  In this article we analyze spin dynamics for electrons confined to
semiconductor quantum dots due to the contact hyperfine interaction. We compare
mean-field (classical) evolution of an electron spin in the presence of a
nuclear field with the exact quantum evolution for the special case of uniform
hyperfine coupling constants. We find that (in this special case) the
zero-magnetic-field dynamics due to the mean-field approximation and quantum
evolution are similar. However, in a finite magnetic field, the quantum and
classical solutions agree only up to a certain time scale t<\tau_c, after which
they differ markedly.
