1. Department of Physics, Department of Chemistry, and JILA, University of Colorado, Boulder 80309, Colorado, United States
2. MOE Key Laboratory of Advanced Micro-Structured Materials, and School of Physics Science and Engineering, Tongji University, Shanghai 200092, China
3. Department of Physics, University of Washington, Seattle 98195, Washington, United States
4. Department of Physics, School of Natural Sciences, Ulsan National Institute of Science and Technology, Ulsan, South Korea
5. Department of Physics and Astronomy, Texas A&M University, College Station 77843, Texas, United States