A tunable broadband microwave absorber based on coherent population trapping

Abstract

A scheme is proposed for a tunable broadband microwave absorber using a four-level Rydberg atom system with competition between electromagnetically induced transparency (EIT) and coherent population trapping (CPT). Two laser fields drive the Rydberg atoms from the ground state to a Rydberg state, forming a cascade-type EIT/CPT system. When a microwave (MW) field couples the Rydberg transition, a strong MW absorption peak appears. A narrow band MW absorber could be obtained via EIT, however, using CPT, the MW absorption spectrum can be significantly broadened and enhanced to have a bandwidth about ten times larger than that obtained with EIT and whose peak value can also be enhanced by a factor of ten, based on simulation.