Subluminal and superluminal light pulse propagation under external magnetic field in a vee-type three-level atomic medium

In this work, we investigate subluminal and superluminal light propagation in a vee-type three-level atomic medium under an external magnetic field. The dispersion and absorption behaviors are studied for the cases of absence and presence of a magnetic field. It is found that under an electromagnetically induced transparency condition, the light pulse can be switched between subluminal and superluminal propagation by ON-OFF switching of the magnetic field. Finally, the transient response of the medium is discussed, which shows that the considered scheme has potential applications in magneto-optic switching devices. In recent years, the phenomenon of electromagnetically induced transparency (EIT) [1÷2], which is generated by quantum interference between two different displacement channels and an opaque optical medium can become transparent in a probe field by applying a strong control laser field at a different frequency. The EIT effect not only reduces absorption but also enhances linear and nonlinear dispersions in the vicinity of atomic resonant frequency. One of the interesting applications of the EIT medium is that it modifies light pulse propagation through the dispersion of a medium, such as controlling and slowing down the group velocity of light, even stopping, storing, and then it retrieves light pulses [3÷5], enhances Kerr nonlinearity [6÷7], optical bistability (OB) and alloptical switching (AOS) [8÷10], formation and optical solitons propagation [11÷13], and so on. In addition to intensity-controllable absorption and dispersion properties of an EIT medium, recent studies show that the optical properties of an EIT medium are also controlled by external magnetic field and polarization of laser fields [14÷17]. In this work, we use an external magnetic field to switch from electromagnetically induced transparency to electromagnetically induced absorption (EIA), which corresponds with the propagation of light from subluminal to superluminal velocity. We investigate the influence of an external magnetic field on the absorptive and dispersive properties as well as the group index and transient behavior of the probe field, which demonstrates that the medium can be used for optical switches at a low light intensity. * E-mail: donghmhufi@gmail.com The vee-type degenerated the atomic system under the interaction of an external magnetic field as shown in Fig.1. In this scheme, the transition |1 to |3 is applied by a weak probe laser field Ep (have angular frequency ωp) with the right-circularly polarized component σ. Simultaneously, a strong coupling laser field Ec with the left-circularly polarized component σ (have angular frequency ωc) is introduced to couple the transition |1 to |2. The medium is likely to be affected by an applied longitudinal magnetic field B removing the degeneracy of the states |2 and |3, whose Zeeman shift is determined by / B B F F m g B  =  h , where μB is the Bohr magneton, gF is the Lande factor, and mF = ±1 is the magnetic quantum number of the corresponding state. The decay rates from the states |3 and |2 to |1 are given by γ31 and γ21, respectively. Utilizing the rotating-wave and the electric dipole approximations, the interaction Hamiltonian of the system in the interaction picture can be written as (with the assumption of h =1): Fig.1. Schematic diagram of a vee-type degenerated atomic system under a static magnetic field and two coupling and probe laser fields.