We study the ground state energy and ground states of systems coupling
nonrelativistic quantum particles and force-carrying Bose fields, such as radiation, in
the quasiclassical approximation. The latter is very useful whenever the
force-carrying field has a very large number of excitations and thus behaves in a
semiclassical way, while the nonrelativistic particles, on the other hand, retain their
microscopic features. We prove that the ground state energy of the fully microscopic
model converges to that of a nonlinear quasiclassical functional depending on both
the particles’ wave function and the classical configuration of the field. Equivalently,
this energy can be interpreted as the lowest energy of a Pekar-like functional with an
effective nonlinear interaction for the particles only. If the particles are confined, the
ground state of the microscopic system converges as well, to a probability
measure concentrated on the set of minimizers of the quasiclassical energy.
Keywords
quasiclassical limit, interaction of matter and light,
semiclassical analysis