Proper magnetic fields for nonadiabatic geometric quantum gates in NMR

In a scheme of nonadiabatic purely geometric quantum gates in nuclear magnetic resonance(NMR) systems we propose proper magnitudes of magnetic fields that are suitable for an experiment. We impose a natural condition and reduce the degree of freedom of the magnetic fields to the extent. By varying the magnetic fields with essentially one-dimensional degree of freedom, any spin state can acquire arbitrary purely geometric phase \phi_{g}=-2\pi(1-cos{theta}), 0 < cos{\theta} < 1. This is an essential ingredient for constructing universal geometric quantum gates.