In
quantum mechanics, the
interaction picture (also known as the
Dirac picture) is an intermediate representation between the
Schrödinger picture and the
Heisenberg picture. Whereas in the other two pictures either the
state vector or the
operators carry time dependence, in the interaction picture both carry part of the time dependence of
observables. The interaction picture is useful in dealing with changes to the wave functions and observable due to interactions. Most field theoretical calculations use the interaction representation because they construct the solution to the many body Schrödinger equation as the solution to the free particle problem plus some unknown interaction parts.