[1] Univ Copenhagen, Dept Math Sci, QMATH, DK-2100 Copenhagen O, Denmark
[2] Delft Univ Technol, QuTech, Lorentzweg 1, NL-2628 CJ Delft, Netherlands
[3] Delft Univ Technol, Kavli Inst Nanosci, Lorentzweg 1, NL-2628 CJ Delft, Netherlands
[4] Harvard Smithsonian Ctr Astrophys, ITAMP, Cambridge, MA 02138 USA
[5] Harvard Univ, Dept Phys, Cambridge, MA 02138 USA
[6] Humboldt Univ, Dept Phys, D-12489 Berlin, Germany
[7] Univ Copenhagen, Niels Bohr Inst, Ctr Hybrid Quantum Networks Hy Q, DK-2100 Copenhagen O, Denmark