Bose condensation,solitons and canonical transformations in quantum field theory

In an quantum sine-Gordon model in 1+1 dimensions, the condition that the vacuum expectation value of the Heisenberg scalar field reproduces static soliton solution to the classical equation is satisfied when the LSZ asymptotic quantum field undergoes a canonical transformation. This can be viewed as a quantum image of the Bäcklund transformation and the soliton is described in terms of condensation of quanta. Their confinement is ascribed to the non-implementability of unitary transformations among unitary inequivalent representations of the canonical commutation relations.Invited talk at the International Symposium Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 14–21, 1981.It is a pleasure to thank Professor J. Niederle and the Organizing Committee for the opportunity of participating in this Symposium and for the kind hospitality.