  It has been recently proved that a quantum jump may be reversed by a unitary
process provided the initial state is restricted by some conditions. The
application of such processes for preventing decoherence, for example in
quantum computers, was suggested. We shall show that in the situation when the
quantum jump is reversible it supplies no information about the initial state
additional to the information known beforehand. Therefore the reversibility of
this type does not contradict the general statement of quantum measurement
theory: a measurement cannot be reversed. As a consequence of this, the
coherence of a state (say, in a quantum computer) cannot be restored after it
is destroyed by dissipative processes having a character of measurement.
