Making photons talk to each other: Nonlinear optics in the quantum domain
Kevin J. Resch · TSpace (University of Toronto) · 2003
I present experimental and theoretical work on extending nonlinear optical effects to the quantum domain. First, I experimentally demonstrate an incoherent nonlinear effect linked to the amplification stage of photon detection in a single-photon counter. The detector, in the high-efficiency regime, does not follow Glauber's quantum mechanical model for photodetection and, as a result, quantum interference effects are observable in the singles rate of one detector. I then go on to theoretically describe and experimentally demonstrate two coherent nonlinear optical effects at the single-photon level. In both experiments, the usually weak nonlinear optical properties of a common nonlinear crystal are enhanced by over 10 orders of magnitude using interference. The first of these coherent processes uses interference to frequency double all photon pairs from a couple of very weak laser beams (containing, on average, less than one photon per pulse). I show how this nonlinearity might be used for “phase-sum” entanglement swapping and an experimental demonstration of Hardy's paradox. The second coherent effect is the dispersive analogue to the first; instead of frequency doubling all of the photon pairs, all photon pairs experience an additional nonlinear phase shift. It is analogous to an immensely enhanced Kerr nonlinearity. This effect is applied to the problem of Bell-state discrimination and can be used to entangle and disentangle the polarization states of a pair of photons under certain conditions. The final experiment in this thesis is a demonstration of a technique for creating coherent superpositions of zero and one photon based on the detection of a single, “trigger” photon.