Practical Quantum Clock Synchronization Using Weak Coherent Pulses

Abstract: Establishing and maintaining a common time reference across spatially separated devices is a prerequisite for networked quantum experiments and secure communications. Classical two-way timing protocols such as Network Time Protocol (NTP) or Precision Time Protocol (PTP) are vulnerable to asymmetric channel delays and cannot provide the picosecond-level precision demanded by quantum repeater networks. We propose and numerically evaluate a quantum-enhanced clock synchronization protocol based on attenuated weak coherent pulses (WCPs) and bidirectional Hong--Ou--Mandel (HOM) interferometry. Our simulations assume telecom-band photons ($1550\,\mathrm{nm}$) with a temporal width of $10.0\,\mathrm{ns}$, a repetition rate of $f = 10\,\mathrm{MHz}$, effective mean photon number $\mu = 1.0$, detector efficiency $\eta = 85\%$, detector timing jitter of $150\,\mathrm{ps}$, and channel loss of $0.2\,\mathrm{dB/km}$. We simulate that sub-nanosecond clock-offset accuracy and precision can be achieved under these operating conditions. This work demonstrates that high-repetition-rate WCPs combined with HOM interference can provide flexible and secure quantum clock synchronization at sub-nanosecond precision.