  Resonant dipole-dipole interaction (RDDI) is ubiquitous in light-matter
interacting systems and is responsible for many fascinating properties of
collective radiations. Here we theoretically investigate the role of RDDI in
electromagnetically induced transparency (EIT). The resonant dipole-dipole
interactions manifest in the cooperative spontaneous emission of the probe
light transition, which give rise a broadened linewidth and associated
collective frequency shift. This cooperative linewidth originates from the
nonlocal and long-range RDDI, which can be determined by the atomic density,
optical depth, and macroscopic length scales of the atomic ensemble. We present
that EIT spectroscopy essentially demonstrates all-order multiple scattering of
RDDI. Furthermore, we find that EIT transparency window becomes narrower as the
cooperative linewidth increases, which essentially reduces the storage
efficiency of slow light as EIT-based quantum memory application.
