Scientists have developed a light-emitting diode so precise it sends out a single photon of light when turned on. Such a device could lead to unbreakable quantum cryptography and would make optical networks immune to eavesdropping, they say.

Researchers for Toshiba Europe, working in concert with scientists from Cambridge University, produced the LED with standard semiconductor manufacturing techniques and say it could soon be produced quite cheaply for commercial use. Previous devices that produce a single photon have required expensive lasers or low temperatures, making them unviable for general use.

An LED that produces just a single photon would be incredibly useful for computer security, thanks to the properties of light at the quantum level. Individual photons can be polarized to carry information, and since Heisenberg's Uncertainty Principle tells us that you can't observe a particle without changing it, it would be obvious if someone intercepted the photon. That would let people share cryptographic keys and other messages, while being sure no one has eavesdropped.

Pete Lindstrom, director of security strategies for the Hurwitz Group, says the technology will help cryptographers stay a step ahead of advances in computing power that threaten to crack their codes. Current computers aren't powerful enough to manage the brute-force attacks that try every possible key combination to crack encryption. But advances such as quantum computing will significantly shorten the amount of time in which such breaches can be accomplished. By using quantum cryptography, people can be sure their codes haven't been intercepted and won't be cracked. Says Lindstrom, "Years from now, if quantum computing makes public key cryptography obsolete, it's nice to know quantum cryptography will be there to take over and solve the key distribution problem."