Seigo Takahashi | Searcharxiv

arXiv2008

Ultra fast quantum key distribution over a 97 km installed telecom fiber with wavelength-division multiplexing clock synchronization

We demonstrated ultra fast BB84 quantum key distribution (QKD) transmission at 625 MHz clock rate through a 97 km field-installed fiber using practical clock synchronization based on wavelength-division multiplexing (WDM). We succeeded in over-one-hour stable key generation at a high sifted key rate of 2.4 kbps and a low quantum bit error rate (QBER) of 2.9%. The asymptotic secure key rate was estimated to be 0.78-0.82 kbps from the transmission data with the decoy method of average photon numbers 0, 0.15, and 0.4 photons/pulse.

quant-ph↗

arXiv2007

High-efficiency single photon detector combined with an ultra-small APD module and a self-training discriminator for high-speed quantum cryptosystems

A single-photon avalanche detector (SPAD) for high-speed quantum-key generation has successfully been developed. It has the highest photon detection repetition frequency and the lowest dark count rate in the world, as a board-mountable sub-system. The SPAD consists of an ultra-small dual-avalanche photodiode (APD) module and a novel discriminator. The APD module design is consistent with cooling capability and high-frequency characteristics. The new module has a 3 GHz bandwidth enabling 1 GHz gate-pulse repetition. The bandwidth is extended 15-fold relative to the most wideband peltier cooled APD module. The discriminator has a self-training mechanism to compensate charge pulse. Dark count rare of the SPAD is reduced 1/10th relative to the lowest dark count single photon detector. The SPAD allows 3.2-fold multiplying the quantum key generation rate in theoretical estimation.

quant-ph↗