Quantum light in complex media and its applications

Photons are often referred to as flying quantum bits, a phrase that emphasizes both their quantum character and their ability to carry quantum information between two distant points. To what extent this holds for complex disordered media, such as the turbulent atmosphere or multimode optical fibres, is an active avenue of research. Over the past few decades physicists have discovered fascinating transport properties of classical light in complex media and developed incredibly powerful tools for controlling it. Recently, these findings have been extended to the quantum realm, demonstrating that quantum properties of light can also be controlled while traversing a complex scattering medium. In this Perspective we highlight some of the main developments in this endeavour, as well as their relevance to applications in quantum key distribution, quantum authentication and Boson sampling.