Unbreakable messages: quantum key distribution

First proposed in 1984 -- the year not the novel -- quantum key distribution (QKD) has gotten a second look from researchers at the Institute of Physics and German Physical Society. QKD systems have been used commercially since 2007, when Switzerland used one to encode the national election ballot results. Most modern-commercial QKD systems utilize lasers that emit photons at random intervals, and as a result are not secure. “The random nature of emission events sometimes results in the emission of two photons very close to each other,” says Dr Sven Hoefling, one of the project coordinators. “Such multiple photon events can be utilized by an eavesdropper to extract information.” To fix this, researchers went back to the the original, more secure, 1984 concept and created the first ever QKD system with a single-photon source. Though single-photon QKD is currently limited to a 40 cm range, Hoefling noted that, “several projects have been funded to [further] develop this technology."