The stability of the QED vacuum in the temporal gauge

The stability of the vacuum for QED in the temporal gauge will be examined. It is generally assumed that the vacuum state is the quantum state with the lowest energy. However, it is easy to show that this is not true in general but depends on the nature of the Hamiltonian that describes the system. It will be shown that this assumption does not hold for a system consisting of a fermion field coupled to a quantized electromagnetic field in the temporal gauge.