Microwave electric field measurement using frequency modulation spectroscopy in Rydberg atoms vapor cells

We recently proposed a method to detect weak microwave electric field ~8µV/cm with sensitivity ~ 30 µV cm−1Hz−1/2 [Nat. Phys. 8, 819 (2012)]. This technique is based on Rydberg atoms using the concept of electromagnetically induced transparency in room temperature vapor cells. Here we show that frequency modulation spectroscopy with active control of residual amplitude modulation improves the read out signal-to-noise. The method has the potential for high sensitivity and can be self-calibrated.