Spin transfer and coherence in coupled quantum wells
  Spin dynamics of optically excited electrons confined in asymmetric coupled quantum wells are investigated through time resolved Faraday rotation experiments. The inter-well coupling is shown to depend on applied electric field and barrier thickness. We observe three coupling regimes: independent spin precession in isolated quantum wells, incoherent spin transfer between single-well states, and coherent spin transfer in a highly coupled system. Relative values of the inter-well tunneling time, the electron spin lifetime, and the Larmor precession period appear to govern this behavior. 
M. Poggio, G. M. Steeves, R. C. Myers, N. P. Stern, A. C. Gossard, and   D. D. Awschalom