A Spin-Memory Quantum Repeater Node Stabilised by a Torsion Phase Reference

Long-distance quantum communication fails by loss: a photon's survival probability falls exponentially with fibre length, so direct transmission cannot span continental distances at useful rates. Repeater nodes divide the route into short links, establish entanglement on each, store it in matter memories, and join the links by swapping. This paper designs such a node around spin memories with one-second coherence and computes the chain performance for eight links of 25 km. The elementary link success probability is 0.1138, giving Bell pairs on a single link at 113842 Hz for a megahertz attempt rate, and an end-to-end rate of 238.7 Hz after swapping across all eight links. A torsion phase reference is specified to hold the interferometric phase of the swapping stations. All figures are computed; no link has been operated.