Last Monday, Jian-Wei Pan and a team from the University of Science and Technology of China, in Shanghai, revealed the results of an experiment in which they successfully sent single photons on a round trip to an orbiting satellite, then detected those same photons back on Earth.
The scheme proves that a satellite can beam single photons back to our planet even while it’s in orbit, a necessity for quantum communications.
Basically, Jian-Wei and his cohorts pointed a couple of telescopes at a targeted satellite, which was covered with reflectors that could bounce a laser beam back to wherever it came from on Earth. One telescope was set up to shoot pulses of light at the satellite, while the other looked for evidence of the reflection.
Each beam of light started off with 1 billion photons, and the pulse was repeated millions of times a second. On average, for every pulse of light, just one photon made the return trip back home. They reported detecting these homeward-bound photons at a rate of about 600 per second.
“These results are sufﬁcient to set up an unconditionally secure QKD link between satellite and earth, technically,” the team wrote in their paper.