Quantum key distribution with entangled photons in daylight

Andrej Krzic

Fraunhofer IOF / Airbus Netherlands

Quantum key distribution (QKD) offers means to transmit data with unprecedented security, rooted in the laws of quantum mechanics. The use of entangled photons seems particularly well suited for this purpose. The research focus in QKD has been lately increasingly moving from fundamental towards more practical aspects.

One of the main challenges for implementation over free-space channels is operation in daytime, when the receiver system inevitably collects sunlight that may be orders of magnitude stronger than the weak quantum signal. Efficient filtering is required in every available degree of freedom. Spatial filtering is further hindered by atmospheric turbulence. For this reason, the vast majority of free-space QKD experiments have been limited to nighttime, including the only successful satellite-based demonstrations to date.

In this talk, I will present my PhD work, at the heart of which is an experimental realization of entanglement-based QKD in daylight over a 1.7-km free-space link. This is followed by a more thorough investigation of the role of spatial filtering. The work concludes with a numerical simulation of a satellite-based implementation, which shows that the first daytime QKD from an orbiting satellite is within reach.