Vapor Cell Rydberg Electrometry with Time-Separated Fields

Alkali atoms in highly-excited Rydberg states have large transition electric dipole moments and provide a promising method for detection of very weak electromagnetic fields. The traditional approach for Rydberg electrometry is based on electromagnetically-induced transparency (EIT) and detection of Autler-Townes splitting associated with an applied microwave field resonant between two Rydberg states. We describe a new method for microwave field sensing consisting of separate excitation, quantum evolution and detection steps. The atoms are first excited to a Rydberg state and lasers are turned off. A weak microwave field and a reference field are applied to cause their evolution between two Rydberg states. Then the population remaining in the first Rydberg state is determined by measuring probe laser transmission. This stepwise process allows one to eliminate decohence mechanisms associated with optical transitions and Doppler broadening from the coherent evolution between two Rydberg states and easily obtain coherence times in excess of 1 μsec. Quantum pulse sequences, such as Ramsey interferometry and microwave spin echo can be used to further increase sensitivity and study decoherence properties of Rydberg states. In addition, we use a multi-pass cell to optimize the conditions for sensing by increasing the atom path length for the probe laser and the intensity of the coupling laser. These new techniques can dramatically increase the sensitivity and utility of Rydberg electrometry.