Single - Photon Detection of 1 . 55 gm Entangled Light and Frequency Upconversion in Periodically Poled Lithium Niobate for

Entanglement generation, single-photon detection, and frequency upconversion are all key ingredients of a proposed quantum communication scheme. We have demonstrated single-photon detection at 1.55 jim with commercial indium gallium arsenide avalanche photodiodes that were passively quenched, thermoelectrically cooled, and gated to operate above breakdown voltage in Geiger mode. When cooled to -50'C we obtained reliable photon-counting operation with quantum efficiencies of up to 20% at 1.55 gm, dark count probabilities of 0.12% per 20 ns gate, and negligible afterpulses at repetition rates of up to 200 kHz. The indium gallium arsenide single-photon detector was utilized to demonstrate time entanglement of twin photons from a frequency-nondegenerate quasi-phase-matched optical parametric downconverter with collinear and co-polarized outputs at 808 nm and 1.56 gm. We have designed and fabricated a 6-mm-long periodically poled lithium niobate crystal with an 11.6 [tm grating period for first-order type-I quasi-phase-matched sum frequency generation. Upconversion of 1.609 gm light with a strong pump at 1.064 pm resulted in a sum-frequency signal at 640 nm near the peak silicon detection window. We achieved single-pass conversion efficiency of up to 0.65% with 332 mW of pump power in good agreement with theoretical predictions. Thesis Supervisor: Franco N. C. Wong Title: Principal Research Scientist, Research Laboratory of Electronics