An Entanglement-Swapping Relay for Long-Baseline Clock Distribution

Distributing entanglement across a baseline longer than a single low-loss span requires swapping: entanglement created independently on two halves of the route is joined by a Bell measurement at the middle station. This paper designs a swapping relay for clock-distribution baselines and computes its throughput. With elementary link success probability 0.08 on each half and a linear-optics Bell analyser of efficiency 0.5 with detector efficiency 0.9, the swapping success probability is 2.59e-03 and the relay delivers swapped pairs at 25920 Hz at a ten megahertz attempt rate. The relay holds no memory: it is the memoryless middle station of a longer architecture, suitable where baselines are moderate and rates, rather than distance records, are the goal. Figures are computed; no relay has been operated.