1. Center for Quantum Phenomena, Department of Physics, New York University, New York, New York 10003, United States
2. Department of Physics, William & Mary, Williamsburg, Virginia 23187, United States
3. Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
4. Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87123, United States