Air-to-ground quantum communication

Abstract

Quantum key distribution 1,2 (QKD) is the first commercial application in the new field of quantum information with first routine applications in governmental and financial sectors 3 and with successful demonstrations of trusted node networks 4,5. Today, the grand goal is efficient long range key distribution either via quantum repeaters 6 or via satellites 7-9 in order to enable global secure communication. On the way to QKD via satellites a free-space demonstration of secure key distribution was performed over 144 km between two ground stations 10. This scenario is comparable to links between satellites in low earth orbits (LEO) and ground stations with respect to both attenuation and fluctuations. However, we still miss key exchange with rapidly moving platforms. Here we prove for the first time the feasibility of BB84 quantum key distribution between an airplane and a ground station. Establishing a stable and low noise quantum communication channel with the plane moving with 290 km/h at a distance of 20 km, i.e., 4 mrad/s, our results are representative for typical communication links to satellites 11 or to high altitude platforms. Quantum key distribution provides a whole new level of information security. Any information gained by eavesdropping on the quantum channel can be quantified by the observed transmission noise, the quantum bit error ratio (QBER) 12. Security proofs, solely based on the laws of quantum mechanics, show how to determine the necessary amount of privacy amplification (i.e., key shrinkage according to the QBER) to eliminate the knowledge of a possible adversary 13. Starting with a first quantum channel of 30 cm length in 1989 14 quantum key distribution quickly was enabled on successively longer distances. Two main branches for communicating qubits encoded with quantum states of light were established: either via telecom fiber channels or via free-space transmission. In both cases increasing attenuation and noise limit the maximum distance for a successful key distribution to typically 150−200 km 10,15,16. So far, long range free-space quantum communication experiments used a direct line of sight either between two Canary Islands (144 km) or across a lake in China (95 km) to demonstrate free-space QKD, entanglement distribution 10,17-19 , or quantum teleportation 20,21. In spite of this remarkable progress, all quantum communication so far was performed with stationary systems only. Contrary, for classical optical free-space communication high bandwidth links to aircrafts and satellites have been shown to be feasible in recent years 11,22,23. Here we report on an experiment combining recent advances in classical and in quantum optical technologies to demonstrate the feasibility of quantum key distribution from an airplane to ground (fig. 1). Major challenges in this experiment are the higher pointing requirements compared to classical free-space communication, the development of a precise compensation technique to account for the relative rotations of airborne and ground station qubit en...

Free-space quantum key distribution to a moving receiver

“…Recent demonstrations of QKD using moving transmitters [22,23] imitate the case of a transmitting satellite platform, albeit without a traveling platform reaching the angular speed of a low-Earth-orbit (LEO) satellite. In contrast, a satellite-based quantum receiver is somewhat less complex to develop, and adds flexibility to utilize multiple different source technologies, including attenuated laser pulses and entangled photons [24].…”

Entanglement-based quantum key distribution with biased basis choice via free space

“…Along this line, the free-space quantum communication systems have been successfully demonstrated over large scale distances [11][12][13], with more practical and compact systems [14]. Recently, a series of experimental demonstrations are presented for feasibility tests of ground-satellite quantum key distribution [15,16] and teleportation [17,18].…”

Air to ground quantum key distribution

“…This work [40,41], thus, was enabled by a collaboration with the German Aerospace Center (DLR) in Oberpfaffenhofen, Germany. The free-space experimental laser terminal 2 (FELT2, fig.…”

“…While there was an online synchronization and sifting done, this was primarily intended to provide fast feedback about the QKD performance and estimates for the transmission parameters. Here, a more detailed and adapted analysis will be described allowing for optimization of the filtering in order to maximize the final key rate [40].…”

“…In this work [40,41], both these worlds -long distance quantum communication and free-space optical data links to moving platforms -shall be combined in a first experiment proving the feasibility of QKD from an airplane to an optical ground station. The demonstration is enabled by the recent advances in both fields and intends to constitute a major milestone on the way to QKD applications in space.…”