Affiliation: | (1) Institute for Quantum Information, Caltech 107–81, Pasadena, CA 91125, USA;(2) Department of Computer Science, University of Bristol, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB, U.K;(3) Department for Mathematical Analysis, Mathematical Institute, Budapest University of Technology and Economics, Egry József utca 2, 1111 Budapest, Hungary;(4) Department of Mathematics, University of Bristol, University Walk, Bristol, BS8 1 TW, U.K |