Electromagnetically induced transparency at a chiral exceptional point

Electromagnetically induced transparency, as a quantum interference effect to eliminate optical absorption in an opaque medium, has found extensive applications in slow-light generation, optical storage, frequency conversion, optical quantum memory and enhanced nonlinear interactions at the few-photon level in all kinds of systems. Recently, there has been great interest in exceptional points, a type of spectral singularity that could be reached by tuning various parameters in open systems, to render unusual features to the physical systems, such as optical states with chirality. Here we theoretically and experimentally study transparency and absorption modulated by chiral optical states at exceptional points in an indirectly coupled resonator system. By tuning one resonator to an exceptional point, transparency or absorption occurs depending on the chirality of the eigenstate. Our results demonstrate a new strategy to manipulate the light flow and the spectra of a photonic resonator system by exploiting a discrete optical state associated with a specific chirality at an exceptional point as a unique control bit. Such an approach is compatible with the state control utilized in quantum gate operation and may open up new avenues for controlling slow light using optical states for optical quantum memory and computing.