Electromagnetically induced transparency in semiconductor quantum wells

Nonradiative quantum coherences between states that are not directly dipole-coupled can lead to quantum interference in optical transitions. Destructive interference induced by nonradiative quantum coherence in a three-level system can render an otherwise opaque medium nearly transparent, leading to the phenomenon of electromagnetically induced transparency (EIT).^1-3 EIT and EIT-related processes provide a powerful and effective mechanism for controlling and manipulating light with nonradiative quantum coherences. Recent successes include the reduction of the group velocity of light by many orders of magnitude, the reversible storage of light as a stationary spin coherence, and the generation of entangled photon pairs with controllable delays.^4-13 Other well-known phenomena closely related to EIT include coherent population trapping, lasing without inversion, and stimulated Raman adiabatic passage.^1-3 While most EIT studies have thus far been carried out in atomic or atomic-like systems, the basic concept of destructive quantum interference induced by nonradiative quantum coherence can also be applied to extended optical excitations such as excitons in semiconductors.^14-24 EIT studies in semiconductors can further deepen our understanding of quantum coherence and interference in solids and can potentially open up new avenues for applications of EIT and EITrelated phenomena.