Air-to-ground quantum communication

Quantum key distribution (QKD) is the first commercial application in the new field of quantum information, with first routine applications in government and financial sectors and with successful demonstrations of trusted node networks. Today, the main goal is efficient long-range key distribution via either quantum repeaters or satellites, with a view to enabling global secure communication. En route to achieving QKD via satellites, a free-space demonstration of secure key distribution was performed between two ground stations, over a distance of 144 km. This scenario is comparable to links between satellites in low Earth orbit and ground stations with respect to both attenuation and fluctuations. However, key exchange with rapidly moving platforms remained to be demonstrated. Here, we prove, for the first time, the feasibility of BB84 QKD between an aeroplane and a ground station. By establishing a stable and low-noise quantum communication channel with the aeroplane moving at 290 km h−1 at a distance of 20 km—that is, 4 mrad s−1—our results are representative of typical communication links to satellites or to high-altitude platforms

Single-photon detectors for optical quantum information applications

The past decade has seen a dramatic increase in interest in new single-photon detector technologies. A major cause of this trend has undoubtedly been the push towards optical quantum information applications such as quantum key distribution. These new applications place extreme demands on detector performance that go beyond the capabilities of established single-photon detectors. There has been considerable effort to improve conventional photon-counting detectors and to transform new device concepts into workable technologies for optical quantum information applications. This Review aims to highlight the significant recent progress made in improving single-photon detector technologies, and the impact that these developments will have on quantum optics and quantum information science