1. Department of Physics, MIT-Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, Massachusetts Institute of Technology (MIT), Cambridge, MA 02139, USA.
2. Department of Physics and Astronomy, San José State University, San José, CA 95192, USA.
3. Department of Physics, The Ohio State University, Columbus, OH 43210, USA.
4. Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68.528, 21941-972 Rio de Janeiro, RJ, Brazil.
5. Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA.