Microwave-Field Sensing via Rydberg Entangling-Gate Dynamics

Microwave-induced couplings to nearby Rydberg levels are usually regarded as a source of gate imperfections in neutral-atom quantum processors. Here we show that the same mechanism can instead be exploited as a metrological resource for microwave electrometry. We consider a laser-driven Rydberg controlled-Z gate subjected to an additional microwave coupling during the gate operation. The microwave field modifies the gate dynamics through coherent population leakage into an auxiliary Rydberg state, imprinting its amplitude and detuning onto the final two-qubit state. We characterize this response through the output-state fidelity, quantum Fisher information, and classical Fisher information. The results reveal parameter regimes in which enhanced sensitivity of the gate dynamics to microwave perturbations gives rise to increased estimation precision. Representative Rb and Cs implementations are used to illustrate the generality of the approach and to provide concrete sensitivity estimates. More broadly, our results demonstrate that calibrated quantum-gate dynamics can serve as a metrological resource, suggesting a gate-based sensing paradigm at the interface between quantum information processing and quantum sensing.