[1] Max Planck Inst Struct & Dynam Matter, D-22761 Hamburg, Germany
[2] Univ Oxford, Dept Phys, Clarendon Lab, Oxford OX1 3PU, England
[3] Natl Univ Singapore, Ctr Quantum Technol, Singapore 117543, Singapore
[4] Politecn Milan, Dipartimento Fis, CNR, IFN, I-20133 Milan, Italy
[5] Univ Tokyo, Dept Adv Mat Sci, Chiba 2778561, Japan
[6] Natl Inst Adv Ind Sci & Technol, Tsukuba, Ibaraki 3058562, Japan
[7] Max Planck Inst Solid State Res, D-70569 Stuttgart, Germany
[8] Univ Stuttgart, Phys Inst 4, D-70550 Stuttgart, Germany
[9] Univ Bath, Dept Phys, Bath BA2 7AY, Avon, England