Negative Permeability in Atomic and Molecular Systems at Microwave Frequency

A new mechanism for realizing negative permeability with a three-level ladder-type atomic (or molecular) system at microwave frequency is suggested. The explicit expressions for the magnetic permeability of both steady and transient cases are presented. Compared with the previous schemes to realize negative permeability within the framework of classical electromagnetic theory, the most remarkable feature in the present mechanism is that it can realize the isotropic material with negative permeability. Such a permeability can be controllably manipulated by external coupling fields and could lead to potential applications in quantum optical devices.