  The composite rotation approach has been used to develop a range of robust
quantum logic gates, including single qubit gates and two qubit gates, which
are resistant to systematic errors in their implementation. Single qubit gates
based on the BB1 family of composite rotations have been experimentally
demonstrated in a variety of systems, but little study has been made of their
application in extended computations, and there has been no experimental study
of the corresponding robust two qubit gates to date. Here we describe an
application of robust gates to Nuclear Magnetic Resonance (NMR) studies of
approximate quantum counting. We find that the BB1 family of robust gates is
indeed useful, but that the related NB1, PB1, B4 and P4 families of tailored
logic gates are less useful than initially expected.
