An Entangled Optical Clock Node for Fifth-Coordinate Phase Synchronisation

This paper presents the design of a clock node that distributes synchronisation by entangled photon pairs rather than by classical pulses, and computes what the design can deliver under stated component assumptions. A periodically poled source produces photon pairs at 1550 nm at a pair rate of 10 MHz; with an overall detection efficiency of 0.62 and detector timing jitter of 50 ps, jitter averaging over the pairs detected in one second gives a synchronisation offset of 20.1 fs between two nodes. Two-photon interference visibility is taken as 94.0 percent, the phase-lock bandwidth as 100.0 kHz, and a random-walk holdover model gives 1.205 ps of accumulated offset after one hour without correction. The node is intended as the timing reference for instruments that read a phase associated with the fifth coordinate, where a shared phase origin matters more than absolute frequency accuracy. The design is simulated, not measured: no hardware was built, and every figure comes from the accompanying computation.