Concept for single-satellite global quantum key distribution using a solid state quantum memory

We present a mission concept for generating secure keys for encryption using a single satellite to perform quantum key distribution between two ground stations anywhere on earth, without the satellite being a trusted node. Our concept is enabled by an on-board quantum memory. The proposed memory technology is based on rare-earth ion doped crystals; a family of materials that show great promise as building blocks for practical quantum information processing devices, having demonstrated coherence times comparable to the orbit period of a LEO satellite. We develop a model to quantify the rate at which a secure key can be generated, and for an example orbit connecting hypothetical ground stations in Adelaide and Brussels, we analyse the connection opportunities and their temporal distribution throughout one year. We perform a trade-off comparing two different systems for the memory – based on either Europium or Erbium dopant – and deduce that the storage capacity that is required for this concept to work is ~10⁹ and 10¹⁰ bits respectively. Finally, we discuss how these storage requirements could be achieved along with some system architecture for operating the memory in space, and conclude that the mission concept is indeed feasible.