[1] Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria
[2] Austrian Acad Sci, Inst Quantum Opt & Quantum Informat, A-6020 Innsbruck, Austria
[3] PlanQC GmbH, D-85748 Garching, Germany
[4] CALTECH, Dept Phys, Pasadena, CA 91125 USA
[5] CALTECH, Inst Quantum Informat & Matter, Pasadena, CA 91125 USA