1. Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
2. Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YB, United Kingdom
3. Center for Computing Research, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA
4. Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21941-972 Rio de Janeiro, Brazil