  Zitterbewegung of a Dirac electron is an oscillation between positive and
negative energy states, and is thus distinct from the analogous phenomena
exhibited by spin half charged particles in electric and magnetic fields.
Quantum field theory offers an insight into the velocity operator and provides
an interpretation of zitterbewegung. Applying stationary perturbation theory to
these results the electron $g$ factor is obtained analytically up to the
Schwinger correction ($g = 2 + \alpha/\pi $).
