Quantum computing with spin cluster qubits

The low energy states of spin cluster qubits with isotropic and anisotropic antiferromagnetic exchange interaction were studied with uniform and nonuniform coupling constants. A qubit defined in terms of the ground state doublet showed remarkable insensitiveness towards the placement and coupling anisotropy of spins within the cluster. The magnetic field and intercluster exchange resulted in the generation of one- and two-qubit quantum gates, with small operation time leakage. The inheritance of long decoherence times and short gate operation times of single spins in spin cluster qubits was also discussed.