  We present a composite pulse controlled phase gate which together with a bus
architecture improves the feasibility of a recent quantum computing proposal
based on rare-earth-ion doped crystals. Our proposed gate operation is tolerant
to variations between ions of coupling strengths, pulse lengths, and frequency
shifts, and it achieves worst case fidelities above 0.999 with relative
variations in coupling strength as high as 10% and frequency shifts up to
several percent of the resonant Rabi frequency of the laser used to implement
the gate. We outline an experiment to demonstrate the creation and detection of
maximally entangled states in the system.
