Decoherence and Zeno time in quantum computations

We analyze the short-time behaviour of the survival probability in the frame of the Friedrichs model for different formfactors. We have shown that the probability may not be quadratic for the short times while the quantum Zeno effect (QZE) still exists in this case. We have found that the time when the QZE could be observed is much smaller than usually assumed. We have studied the anti-Zeno era and have estimated its duration. Related decoherence processes are also discussed.