Extremely low frequency electric field sensing using Rydberg ionization detection

We present a method for sensing electric fields down to single Hertz frequencies using a collimated beam of rubidium Rydberg atoms. The Rydberg atoms are detected using a field ionization measurement scheme. External electric fields produce DC Stark shifts which are detected as modulations of the ion signal. This method circumvents much of the low frequency electric field screening effects typically present in warm vapor cells containing alkali-metal atoms. With this approach a sensitivity of better than 1 mV/m√Hz is achieved for frequencies above 20 Hz with a spectral noise floor of ≈0.15 mV/m√Hz.