Countries race to achieve space-based quantum communication

MIT Technology Review : Photon-based quantum communication requires individual photons to reach their destination without being absorbed by the transmitting medium, such as Earth’s atmosphere or an optical fiber. As a result, the technique has been limited to distances of just 100 km. To overcome that limitation, researchers have proposed bouncing the photons off orbiting spacecraft and then retransmitting them to Earth. Giuseppe Vallone of the University of Padova in Italy and colleagues recently demonstrated the feasibility of such a technique by using geodetic satellites, which have mirrors called corner-cube retroreflectors to reflect light back to Earth. But the satellites had to have mirrors with metallic coatings to maintain the photons’ polarization, essential to their usefulness in transmitting information. The researchers selected four such satellites; for comparison, they also used a Japanese satellite with uncoated mirrors. When Vallone and colleagues bounced polarized photons off the satellites, they found that the error rate for the four satellites with coated reflectors was less than 11%, which is considered acceptable. Chinese and European scientists have already announced plans for quantum communication experiments, while the US has yet to weigh in.