  Four stroke Otto refrigerator cycles with no classical analogue are studied.
Extremely short cycle times with respect to the internal time scale of the
working medium characterize these refrigerators. Therefore these cycles are
termed sudden. The sudden cycles are characterized by the stable limit cycle
which is the invariant of the global cycle propagator. During their operation
the state of the working medium possesses significant coherence which is not
erased in the equilibration segments due to the very short time allocated. This
characteristic is reflected in a difference between the energy entropy and the
Von Neumann entropy of the working medium. A classification scheme for sudden
refrigerators is developed allowing simple approximations for the cooling power
and coefficient of performance.
