Electromagnetically induced invisibility

The recent exciting development of invisibility cloaks, has attracted intense attention and discussion. Theoretically, the cloaks are constructed by coordinate transform methods. The object inside the cloak is invisible to the outside observer, because the light is excluded from the object and the exterior field is not perturbed. The invisibility of the linearly radially transformed cylindrical and spherical cloaks has been confirmed by both numerical calculations and analytic solutions.

Experimentally, the invisibility cloak with simplified material parameters has been implemented by Schurig et.al at the microwave frequence. Here, instead of a complete cloak, we will consider a cloak to mimic a at ground plane. This type of cloak is far less demanding in terms of the range of refractive index the cloaking medium has to achieve, it also has the advantage that the parameters of the cloak need not be singular and can be isotropic. The proposed carpet cloaks have been verfied and experimentally demonstrated in both microwave and optical frequency range. These approaches all include the quasi-conformal transformation for the advantage of reducing anisotropy of the cloak. However, the material for the carpet cloak is still inhomogeneous and needs to be carefully designed to obtain the required spatial distribution of its parameters.

Metamaterials are usually used as the building blocks for transformation optics as they can attain a wide range of permittivity and permeability. However, scaling down the magnetic resonating structures for the metamaterials to optical frequencies causes severe absorption. This has led us to consider instead the effect of electromagnetically induced transparency (EIT) in magneto-electric media, the so-called chiral media. It has been shown that these media allow us fine control over the value of the refractive index by the strength of the coherent coupling and the detuning of the atomic energy levels. Simultaneously, a quantum interference effect, the EIT, strongly suppresses absorption.