  We investigate inflation driven by the evolution of highly excited quantum
states within the framework of out of equilibrium field dynamics. The
self-consistent evolution of these quantum states and the scale factor is
studied analytically and numerically. It is shown that the time evolution of
these quantum states lead to two consecutive stages of inflation under
conditions that are the quantum analogue of slow-roll. The evolution of the
scale factor during the first stage has new features that are characteristic of
the quantum state. During this initial stage the quantum fluctuations in the
highly excited band build up an effective homogeneous condensate with a
non-perturbatively large amplitude as a consequence of the large number of
quanta. The second stage of inflation is similar to the usual classical chaotic
scenario but driven by this effective condensate. The excited quantum modes are
already superhorizon in the first stage and do not affect the power spectrum of
scalar perturbations. Thus, this novel scenario provides a field theoretical
justification for chaotic scenarios driven by a classical homogeneous scalar
field of large amplitude.
