[1] Univ Texas Austin, Phys, Austin, TX 78712 USA
[2] Ludwig Maximilians Univ Munchen, Munich, Germany
[3] Max Planck Inst Quantum Opt, Garching, Germany
[4] Virginia Tech, T Marshall Hahn Chair Phys, Blacksburg, VA USA
[5] Virginia Tech, Ctr Quantum Informat Sci & Engn, Blacksburg, VA USA
[6] Indian Inst Sci IISc, Bangalore, India
[7] Univ Calif Berkeley, Berkeley, CA USA
[8] CNRS Thales, Palaiseau, France
[9] Chinese Acad Sci, Natl Astron Observ China, Beijing, Peoples R China