A portable system that will allow electronic messages to be transmitted to and from satellites in absolute secrecy has now been built by researchers at Los Alamos National Laboratory in New Mexico.
The researchers will test the system to send quantum information 10 kilometres through horizontal free space at the start of September. Air density at this at this level approaches that experienced when transmitting information to a satellite 300 kilometres above the Earth.
鈥淭his is a significant step towards that threshold,鈥� says Tim Spiller, of the Quantum Information Processing Group at Hewlett-Packard Laboratories in the UK. 鈥淭his group is leading the world in this area.鈥�
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The furthest that anyone has yet managed to send this type of signal is just two kilometres. But Glen Peterson, who constructed the device at Los Alamos National Laboratory, is confident that the technology will work over 10 kilometres. He says that new photon projection and detection hardware promise to improve the system鈥檚 accuracy dramatically.
鈥淭he next step is to track a satellite and make sure we get the signals right,鈥� he says. 鈥淲e have people developing the hardware to go into satellites.鈥�
Sensitive state
The new system consists of two devices that transmit and receive data encoded as individual photons with a quantum state. The laws of quantum physics mean that any interference with the data stream would disrupt the stream, leading to detection.
Other research institutes have demonstrated quantum cryptography in the laboratory but the technique is not yet used to secure sensitive messages.
In practice, quantum cryptography might only be used to update the 鈥渒eys鈥� used to lock and unlock encrypted messages sent through normal satellite links. This would greatly improve the security of satellite communications but not guarantee total secrecy.
One time keys
However, the system could be used to generate 鈥渙ne time鈥� keys that would provide absolute secrecy for individual satellite communications, although these would require significantly more bandwidth.
Experts say that the technique will probably not be used to perform the majority of communications, such as relaying internet messages, because significant extra cost and effort is required.
鈥淚t鈥檚 going to be used mainly in niche markets such as point-to-point government communications, where you need very high security.鈥� says Nigel Smart, a cryptography expert at the University of Bristol in the UK.