  For the implementation of a quantum computer it is necessary to exercise
complete control over the Hamiltonian of the used physical system. For NMR
quantum computing the effectively acting Hamiltonian can be manipulated via
pulse sequences. Here we examine a register consisting of N selectively
addressable spins with pairwise coupling between each spin pair. We show that
complete decoupling of the spins is possible independent of the particular form
of the spin-spin interaction. The proposed method based on orthogonal arrays is
efficient in the sense that the effort regarding time and amount of pulses
increases only polynomially with the size N of the register. However, the
effect of external control errors in terms of inaccurate control pulses
eventually limits the achievable precision.
