Communications made using quantum effects are perfectly secure and can also detect if an attempt is made to eavesdrop. The problem is that maintaining the integrity of the quantum communication is technically very difficult, including the need to detect individual photons of light accurately.
Mitsubishi has developed an accurate single-photon detector operating on standard 1,550-nanometer laser light over an optical fibre, with an error rate of 7.6%. Transmission rate is 7.2 bits per second.
To build a fully secure integrated communication system, the quantum transmission is only used for exchanging the encryption keys, which are typically 128 bits long.
Because of the nature of quantum phenomena, this transaction can be made unbreakable. Once the sender and receiver have exchanged encryption keys in this way, the full message is sent using standard high-speed communication methods, with the messages encrypted by the exchanged keys.
Mitsubishi intends to commercialise this quantum cryptosystem for users needing very high security, such as those in government, defence and banking.