Japanese Nippon Telegraph and Telephone Corp. (NTT) has successfully demonstrated the quantum cryptography with a single photon can be realised in the photonic network of optical fibres. The quantum cryptography is expected to be the last resort of the cryptography protocol, and to enhance enormously the safety of transmitting information.
The result was enabled by combining the original protocol of the quantum cryptography developed by the collaboration of NTT and Stanford University (USA) and the NTT developed optical switch to control the flow of photons.
2005 is the World Year of Physics, and this experiment utilises the quantum effect, which had puzzled Prof. Einstein about a century ago: a single photon is like a particle (quanta) but sometimes behaves like a wave and interferes with itself. Although the modern physics still cannot explain why such an interference occurs, the present work clearly demonstrated that this quantum effect is applicable in the technology of cryptography for the first time.
Quantum cryptography is seen as the next generation cryptographic system to replace the public-key protocol for protecting data. It utilises the property that the quantum state is very delicate to the external environment, and is destroyed when an eavesdropper observes it. Since the secret key encoded in the quantum state, single photon, cannot be identically replicated, the receiver can easily detect if the secret key had been stolen.
With the increasing usage of general networks, such as the Internet, to transmit secret or financial data, the NTT demonstration is seen as an important breakthrough in enhancing security via cryptography.