Tackling Systematic Errors in Quantum Logic Gates with Composite   Rotations
  We describe the use of composite rotations to combat systematic errors in single qubit quantum logic gates and discuss three families of composite rotations which can be used to correct off-resonance and pulse length errors. Although developed and described within the context of NMR quantum computing these sequences should be applicable to any implementation of quantum computation. 
H.K. Cummins, G. Llewellyn and J.A. Jones