1. NTT Secure Platform Laboratories, NTT Corporation, Musashino, Tokyo 180-8585, Japan
2. Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom
3. Center on Frontiers of Computing Studies, Department of Computer Science, Peking University, Beijing 100871, China
4. Stanford Institute for Theoretical Physics, Stanford University, Stanford, CA 94305, U.S.A.