Analytical Model of Satellite Based Entanglement Distribution

Abstract

For a global quantum communication network, we need to have long distance links over which we can distribute entangled photon pairs. Due to exponential losses, using optical fibres alone is unfeasible. Quantum repeaters extend the range of quantum networks, but intercontinental links are still unfeasible. Because of this, research has gone towards exploring space based segments, where a satellite can be used to make long-distance links by making use of the lower losses of free space transmission compared to fibre transmission. Here, we develop a general analytical model to compute the rate and fidelity of setups consisting of two ground stations connected by a satellite in orbit. We consider three different schemes: a direct downlink and two memory assisted schemes where the satellite is used as a quantum repeater, in an uplink and a downlink. Combining orbital mechanics for the satellite with a detailed model for transmission probability, allows us to track what happens to the rate and fidelity at any point in time. The generality of the model allows for a broad applicability, fitting to many different setups. We apply our model to different setups by tuning the different parameters and identify that the rate of the protocol will benefit most from increasing the multimode capacity of our assisting quantum memory and that the fidelity is most benefited by a good entanglement swap in the memory assisted schemes. If we have small links, bad memories or a bad entanglement swap, the direct downlink protocol will be the best choice, but for an intercontinental link we will need our memory assisted schemes.