Experiments with Downconverted Photons: The Quantum Eraser and Interference of Single Photons Using Pancharatnam’s Phase

Matthew Pysher

Advisor: Dr. Enrique Galvez

These experiments investigate properties of light at the single photon level. We generate pairs of 915.8-nm photons through parametric downconversion by sending a beam of 457.9-nm light through a BBO crystal. These downconverted photons are detected using two avalanche photodiodes. In one portion of this project, we create a distinguishable characteristic in one arm of a Mach-Zender interferometer by adding a half waveplate. This will destroy the single photon interference pattern that is observed when single photons are sent through an interferometer with indistinguishable arms. We will regain the interference pattern by adding a 45ْ polarizer in front of our avalanche photodiode. This polarizer effectively erases the distinguishing information added by the half waveplate. In the other part of this project, we display the interference of single photons by using a series of waveplates to introduce a geometric phase onto one arm of a Mach-Zender interferometer. An interference pattern can be observed in the coincidence count rates as a function of this geometric phase.