1. Centre for Engineered Quantum Systems, School of Physics, University of Sydney, Sydney, NSW 2006, Australia
2. Department of Physics and Center for Theory of Quantum Matter, University of Colorado Boulder, Boulder, Colorado 80309, USA
3. Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
4. Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA