NEC Transmits Quanta

TOKYO -- NEC Corporation, the Telecommunications Advancement Organization of Japan and the Japan Science and Technology Corporation have succeeded in realizing the world's first 100-km-long single-photon transmission, using a quantum cryptography system with low cost optical fibre. This system guarantees secure network communication by the laws of quantum mechanical physics.

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 enables the system. The transmitter is equipped with a filter that can purify the single-photon spectrum.

The main features of this system are as follows:

1. The fibre used in this experiment has the same transmission loss and scattering as is commonly experienced in field transmission. Therefore this transmission can be realized using conventional infrastructure.

2. There is a 50-fold improvement in signal to noise ratio in the receiving system. Long distance transmission, over 200-km, will be possible by adopting low loss and low scattering fibre, as the transmission distance is determined by back-scattered photons from the transmitting fibre, not by the receiver.

This system allows quantum cryptography transmissions in metropolitan optical networks. It is also expected that it will contribute to the realization of an optical fibre network system that requires advanced safety levels against code breaking.

With recent trends toward electronic commerce and elections, society is becoming increasingly reliant on and connected to networks for everyday activities. As a result, security for the private information of businesses and individuals is becoming crucial. Quantum cryptography is attracting considerable interest 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; it is not reliant on calculation capability but on the principles of physics.

As intercity network transmission distance is assumed to be about It is reasonable to assume a distance range of 100km for intercity networks, making transmission along existing optical fibre networks highly desirable.

The collaboration between NEC and TAO is expected to accelerate development of the quantum cryptography system and its introduction to metropolitan networks.

NEC Corp.