Terahertz Coherent Control of a Landau-Quantized Two-Dimensional   Electron Gas
  We demonstrate coherent control of cyclotron resonance (CR) in a two-dimensional electron gas (2DEG). We use a sequence of terahertz pulses to control the amplitude of CR oscillations in an arbitrary fashion via phase-dependent coherent interactions. We observe a self-interaction effect, where the 2DEG interacts with the terahertz field emitted by itself within the decoherence time, resulting in a revival and collapse of quantum coherence. These observations are accurately describable using {\em single-particle} optical Bloch equations, showing no signatures of electron-electron interactions, which verifies the validity of Kohn's theorem for CR in the coherent regime. 
T. Arikawa, X. Wang, D. J. Hilton, J. L. Reno, W. Pan, J. Kono
cond-mat.mes-hall