Low-noise low-frequency electric-field measurement using Rydberg-atom-mediated sum-frequency mixing

Low-frequency (LF) electric-field measurements with Rydberg atoms are limited by alkali-induced cell-surface screening and excess laser-intensity noise. Here, we address these limitations using a Cs vapor cell with built-in parallel electrodes, active laser-power stabilization, and a home-built balanced detector to suppress 10 Hz-kHz intensity noise. A 15 kHz local-oscillator field is introduced to up-convert Hz-scale signals to the lower-noise kHz band through Rydberg atom-mediated sum-frequency mixing (SFM), improving the optical readout signal-to-noise ratio. The system achieves a minimum detectable electric field of 190 nV/cm within 0.5 Hz-1.006 kHz, a linear dynamic range exceeding 67 dB, and a spectral resolution of 18 mHz.