[1] ETH, CH-8093 Zurich, Switzerland
[2] ETH, Computat Lab, CH-8092 Zurich, Switzerland
[3] Microsoft Corp, Res, Santa Barbara, CA 93106 USA
[4] Univ Calif Santa Barbara, Kavli Inst Theoret Phys, Santa Barbara, CA 93106 USA
[5] Rhein Westfal TH Aachen, Inst Theoret Phys C, D-52056 Aachen, Germany
[6] Univ Innsbruck, Inst Theoret Phys, A-6020 Innsbruck, Austria
[7] Austrian Acad Sci, Inst Quantum Opt & Quantum Informat, A-6020 Innsbruck, Austria