1. Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA.
2. Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, CA 91125, USA.
3. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
4. Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA.
5. Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, USA.