A Spontaneous Parametric Downconverion Source for Tests of Single Photon Quantum Mechanics

During the spontaneous parametric downconversion process, a single photon of one frequency is converted into two photons of lower frequency in a nonlinear crystal. The input wave is referred to as the ``pump'' and the output waves are referred to as the ``signal'' and ``idler''. The process is said to be ``spontaneous'' because there are no input signal or idler fields. Rather, these fields are generated spontaneously inside the nonlinear crystal. The process is ``parametric'' because it depends on the electric fields, rather than just their intensities. This creates a definite phase relationship between the input and output fields. It is called ``downconversion'' because the signal and idler fields are at a lower frequency than the pump field. The setup, operation, and performance of a spontaneous parametric downconversion source will be described, as well as future applications of this source for tests of single photon quantum mechanics.