Enabling Technologies for High-Rate, Free-Space Quantum Communication

Davide Orsucci, Jorge Rosano Nonay, Amita Shrestha +1 more

Free-Space Optical (FSO) communication is a technology that enables ultra-high-rate data exchange and will be crucial in enabling secure Quantum Key Distribution (QKD) over long distances. However, FSO communication systems are comparatively complex technologies, comprising a variety of subsystems that all have to work together in a coordinated way. Hence, assessing the feasibility of establishing a (classical or quantum) link in a given communication scenario is a difficult task in itself. Here we introduce QCalc, a software tool that aims at easing and streamlining this process, allowing the user to keep track of all the relevant parameters in a link budget. This software computes the total transmissivity, and thus, the signal intensity observed at the receiver for any given parameters of the transceivers and the FSO communication channel. The estimated signal intensity can then be used to compute either the link budget in a classical communication scenario or the secure key rate of a QKD protocol.

Victor V. Kozlov, Matthias Freyberger

Samuele Altilia

Pierre Didier, Hamza Dely, Olivier Spitz +5 more

A combination of unipolar quantum laser, modulator and detector allows us to demonstrate a free-space communication at 40 Gbits/s and 9 µm far-infrared wavelength. The distance between the emitter and the receiver is 31 meters.

Nicoló Lo Piparo

Florian Moll, Harald Weinfurter, Markus Rau +5 more

A worldwide growing interest in fast and secure data communications pushes technology development along two lines. While fast communications can be realized using laser communications in fiber and free-space, inherently secure communications can be achieved using quantum key distribution (QKD). By combining both technologies in a single device, many synergies can be exploited, therefore reducing size, weight and power of future systems. In recent experiments we demonstrated quantum communications over large distances as well as between an aircraft and a ground station which proved the feasibility of QKD between moving partners. Satellites thus may be used as trusted nodes in combination with QKD receiver stations on ground, thereby enabling fast and secure communications on a global scale. We discuss the previous experiment with emphasis on necessary developments to be done and corresponding ongoing research work of German Aerospace Center (DLR) and Ludwig Maximilians University Munich (LMU). DLR is performing research on satellite and ground terminals for the high-rate laser communication component, which are enabling technologies for the QKD link. We describe the concept and hardware of three generations of OSIRIS (Optical High Speed Infrared Link System) laser communication terminals for low Earth orbiting satellites. The first type applies laser beam pointing solely based on classical satellite control, the second uses an optical feedback to the satellite bus and the third, currently being in design phase, comprises of a special coarse pointing assembly to control beam direction independent of satellite orientation. Ongoing work also targets optical terminals for CubeSats. A further increase of beam pointing accuracy can be achieved with a fine pointing assembly. Two ground stations will be available for future testing, an advanced stationary ground station and a transportable ground station. In parallel the LMU QKD source size will be reduced by more than an order of magnitude thereby simplifying its integration into future free-space optical communication links with CubeSats.