It has been suggested that this article or section be merged with Dyson operator. (Discuss)

In quantum mechanics, suppose we have a Hamiltonian H which for some reason or other, we split into a "free" part H₀ and an "interacting" part H_int i.e. H=H₀+H_int. We will work in the interaction picture here. Wikipedia does not have an article with this exact name. ... It has been suggested that this article or section be merged with Dyson series. ... Fig. ... In physics, Hamiltonian has distinct but closely related meanings. ... In quantum mechanics, the Interaction picture (or Dirac picture) is an intermediate between the Schrödinger picture and the Heisenberg picture. ...

Then, for t>t₀,

where is the time-ordering operator. In theoretical physics, path-ordering is the procedure (or a meta-operator ) of ordering a product of many operators according to the value of one chosen parameter: Here is a permutation that orders the parameters: Examples If an operator is not simply expressed as a product, but as a function...

This is a perturbative series which typically diverges asymptotically. This is called the Dyson series. In quantum mechanics, perturbation theory is a set of approximation schemes for describing a complicated quantum system in terms of a simpler one. ... In mathematics and applications, particularly the analysis of algorithms, asymptotic analysis is a method of classifying limiting behaviour, by concentrating on some trend. ...

Returning to the Schrödinger picture, for t_f > t_i, In quantum mechanics, a state function is a linear combination (a superposition) of eigenstates (the exception is if a state function is itself an eigenstate). ...

This is the old-fashioned way of deriving the Feynman diagrams. A Feynman diagram is a bookkeeping device for performing calculations in quantum field theory, invented by American physicist Richard Feynman. ...