Zusammenfassung
We consider a quantum mechanical state initially in a subspace
$P$ of the full Hilbert space of the system and subjected to a
sequence of appropriately spaced short-duration pulses. In between the pulses,
the evolution of the system is governed by its Hamiltonian. The pulse adds a
phase $\pi$ to the vectors in the subspace $P$. We construct a
sequence of $N$ pulses within a finite time interval $T$ such that the
probability of finding the system outside $P$ at $T$ can be made as
small as $2^- (łog_2 N)^2$, for large $N$.
Nutzer