  Nature, in the form of dissipation, inevitably intervenes in our efforts to
control a quantum system. In this talk we show that although we cannot, in
general, compensate for dissipation by coherent control of the system, such
effects are not always counterproductive; for example, the transformation from
a thermal (mixed) state to a cold condensed (pure state) can only be achieved
by non-unitary effects such as population and phase relaxation.
