Quantum communication with satellites in curved spacetime

Quantum communication aims at sharing secure information, that is protected from malicious attacks by the laws of physics, between interested parties. In recent years, space-based satellite links that exchange photons through empty space have been viewed as good candidates to build a quantum communication network. This approach overcomes the fundamental distance limitations inherent to fibre-based networks, potentially extending the network to arbitrary distances, and guarantees secure communications around the globe that would be difficult to physically attack. The Chinese Academy of Sciences has recently launched the first dedicated satellite for quantum communication, that will be used for a myriad of different applications. Regardless of the fact that gravity is unavoidable in space, the effects of gravity on quantum communication protocols have so far been ignored.

I have recently closed this gap by using tools from quantum field theory in (weakly) curved spacetime to correctly incorporate the effects of the Earth’s spacetime curvature on photon propagation between a source and a satellite. I will discuss my results, which show that: (i) quantum communication can be less secure if gravitational effects on propagating photons are not considered; (ii) gravitational effects on the frequency distribution or polarisation of propagating photons can be used to measure precisely distances and the mass of the Earth; (iii) the effects of the rotation of our planet can also be included.

Future work and outlook will also be discussed.