How China built a single-photon detector that works in space
One of the emerging uses for single photons is to pack them with quantum information and send them to another location. This technique, known as quantum communication, exploits the laws of physics to make sure the information cannot be read by any eavesdropper.
One challenge is to find ways to send this quantum information around the world. That’s difficult because the information is fragile—any interaction between the photons and their environment destroys it.
So Chinese physicists have come up with a workaround: beam the photons to an orbiting satellite, which relays them to another location on Earth’s surface. In this way, the uncomfortable passage through the atmosphere can be minimized.
But there is a problem. Quantum communication requires detectors that can spot and measure single photons.
Today, Meng Yang and colleagues at the University of Science and Technology of China in Hefei say they have solved the problem. They have even tested their machine over the last two years on an orbiting satellite and say it works well.
So the trick with avalanche breakdown is to set up a voltage that rapidly accelerates a free electron to high enough speeds to knock other conducting electrons free. This creates a chain reaction—an avalanche—that results in a much larger and more easily detectable current.
So the task for Yang and co was to find ways to protect and enhance the performance of commercial off-the-shelf single-photon detectors so that they can operate in space.
These experiments have set the scene for a new generation of space-based quantum communication.
In the meantime, the rest of the quantum physics world has looked on with envy. China has a clear lead in space-based quantum communication, albeit with help from European researchers in key areas.
By contrast, US plans have stalled.