Preserving quantum states using inverting pulses: A super-zeno effect

We construct an algorithm for suppressing the transitions of a quantum mechanical system, initially prepared in a subspace P of the full Hilbert space of the system, to outside this subspace by subjecting it to a sequence of unequally spaced short-duration pulses. Each pulse multiplies the amplitude of the vectors in the subspace by -1. The number of pulses required by the algorithm to limit the leakage probability to epsilon in time T increases as Texp[root log(T-2/epsilon)], compared to T-2 epsilon(-1) in the standard quantum Zeno effect.