Any objects in the optical path-as big as a wall or as small as a molecule-will reflect some photons and scatter others, depending on the reflectivity of the surface. Normally, if you try to send and receive photons through the air (free-space) for quantum communication, or any other quantum-encoded protocol, you need a direct line-of-sight between transmitter and receiver. 'The ability to transfer quantum coherence via scattered photons means that now you can do many things that previously required direct line-of-sight free-space channels,' said Shihan Sajeed, lead author on the paper and a postdoctoral fellow at the Institute for Quantum Computing (IQC) and in the Department of Physics and Astronomy at the University of Waterloo in Ontario, Canada. This enables new research opportunities and applications in fields ranging from quantum communication to imaging and beyond. In a new paper published in Light: Science & Applications, researchers from the University of Waterloo have successfully demonstrated the transfer and recovery of quantum coherence using photons scattered in free-space for the first time.

Global phase coherence