Coherent phase sampling protocol for fast single-shot Rydberg electrometry in pulsed microwave sensing

Rydberg electrometry via steady-state spectral shifts is bandwidth-limited by microsecond-scale atomic relaxation. We propose a coherent phase sampling protocol that interrogates transient dynamics, overcoming this limit. In a four-level Rydberg atom, a dark state is prepared, followed by microwave-only evolution for nanosecond-scale phase accumulation, then read out via a probe transient. Our analytical and numerical results show that the resulting differential signal follows ΔI∝ sin2(Ωmτ/2), directly encoding the microwave field strength Ωm and evolution time τ. Optimal timing maximizes sensitivity. This scheme achieves a single-shot measurement time of ∼150 ns—an order of magnitude faster than the microsecond relaxation limit of conventional steady-state methods and offers competitive sensitivity. Experimental feasibility is discussed. This work shifts the paradigm from steady-state to transient readout, enabling fast single-shot Rydberg electrometry for pulsed radar and transient signal capture.