Electromagnetically Induced Transparency - Slow Light and Stopped Light

Slow Light and Stopped Light

It is important to realize that EIT is only one of many diverse mechanisms which can produce slow light. The Kramers–Kronig relations dictate that a change in absorption (or gain) over a narrow spectral range must be accompanied by a change in refractive index over a similarly narrow region. This rapid and positive change in refractive index produces an extremely low group velocity. See for this the comprehensive review on this subject in. The first experimental observation of the low group velocity produced by EIT was by Boller, Imamoglu, and Harris at Stanford University in 1991 in strontium. The current record for slow light in an EIT medium is held by Budker, Kimball, Rochester, and Yashchuk at U.C. Berkeley in 1999. Group velocities as low as 8 m/s were measured in a warm thermal Rubidium vapor.

Stopped light, in the context of an EIT medium, refers to the coherent transfer of photons to the quantum system and back again. In principle, this involves switching off the coupling beam in an adiabatic fashion while the probe pulse is still inside of the EIT medium. There is experimental evidence of trapped pulses in EIT medium. In authors created stationary light pulse inside the atomic coherent media. In 2009 researchers from Harvard University and MIT demonstrated few-photon optical switch for quantum optics based on the slow light ideas