Canonical State Renormalisation in Photo-Excitation
P. D. Drummond · Physica Scripta · 1988
Theories of the interactions of charged particles and the electromagnetic vacuum are reviewed. A new technique is introduced in which a canonical transformation is used to transform the Hamiltonian to one without counter-rotating terms. In the new Hamiltonian, the dressed ground-state coincides with the ground-state of the free Hamiltonian. A feature of the Hamiltonian is that it can be regarded as having a symmetric combination of momentum ( p.A ) and position ( d.E ) couplings. The new theory is able to treat transitions occurring on time-scales of an optical period or less. The coupling varies as f 1/2 at low frequencies, and so the theory does not have the infra-red divergence or causality problems that occur in minimal coupling theories.