Mitsuru Matsui

Analysis of Single-Photon-Detection Characteristics of GaInAs/InP Avalanche Photodiodes

An effective method to analyze the origin of primary dark counts is presented for single-photon-detection avalanche photodiodes (APDs) operated in the gated Geiger modes. It is revealed that a band-to-band tunneling model reproduces the experimental data very well for GaInAs/InP single-photon-detection APDs, while a phonon-assisted tunneling model fails. Therefore, we concluded that primary dark counts are dominated by the band-to-band tunneling for the GaInAs/InP single-photon-detection APDs. Then, we calculate the dark count probability and the detection efficiency by modeling the band-to-band tunneling. It is found that the ratio of the dark count probability to the detection efficiency is reduced by decreasing the impurity concentration of the multiplication region and of the p-type window.

Field experiments of quantum cryptosystem in 96 km installed fibers

We have successfully demonstrated quantum cryptosystem in 96 km installed fibers between Osaka and Kyoto, Japan with our dedicated QKD hardware suitable for field experiments. We confirmed that key rate is 8.2 bps and QBER is 9.9%.

Experimental realization of quantum cryptosystem over 87 km

We have successfully implemented telecom-wavelength quantum cryptosystem over 87.5 km (worlds longest) including error correction and privacy amplification. We confirmed that key distribution was performed at a rate of 7.2 bps with a 7.6% QBER.

Heralded single photon source for quantum cryptography at 1550 nm

The paper proposes on the use of non degenerate parametric downconversion PDC in BBO crystal to realize a heralded single photon source. Downconverted photons wavelength can be chosen using phase matching condition.