Researchers at the U.S. National Institute of Standards and Technology (NIST) have demonstrated a technique that could make quantum cryptography significantly cheaper to implement, moving it nearer to possible commercial acceptance.

The technique, outlined in a paper to be published this month in the journal IEEE Communications Letters, is aimed at cutting the cost of equipment needed for quantum key distribution (QKD), designed to distribute cryptographic keys using a secure system based on the principles of quantum mechanics.

Such systems are typically based on the distribution of photons through a fiber-optic network, with information encoded in the polarization of the photons.

They are designed to allow an absolute level of security, with any attempt to monitor the system by a third party, for instance, necessarily disrupting the system.

However, such systems are expensive to implement, with the most common polarization-based protocol, known as BB84, requiring four single-photon detectors, costing US$5,000 to $20,000 each, the NIST said.

The new method, called detector-time-bin-shift (DTBS), shifts photons into two distinct "time bins."

This means a set of two detectors can be used to sequentially record the two sets of photons, rather than requiring four detectors to simultaneously record all the photons, the NIST said.

In their work on a protocol called B92, the researchers reduced the required number of detectors from two to one, the NIST said.

Further work carried out since the completion of this month's paper further reduced the number of photon detectors needed for the BB84 protocol from four to one, the NIST said.

The arrangement detailed in the paper cuts transmission rates by half, but the NIST system still works at broadband speeds, it said. The organization said its experimental network can encrypt and decrypt webcam-quality video streams in real time using DTBS.

In 2006 the NIST managed to shift quantum-encrypted information at a "raw" throughput of 4 million bits per second across a 1 km-long fiber link.

This was at least twice NIST's previous record, which has been rising since the agency announced it had broken the 1 million bits per second barrier in May 2004. At such transfer rates, it becomes practical to use QKD cryptography to secure a video stream.

In 2005 Toshiba Europe reached the demonstration phase of what it claimed was the first system to use quantum cryptography to secure a real-time video and voice data stream, developed by a 30-person team of scientists working at the company's Cambridge Research Laboratory.