1. Department of Physics, Harvard University, Cambridge, MA 02138, USA.
2. Department of Physics, Massachusetts Institute of Technology (MIT)–Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, MIT, Cambridge, MA 02139, USA.
3. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
4. Institute for Theoretical Atomic Molecular and Optical Physics (ITAMP), Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA.
5. Russian Quantum Center, Skolkovo, Moscow Region 143025, Russia.