7 July 2003 Tokyo Lightwave-- NEC Corp., Telecommunications Advancement Organization of Japan (TAO) and Japan Science and Technology Corp. (JST) have succeeded in realizing the world's first 100-km single-photon transmission using a quantum cryptography system with low cost optical fiber. Under this system, secure network communication is guaranteed by the laws of quantum mechanical physics principles.
This system is enabled by a low-noise photon receiver developed jointly by NEC and the Imai Quantum Computation Information Project* (ERATO, JST) last year, and a high performance transmitter developed by NEC and TAO that is equipped with a filter that can purify the single-photon spectrum. The main features of this system are as follows:
• The fiber used in this experiment has the same transmission loss and scattering as is commonly used in field transmission. Therefore this transmission can be realized using conventional infrastructure.
• There is a 50 time improvement in signal to noise ratio in the receiving system. As transmission distance is not determined by the receiver, but by back-scattered photons from the transmitting fiber, long distance transmission over 200-km will be possible by adopting low loss and low scattering fiber.
This system enables quantum cryptography transmissions in metropolitan optical networks. It is also expected that it will contribute to the realization of an optical fiber network system that requires advanced safety levels against code breaking.
With recent trends toward electronic commerce and electric election, society is becoming increasingly reliant on and connected to networks. As a result information security of individuals and companies is becoming vital. Quantum cryptography is attracting considerable attention because it has the potential to provide unconditionally secure network communication. The present crypto system used worldwide does not guarantee unconditional safety as the calculation abilities of present computers are limited. This is where Quantum cryptography's strength lies in that it provides unconditional safety even if these capabilites are infinite due to the fact that it is not reliant on calculation capability but on the principle of physics. As intercity network transmission distance is assumed to be about 100 km, this transmission length using practical optical fiber has been desired for quantum cryptography.
The collaboration between NEC and TAO is expected to accelerate development of the quantum cryptography system and of its application to metropolitan networks.
* Exploratory Research for Advanced Technology (ERATO, Project Director: Hiroshi Imai, Department of Computer Science, Graduate School of Information Science and Technology, The University of Tokyo)