[1] Austrian Acad Sci, Inst Quantum Opt & Quantum Informat, A-1010 Vienna, Austria
[2] Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria
[3] Univ Warsaw, Inst Theoret Phys, PL-00681 Warsaw, Poland
[4] NIST, Joint Quantum Inst, Gaithersburg, MD 20899 USA
[5] Univ Maryland, Gaithersburg, MD 20899 USA