1. Laboratoire Matériaux et Phénomènes Quantiques Université Paris Diderot—Paris 7 CNRS—UMR 7162 Bâtiment Condorcet 75205 Paris Cedex 13 France
2. Institute of Quantum Electronics ETH Zürich CH‐8093 Zürich Switzerland
3. Key Laboratory of Artificial Structures and Quantum Control Department of Physics Shanghai Jiao Tong University Shanghai 200240 China