Stabilization of Quantum Computer Calculation Basis by Qubit Encoding in   Virtual Spin Representation
  It is proposed to map the quantum information qubit not to individual spin 1/2 states, but to the collective spin states being eigenfunctions of the Hamiltonian including spin-spin interactions, which may be not small. Such an approach allows to introduce more stable calculation basis for quantum computer based on the solid state NMR systems. 
A.R. Kessel