Data sent at four million bits per second over 1km line

Scientists at the US National Institute of Standards and Technology (NIST) have smashed their own record for transferring data encrypted using quantum cryptography.

The team, led by NIST physicist Xiao Tang, managed to send the encrypted data at four million bits per second over a one-kilometre fibre, double the previous record.

Tang also managed to send the data over a four-kilometre line but nowhere near as fast.

The system uses quantum key distribution (QKD) to encode data using individual photons of light in two different quantum states to represent one and zero.

The system is secure because if a third party attempts to view the data they are instantly detected.

"This is all part of our effort to build a prototype high-speed quantum network in our lab," explained Tang.

"When it is completed, we will be able to view QKD-secured video signals sent by two cameras at different locations. Such a system becomes a QKD-secured surveillance network."

The record speed was achieved with an error rate of only 3.6 per cent, which the team considered very low.

The next step will be to process the raw key, using NIST-developed methods for correcting errors and increasing privacy to generate "secret" keys at about half the original speed, or about two million bits per second.

The work is supported in part by the US Defence Advanced Research Project Agency.