[1] Heidelberg Univ, Kirchhoff Inst Phys, Neuenheimer Feld 227, D-69120 Heidelberg, Germany
[2] Inst Polytech Paris, Lab Phys Matiere Condensee, Ecole Polytech, CNRS, F-91120 Palaiseau, France
[3] Univ Trento, INO CNR BEC Ctr, Via Sommar 14, I-138123 Trento, Italy
[4] Univ Trento, Dept Phys, Via Sommar 14, I-138123 Trento, Italy
[5] Barcelona Inst Sci & Technol, ICFO Inst Ciencies Foton, Av Carl Friedrich Gauss 3, Castelldefels 08860, Barcelona, Spain
[6] Harvard Univ, Dept Phys, Cambridge, MA 02138 USA
[7] Hebrew Univ Jerusalem, Racah Inst Phys, IL-91904 Jerusalem, Israel