  For the study of quantum dynamics the use of Wigner's phase space
representation can be rewarding. It describes the state by Wigner's real-valued
distribution W and its dynamics by a vector field in phase space, the Wigner
current J . Basically, only the Wigner representation can be used for this type
of visual study of quantum dynamics so conveniently and directly. What does it
teach us about the most fundamental ingredient of quantum dynamics, the quantum
jump between energy levels? Quite a lot, as it turns out.
