N. Linden et al., Pulse sequences for NMR quantum computers: how to manipulate nuclear spinswhile freezing the motion of coupled neighbours, CHEM P LETT, 305(1-2), 1999, pp. 28-34
We show how to divide a coupled multi-spin system into a small subset of 'a
ctive' spins that evolve under chemical shift or scalar coupling operators
and a larger subset of 'spectator' spins which are returned to their initia
l states, as if their motion had been temporarily frozen. This allows us to
implement basic one- and two-qubit operations from which general operation
s on N-qubits can be constructed, suitable for quantum computation. The pri
nciples an illustrated by experiments on the three coupled protons of 2,3-d
ibromopropanoic acid, but the method is applicable to any spin-1/2 nuclei a
nd to systems containing arbitrary numbers of coupled spins. (C) 1999 Elsev
ier Science B.V. All rights reserved.