Parametric and nonparametric magnetic response enhancement via electrically induced magnetic moments

The realization of negative refraction in atomic gases requires a strong magnetic response of the atoms. Current proposals for such systems achieve a parametric enhancement of the magnetic response by one inverse power of the fine-structure constant α, but still rely on high gas densities. To enable further enhancement, here we study in detail the magnetic and electric response to a probe field interacting with three-level atoms in ladder configuration. In our first model, the three transitions are driven by a control field and the electric and magnetic components of the probe field, giving rise to a closed interaction loop. In a reference model, the coherent driving is replaced by an incoherent pump field. A time-dependent analysis of the closed-loop system enables us to identify the different contributions to the medium response and to determine the enhancement mechanism. Based on these results, we show that in addition to the parametric enhancement of α⁻¹∼137, our system allows for a further nonparametric enhancement of the magnetic response by almost two orders of magnitude, relaxing the requirement for a high vapor density.