Physicists at Toshiba have used quantum cryptography to transmit voice and video data over a secure optical-fibre link. The demonstration is significant because it shows that the single-photon encryption technology is compatible with real Internet Protocol (IP) traffic and is also robust enough for deployment on commercial optical-fibre networks. The system was shown to financial institutions at the Department of Trade and Industry in London by Andrew Shields and colleagues from Toshiba Research Europe at the end of April.