Quantum information is usually sent by light that is 'entangled'. This means that properties of photons sent between the two parties are quantum mechanically linked, and that the information changes when it is 'read', thus providing theoretically perfect data security. But entanglement is delicate and can easily be disrupted by factors such as atmospheric turbulence — so the receiver cannot tell whether a message was intercepted, or if the weather got in the way.
Ulrik Andersen of the Technical University of Denmark and his co-workers think that they can. They sent entangled light pulses through a simulated atmosphere, finding that when the pulse's amplitude fell within a certain range, it remained entangled.
The authors hope that the technology will help to improve the long-distance transfer of quantum information.