1. Laboratoire de Physique Théorique et Modélisation, CNRS UMR 8089, CY Cergy Paris Université, 95302 Cergy-Pontoise Cedex, France
2. Department of Physics, The Pennsylvania State University, University Park, PA 16802
3. Department of Physics, University of Massachusetts, Amherst, MA 01003
4. Joint Center for Quantum Information and Computer Science, National Institute of Standards and Technology/University of Maryland, College Park, MD 20742