  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.
