= Vacuum state
{title2=$|0\rangle$}
= Quantum vacuum
{synonym}
For a stable relativistic <quantum field theory> in Minkowski space, a vacuum is a lowest-energy state for the chosen time evolution; a physical vacuum is normally also invariant under spacetime translations. It need not have zero fluctuations or vanish under every field operator. A free field's <Fock vacuum> is annihilated by its <annihilation operators>, while an interacting vacuum need not equal the free-theory Fock state. Multiple degenerate vacua permit <spontaneous symmetry breaking>. In curved spacetime the choice of time evolution and positive-frequency modes introduces additional <vacuum ambiguity in a nonstationary spacetime>.
Back to article page
