We replace the usual heuristic notion of quantum cell by that of 'quantum blob', which does not depend on the dimension of phase space. Quantum blobs, which are defined in terms of symplectic capacities, are canonical invariants. They allow us to prove an exact uncertainty principle for semiclassically quantized Hamiltonian systems. (C) 2003 Elsevier B.V. All rights reserved.
symplektisk topologi