1. ICFO−Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain
2. Centre
for Engineered Quantum Systems, Centre for Quantum Computation and
Communication Technology, and School of Mathematics and Physics, The University of Queensland, Brisbane QLD 4072, Australia
3. Department
of Signal Theory and Communications, Campus Nord D3, Universitat Politecnica de Catalunya, 08034 Barcelona, Spain