Sending quantum messages over long distances will be challenging. The signal will have to be amplified every few hundred kilometres, but conventional optical amplification would destroy the quantum message.
In a quantum information system, if you measure the light, you will destroy the information encoded on it. You need to store the light itself.
“We have to catch and store the light, but we’re not allowed to look at it to see what information it contains. If the system is working, the light will be exactly the same when we let it out again. We do this by absorbing the light into a cloud of atoms,” says Dr Ben Buchler.