Probing beyond the laser coherence time in optical clock comparisons
David B. Hume, David R. Leibrandt
We develop protocols that circumvent the laser noise limit in optical clock comparisons by synchronous probing of two clocks using phase-locked local oscillators. This allows for probe times longer than the laser coherence time, avoids the Dick effect, and supports Heisenberg-limited scaling of measurement precision. We present a model for such frequency comparisons and develop numerical simulations of the protocol with realistic noise sources. This provides a route to reduce frequency ratio measurement durations by more than an order of magnitude as clock inaccuracies reach 1x10-18.