NTT Basic Research Laboratories

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Multidisciplinary Materials Design and Science Laboratory
Advanced Applied Physical Science Laboratory
Quantum Science and Technology Laboratory
Nanophotonics Center
Research Center for Theoretical Quantum Physics
May 31, 2007

Quantum key distribution over 200 km long optical fiber

Realization of world’s fastest 10 GHz clock ultra-high speed quantum cryptography system

  NTT Basic Research Laboratories through collaborative research with the Stanford branch of the National Institute of Informatics (NII) and the National Institute of Standards and Technology (NIST) have developed a quantum cryptography system with world’s fastest 10 GHz clock and have succeeded in realizing a quantum key distribution using single photon level light over a long (200 km) optical fiber in a laboratory. This achievement was realized by combining the high clock ready differential phase shift-quantum key distribution technology developed by NTT Basic Research Laboratories and the Stanford branch of NII with an ultra-sensitive and high-temporal resolution superconductive single photon detector developed by NIST.

  This is expected to constitute important basic technology for realizing an ultimately secure long-distance communication network that excludes eavesdropping.

This achievement will be published in the English science journal “Nature Photonics” on July, 1.

=> Quantum Optical State Control Research Group

Fig. 1 Quantum cryptography system with 10GHz clock
(SSPD: Superconductive Sigle Photon Detector)

 Fig. 2 Transmission loss (fiber length) vs Secure key generation rate