Quantum sensing of low-frequency electric signal enabled by modulated auxiliary field in Rydberg atoms

Low-frequency (LF) electric field sensing is critical for applications like space science and geophysical surveys. Traditional Rydberg atom sensors rely on static DC bias fields, typically generated by internal electrodes or plasmas, which suffer from calibration drift, poor long-term stability, and environmental sensitivity. This paper investigates whether an AC-modulated auxiliary field can replace these static fields to provide a more robust, electrode-free sensing architecture.

The authors propose a quantum frequency mixing (QFM) strategy. By applying an AC auxiliary field alongside the weak LF signal field, the atoms experience a time-dependent second-order Stark shift. This shift contains a cross-term proportional to the product of the signal and auxiliary amplitudes, effectively mapping the LF signal onto higher-frequency sidebands. This signal is then read out using a weak-measurement-enhanced polarization detection scheme, which translates the energy shift into a measurable change in probe laser intensity while suppressing technical noise.

The experimental implementation achieved a sensitivity of 7.5 μV/(cm·Hz^1/2) at 5 kHz and a minimal detectable field of 0.26 μV/cm with a 1000-second integration time. The authors demonstrated that the system is stable and calibration-friendly, as it avoids the use of internal electrodes. Furthermore, they showed that using multiple auxiliary frequency components allows for signal combination techniques that further improve the signal-to-noise ratio. The system's performance is currently limited by the shielding effect of the glass cell walls and the finite bandwidth of the EIT response, though the authors suggest that synchronous modulation of the coupling laser could mitigate these bandwidth constraints.