Phase Control of Electromagnetically Induced Transparency in a Cyclic Three-Level System

We present a theoretical study on the spectral linewidth of electromagnetically induced transparency (EIT) in a cyclic three-level atomic system coupled by double coupling fields and a microwave field. The absorption profiles are obtained by a weak probe field scanning corresponding transition. It is shown that for definite Rabi frequencies of interacting fields the spectral linewidth of transparency windows depends on the relative phase between two coupling fields. In particular, as the relative phase of the double coupling fields approaches to , the linewidth narrows distinctly. This proposes a way to controlling spectral width of EIT by changing the relative phase between two fields.