Magnetic-field-engineered coherent perfect absorption and transmission

An experimental work [W. J. Wan, Y. D. Chong, L. Ge, H. Noh, A. D. Stone, and H. Cao, Science 331, 889 (2011)] showed that a resonator that contains a loss medium instead of a gain medium enables coherent perfect absorption (CPA) by interference. Here, we propose an alternative approach to realize such a CPA and coherent perfect transmission (CPT) as well as the switching between CPA and CPT in a cavity quantum electrodynamics (CQED) system by applying an external magnetic field. The proposed CPA and CPT scheme is based on the magnetically induced transparency (MIT) configuration, instead of the conventional electromagnetically induced transparency configuration, which offers a sensitive method to tune CPA and CPT and also is conducive to the flexible control of the CPA and CPT scheme. Under the linear and nonlinear excitation regimes, we derive the approximate analytical solutions of the cavity-output power and the CPA criteria of the CQED system, and find that the CPA can occur at different frequencies in both regimes. In the nonlinear excitation regime, the relationship between the cavity-output power and the cavity-input power can show a bistable characteristic by the control of the static magnetic field, and the CPA point is near the turning point of the cavity-input power on the bistable return hysteresis curve. Furthermore, the line shape and the threshold value for optical bistability can be flexibly controlled by varying the magnetic field under experimentally accessible conditions, thus the magnetic field can well tune the CPA. Also, we compare the analytical and numerical results of the cavity-output power in the nonlinear excitation regime, and they are in good agreement. Our results show that the CQED system based on the MIT configuration can be used as a perfect absorber or nearly perfect transmitter, which may have practical applications in optical logic and optical communication devices.