We report an experimental observation of narrow and high-contrast spectra, which are induced by interacting dark resonances and have been predicted in Phys. Rev. A 60, 3225 (1999). Spectra are measured with cold ${}^{87}\mathrm{Rb}$ atoms produced by a magneto-optical trap. In this experimental system, a coupling laser and a weak probe laser form a three-level Λ-type configuration of electromagnetically induced transparency (EIT); a microwave drives a magnetic-dipole transition between the fourth level and the ground state that is coupled with the excited state by the coupling laser. The observed spectral profile of probe absorption exhibits a very sharp peak emerging inside a narrow EIT dip. Such spectral feature provides more opportunities in manipulating atomic-optical response.

• Received 12 June 2001

DOI:https://doi.org/10.1103/PhysRevA.64.053806