摘要
We propose an all-optical-control scheme to simultaneously realize parity-time (PT )-symmetric and PT -antisymmetric susceptibilities along the propagation direction of light by applying an external magnetic field. Through the light-atom interaction within a double-Λ configuration, the resulting position-dependent susceptibilities for the interacting fields can be manipulated through the relative phase between them. In particular, for the probe field, one can switch its refractive index from the PT -symmetry to PT -antisymmetry by just varying the phase. Based on the quantum interference among transition channels in a closed loop, analytical formulas are also derived to illustrate the conditions for PT -symmetry and PT -antisymmetry.