1. QTF Centre of Excellence, Turku Centre for Quantum Physics, Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland
2. QTF Centre of Excellence, Department of Physics, University of Helsinki, P.O. Box 43, 00014 Helsinki, Finland
3. Department of Physics, Nanoscience Center, University of Jyväskylä, 40014 Jyväskylä, Finland
4. Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy
5. INFN, Sezione di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy