Single-Photon Source
We are engineering a technique for producing single photons that can be used for various quantum information applications such as quantum cryptography and optical quantum computing. Our source is based on spontaneous parametric downconversion of a 355-nm pulsed pump laser, frequency-tripled from a 1064-nm Nd:YAG laser. The UV pump is cycled though a BBO downconversion crystal that is phase-matched to produce a pair of photons, a signal at 702 nm and an idler at 718 nm. The energy of the pump pulses are low, such that the mean number of photon pairs produced from a pass through the crystal is less than 1. However, since the daughter photons are entangled, when we detect the presence of an idler photon, we know with high probability that a signal photon has been created in the conjugate mode. We cycle the pump through the crystal several times so that even though there is a low probability of producing a pair on each cycle, there is a high probability that at least one pass has produced a pair. Once we detect an idler photon, we switch the signal photon into a variable delay storage cavity. After we finish cycling the pump though the crystal, when we release the stored single photon. This yields a high probability of producing a single photon Fock state at a predetermined time while simultaneously minimizing probability of producing two or more photons.