Suppression of spin-exchange decoherence for zero-field parametric modulation magnetometers

The zero-field atomic magnetometer is a type of high-sensitivity and miniaturized quantum sensing instrument, typically using continuous radio-frequency fields for parametric modulation to extract weak magnetic signals. However, this modulation induces additional spin-exchange relaxation that degrades spin coherence. Here we report a weak bias magnetic field-assisted pulsed field modulation scheme that significantly suppresses spin-exchange decoherence. The pulsed magnetic field reduces asynchronous phase accumulation by shortening the interaction time between the modulation field and the atomic spin ensemble, while the perpendicular bias field induces spin Larmor precession to periodically average modulation-induced relaxation, thereby suppressing the spin-exchange relaxation rate by a factor approximately equal to the pulse duty cycle. We develop a perturbative spin dynamics model to analyze the spin polarization response under this modulation. The experimental results demonstrate that this scheme overcomes the limitation imposed by the duty cycle threshold, suppresses the spin-exchange relaxation rate by more than 50%, and significantly enhances the magnetic response and sensitivity compared to conventional continuous modulation. This method can be extended to various alkali-metal spin systems relying on radio-frequency field operation, providing a new scheme for reducing modulation-induced spin-exchange decoherence.