dependent modulation of the population in the material. The signals for different average photon numbers in the pulse pairs are compared to conclude that the observed signal is due to the pulse pairs containing a total of only one photon.