satisfied by the field in the (source free) vacuum. For this reason is often referred to as the "vacuum field", although it is of course a Heisenberg-picture operator acting on whatever state of the field happens to be appropriate at . is the source field, the field generated by the dipole and acting on the dipole.
satisfied by the field in the (source free) vacuum For this reason is often referred to as the "vacuum field", although it is of course a Heisenberg-picture operator acting on whate.ver state of the field happens to be appropriate at . is the source field, the field generated by the dipole and acting on the dipole.