Measurement of microwave electric field based onelectromagnetically induced transparency by using cold Rydberg atoms br

Microwave electric fields are measured by using cold Rydberg atoms. We obtain spindle-shaped cold atomicclouds in a magneto-optical trap and then pump the cold atoms to quantum state 5S1/2, F = 2, mF = 2 byusing an optical-pump laser. We obtain the Rydberg electromagnetic induction transparency (EIT) spectrumpeak with narrow linewidth by the low temperature and small residual Doppler broadening. The results showthat the typical EIT linewidth with 16 mu K cold atoms is about 460 kHz which is 15 times narrower than that of7 MHz obtained in the thermal vapor cell. The microwave electric field amplitude is measured by Autler-Townes splitting (EIT-AT splitting) in the cold atoms at frequencies of 9.2, 14.2 and 22.1 GHz, receptively. Theresults show that there is a good linear relationship between the EIT-AT splitting interval and the microwaveelectric field amplitude. The lower limit of the microwave electric field amplitude that can be measured in thelinear region can reach as low as 222 mu V/cm, which is about 22 times larger than the lower limit in thetraditional thermal vapor cell about of 5 mV/cm. The improvement of the lower limit by EIT-AT splittingmethod is roughly proportional to the narrowing EIT line width by cold atom samples. This demonstrates thatbenefiting from the smaller residual Doppler effect and the narrower EIT linewidth in cold atoms, the cold atomsystem is more advantageous in the experimental measuring of the weak microwave electric field amplitude byusing the EIT-AT splitting method. This is of great benefit to the absolute calibration of very weak microwaveelectric fields. Furthermore, the lower limit of the microwave electric field amplitude that can be measured issmaller than 1 mu V/cm by using the change of transmittance of the prober laser at the EIT resonance, and thecorresponding sensitivity can reach 1 mu Vmiddotcm-1middotHz-1/2. These results demonstrate the advantages of cold atomicsample in microwave electric field measurement and its absolute calibration