Wide-angle receiver for long-distance free-space quantum key distribution

Description

Creating a global quantum network has many challenges and may rely on both free-space and in-fibre solutions for its creation. Inherent losses in fibre-optic cables, and limitations with current quantum repeater/amplifier technology mean we cannot rely on fibre-optic for long-haul applications. However short transmission networks are still feasible, and have been demonstrated. Implementing free-space channels which utilise high-altitude platforms or satellite trusted nodes in orbit is seen as the fastest route to achieving long-haul capabilities. Research initiatives around the globe are already performing proof-of-principle studies and field testing components for satellite-based quantum communications.
As coherent light propagates through the turbulent atmosphere, effects such as wavefront distortion and intensity fluctuation can lead to errors in pointing-and-tracking during the quantum key sharing. The resultant errors can greatly increase the quantum-bit error rate for time-bin quantum key distribution protocols. This is due to the reduction in interferometric visibility with the changing angle-of-incidence as the beam walks. For time-bin quantum key distribution protocols to be considered for use in free-space quantum key distribution, the effects of turbulent atmosphere need to be negated.
Here we will present an overview of a project funded by the UK Quantum Communications Hub. This project investigated the implementation of a time-bin optical receiver1 and novel single-photon avalanche diode (SPAD) spatial array technology. The receiver was designed to give high performance in the event of multimode free-space channels and pointing-and-tracking errors. The implementation of the SPAD array was proposed to enable us to simultaneously measure quantum bit information and the spatial position of the beam. The presentation will include the optical receiver concept design, and a comparison of the performance of the receiver over a range of angles-of-incidence for single and multi-mode signals.
References
1. Jin, J. et al. Demonstration of analyzers for multimode photonic time-bin qubits. Phys. Rev. A 97, 1–10 (2018).

Period	9 Oct 2018
Event title	Quantum Photonics Technologies for Space
Event type	Workshop
Conference number	COST Action CA15220 Meeting
Location	Bern, Switzerland
Degree of Recognition	International