1. Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94114 and Technical University Ilmenau, D-98684 Ilmenau, Germany
2. Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94114
3. Technical University Ilmenau, D-98684 Ilmenau, Germany
4. Department of Electrical Engineering and Computer Science, University of California, Berkeley, California 94720 and The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720
5. Department of Electrical Engineering and Computer Science, University of California, Berkeley, California 94720
6. The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720
7. School of Physics, University of the Witwatersrand, Wits 2050, Johannesburg, South Africa
8. Center for Spintronics and Quantum Computation, University of California, Santa Barbara, California 93106
9. Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands