World\’s Longest Single-Photon Transmission Record Extended to 150Km

NEC Corporation, Telecommunications Advancement Organization of Japan (President: Futoshi Shirai, “TAO”), and Japan Science and Technology Agency President: Kazuki Okimura, “JST”) have jointly succeeded in realizing the world’s longest 150-km-long single-photon transmission, far surpassing their previous record of a 100-km-long transmission announced in July, 2003.
Achieved through a newly developed quantum cyrptography system consisting of optical planar circuits based on Planar Lightwave Circuit (PLC) technology, this transmission enables secure network communication supported by the principles of quantum mechanical physics. Due to wide-area coverage (up to 150 km), this system can realize quantum cryptography transmissions in optical networks in metropolitan areas, and is expected to contribute to the realization of an optical fiber network system requiring advanced safety levels to prevent against code-breaking in the future.

This system is enabled by an optical planar circuit (developed by NEC under the TAO project ‘Research and Development on Quantum Cryptographic Technology’) and a low-noise photon receiver (jointly developed last year by NEC and the Imai Quantum Computation Information Project* (ERATO, JST).) The main features of this system are as follows:

1. Stable one-way photon transmission which reduces the noise of backscattered photons from the optical fiber to below one-tenth that of the conventional round-trip systems.

2. Suppression of the deterioration in photon-detection sensitivity that occurs due to the widening of the photon-pulse width that accompanies long fiber transmissions.

3. Tenfold increase in signal-to-noise ratio as compared with current systems (due to the realization of the above two features.)

Present cryptography systems do not guarantee unconditional safety as their security is based on the limitated calculation abilities of present computers, however, quantum cryptography provides unconditionally secure network communication and safety, even when these capabilites are infinite. This is because quantum cryptography is not reliant on calculation capability but on the principle of physics. Therefore, its development is now attracting considerable attention on a global scale.

“As a result of recent trends toward electronic commerce, society is becoming increasingly reliant on and connected to networks, thus information security of individuals and companies is becoming an increasingly important issue,” said Kazuo Nakamura, senior manager at NEC’s Fundamental and Environmental Research Laboratories. “NEC’s quantum cryptography research is acelerating with each new achievement putting us ahead of the competition, thus allowing us to contribute to overall development in this field.”

* ERATO: Exploratory Research for Advanced Technology (Project Director: Hiroshi Imai, Department of Computer Science, Graduate School of Information Science and Technology, The University of Tokyo).

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