Researchers from the Department of Physics and Astronomy and the Institute for Quantum Computing at the University of Waterloo are the first to transmit a quantum key securely from a source on the ground to a receiver on an aircraft.
Their story was featured in Tuesday’s edition of the Globe and Mail.
“The system we tested is entirely based on hardware that would go on a satellite for long-distance communication,” said Thomas Jennewein, an associate professor in the Department of Physics and Astronomy and IQC and an affiliate member of the Perimeter Institute for Theoretical Physics. “We demonstrated that everything works as it should. There is an advantage to using a satellite for quantum communication: on the ground photons are absorbed in optical fibre after about 100 kilometres, whereas the absorption loss doesn’t happen outside the atmosphere.”
Jennewein leads the team of experts in Quantum Key Distribution, whose challenge has been to translate quantum encryption instrumentation from controlled, stationary conditions in the lab to the field, where condensation, fluctuations in temperature, and continuous motion can interrupt the photon signal at any time.
Their latest experiment involved placing the custom-built source, called Alice, on the ground in Smiths Falls, Ontario. Alice randomly prepared photons in four different polarization states — horizontal, vertical, +45 degrees and -45 degrees — and sent them to the custom-built receiver payload aboard an aircraft operated by the National Research Council Canada. The receiver payload, called Bob, detected the photons that weren’t lost in the beam spread, analysed the polarisations and recorded the time. Alice and Bob then compared their data to determine which photons made it and their polarization states to construct a secret key.
The secure distribution of cryptographic keys has the potential to provide absolute security for electronic transactions. If you had an eavesdropper named Eve operating in this experiment, she would need to intercept one of the photons, replicate its exact properties including the polarization state and send it along. Not only would it require an additional satellite in between Alice and Bob, but the laws of quantum mechanics state that once you observe a system, you perturb it, so Eve would be immediately detected.
To learn more about the team’s Quantum Encryption and Science Satellite (QEYSSat) project, visit the QEYSSat proposal website.