A method for quantum communication that is free from sensitivity to alignment between parties is demonstrated in Nature Communications this week. The technique lifts some of the more stringent requirements for practical quantum communication, and may be useful for satellite-based experiments.
Quantum communication exploits features of quantum physics like entanglement between particles to enable communication tasks that aren’t possible through normal routes. However, because of the precise nature of the measurements required, the two parties must have a shared reference frame to compare their measurements to. Fabio Sciarrino and colleagues circumvent this restriction by using liquid crystal devices to encode photons – the information carrying quantum bits – from one state into another that is insensitive to the orientation of the detector. Photons are generated with quantum information encoded into their polarisation and the devices map it into their angular momentum instead. The receiving party uses another liquid crystal device to decode this information back into its easily-readable polarisation state, irrespective of relative orientation of both parties. The authors demonstrate the scheme for a number of quantum communication protocols and outline its feasibility for universal alignment-free communication, including long-distance and space-based applications.