The researchers described how they have demonstrated the first experimental proof of a quantum decoy technique to encrypt data over fiberoptic cable. In quantum cryptography, laser light particles (photons) carry complex encryption keys through fiberoptic cables, dramatically increasing the security of transmitted data. Conventional encryption is based on the assumed complexity of mathematical problems that traditional computers can solve.
But quantum cryptography is based on fundamental laws of physics - specifically, Heisenberg's Uncertainty Principle, which tells us that merely observing a quantum object alters it.
The technique varies the intensity of photons and introduces photonic "decoys," which were transmitted over a 15-kilometer telecommunication cable. After the signals are sent, a second broadcast tells the receiving computer which photons carried the signal and which were decoys. If a hacker tries to "eavesdrop" on the data stream to figure out the encryption key, the mere act of eavesdropping changes the decoys - a clear sign to the receiving computer that the data has been intercepted.
"Quantum cryptography is trying to make all transmissions secure, so this could be very useful for online banking, for example," said Professor Hoi-Kwong Lo, an expert in physics and electrical and computer engineering at the university's Centre for Quantum Information and Quantum Control and the senior author of a new study about the technique.
"The idea can be implemented now, because we actually did the experiment with a commercial device."