Interplay between Zeeman Coupling and Swap Action in Spin-based Quantum   Computer Models: Error Correction in Inhomogeneous Magnetic Fields
  We consider theoretically the interplay between Zeeman coupling and exchange-induced swap action in spin-based quantum dot quantum computer models in the presence of inhomogeneous magnetic fields, which are invariably present in real systems. We estimate quantitatively swap errors caused by the inhomogeneous field, establishing that error correction would, in principle, be possible in the presence of non-uniform magnetic fields in realistic structures. 
Xuedong Hu, Rogerio de Sousa, and S. Das Sarma