1. Department of Physics 1 , William & Mary, Williamsburg, Virginia 23187, USA
2. JILA, National Institute of Standards and Technology and the University of Colorado 2 , Boulder, Colorado 80309, USA
3. Department of Physics, University of Colorado 3 , Boulder, Colorado 80309, USA
4. Department of Physics, Kennesaw State University 4 , Marietta, Georgia 30060, USA
5. Department of Physics, The University of Texas at Dallas 5 , Richardson, Texas 75080, USA