1. Centre for Quantum Technologies, National University of Singapore, Singapore 117543, Singapore
2. Atomic and Laser Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
3. Photon Science Institute and School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
4. Centre for Quantum Dynamics, Imperial College London, London SW7 2AZ, United Kingdom