Quantum crypto secrets from Japan

Data sent along 200m of optical fibre at 1 kbps

Mitsubishi and Hokkaido University have completed a latest round of experiments in quantum cryptography over optical fibres. The two organisations say that their quantum cryptographic system is a success, and could have important implications for optical fibre networks already in use.

The data was sent along 200 meters of optical fibre at a rate of one kbps. Not exactly fast, but there we go. The researchers reported a quantum bit rate error of one percent, which was kept low by the ability of the system to compensate for fluctuations in the phase and polarisation of the light.

Quantum cryptography was first demonstrated in the US in 1989. It exploits the bizarreness of the quantum world, specifically the way a quantum system responds to observation.

Two parties wish to share a key that they can used to encrypt messages sent between them. To establish this key, the first party encodes information in the quantum states of individual optical photons and transmits them to the second party.

The receiver sorts the incoming photons according to their states and sends them to sensitive photo-detectors.

Because of the quantum nature of light, any potential eavesdroppers disrupt the system, changing the nature of the transmission so that it becomes meaningless, simultaneously alerting both parties to the eavesdroppers' presence.

Early experiments in the field involved transmission of a message across a short distance in a vacuum. This is one of few successful experiments using optical fibre as the transmission medium, and researchers are claiming that it is the first such experiment to be conducted in Japan.

Quantum cryptography is an important area of research because its security is not dependent of massively complex algorithms that could be foiled by a sufficiently powerful computer or a sustained attack. Because it is based on fundamental physical properties of the world, it is essentially uncrackable.

Sounds fairly groovy to us. ®

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