1. Institute for Quantum Science and Technology, University of Calgary, Calgary, Alberta T2N 1N3, Canada
2. National Institute for Nanotechnology, 11421 Saskatchewan Dr. NW, Edmonton, Alberta T6G 2M9, Canada
3. Department of Physics, City College of New York, New York, New York 10031, USA
4. Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, 13083-970 Campinas, São Paulo, Brazil