  Electromagnetically induced transparency (EIT) is a phenomenon that can
provide strong and robust interfacing between optical signals and quantum
coherence of electronic spins. In its archetypical form, mainly explored with
atomic media, it uses a (near-)homogeneous ensemble of three-level systems, in
which two low-energy spin-1/2 levels are coupled to a common optically excited
state. We investigate the implementation of EIT with c-axis divacancy color
centers in silicon carbide. While this material has attractive properties for
quantum device technologies with near-IR optics, implementing EIT is
complicated by the inhomogeneous broadening of the optical transitions
throughout the ensemble and the presence of multiple ground-state levels. These
may lead to darkening of the ensemble upon resonant optical excitation. Here,
we show that EIT can be established with high visibility also in this material
platform upon careful design of the measurement geometry. Comparison of our
experimental results with a model based on the Lindblad equations indicates
that we can create coherences between different sets of two levels
all-optically in these systems, with potential impact for RF-free quantum
sensing applications. Our work provides an understanding of EIT in multi-level
systems with significant inhomogeneities, and our considerations are valid for
a wide array of defects in semiconductors.
