The Principle of Stationary Variance in Quantum Field Theory

The principle of stationary variance is advocated as a viable variational approach to quantum field theory. The method is based on the principle that the variance of energy should be at its minimum when the state of a quantum system reaches its best approximation for an eigenstate. While not too much popular in quantum mechanics, the method is shown to be valuable in quantum field theory, and three special examples are given in very different areas ranging from Heisenberg model of antiferromagnetism to quantum electrodynamics and gauge theories.