Abstract :
In recent work we have demonstrated a fundamentally new approach for electric (E) field measurements (Holloway et al., IEEE Trans on AP 12, 6169–6182, 2014; Sedlacek et al., Nature Phys, 8, 819, 2012). The new approach is based on the interaction of RF-fields with Rydberg atoms, where alkali atoms are excited optically to Rydberg states and the applied RF-field alters the resonant state of the atoms. For this technique, the Rydberg atoms are placed in a glass vapor cell. This vapor cell acts like an RF-to-optical transducer, converting an RF E-field to an optical frequency response. The approach utilizes the concept of electromagnetically induced transparency (EIT), where the RF transition in the four-level atomic system causes a split of the transition spectrum for the probe laser. This splitting is easily measured and is directly proportional to the applied RF field amplitude (through Planks constant and the dipole moment of the atom). Therefore, by measuring this splitting we get a direct measurement of the RF E-field strength. The significant dipole response of Rydberg atoms over the GHz regime indicates that this technique can be used for traceable measurements over a large frequency band including 1 GHz to 500 GHz (Holloway et al., IEEE Trans on AP 12, 6169–6182, 2014). The new approach has several benefits over existing techniques, including, 1) a direct SI units linked E-field measurement, 2) a self-calibrating measurement due to atomic resonances, 3) a technique that is independent of current approaches, 4) a very small spatial resolution: optical fiber and chip-scale, and 5) a technique with vastly improved sensitivity and dynamic range over current E-field methods.
