  We investigate the quantum-classical transition in the delta-kicked rotor and
the attainment of the classical limit in terms of measurement-induced
state-localization. It is possible to study the transition by fixing the
environmentally induced disturbance at a sufficiently small value, and
examining the dynamics as the system is made more macroscopic. When the system
action is relatively small, the dynamics is quantum mechanical and when the
system action is sufficiently large there is a transition to classical
behavior. The dynamics of the rotor in the region of transition, characterized
by the late-time momentum diffusion coefficient, can be strikingly different
from both the purely quantum and classical results. Remarkably, the early time
diffusive behavior of the quantum system, even when different from its
classical counterpart, is stabilized by the continuous measurement process.
This shows that such measurements can succeed in extracting essentially quantum
effects. The transition regime studied in this paper is accessible in ongoing
experiments.
