Single Photon Interference by Attenuation

This project represents the initial phase of developing a Bell’s Inequality Test of Quantum Mechanics laboratory at Central Washington University. We set up and performed an investigation of the interference of light using a double slit apparatus. For the experiment, a 632.8 HeNe laser beam was passed through an optical system consisting of mirrors, neutral density filters, linear polarizers, irises, multiple lenses and a pinhole. The light was spatially filtered, producing a clean profile, and collimated by the placement of the irises, lenses, and pinhole within the path of the light. The beam intensity was varied using the neutral density filters and polarizers to obtain interference patterns consistent with single photon events. A SBIG ST-7 CCD camera was used as detector and the interference fringes measured using pixel specifications of the CCD chip. The camera was evaluated for effectiveness as a single photon detector by attenuating the beam until its irradiance was consistent with single photon events in the camera pixels for one exposure and examining the signal. These attenuation procedures were then employed using single photon counting modules to detect the interference pattern. The single photon counting modules provided a TTL signal corresponding with single photon detection. A statistical analysis of two detector’s counts is consistent with detection of the phenomenon of single photon interference.