= Canonical quantization of the electromagnetic field
The <electromagnetic four-potential> has a vanishing temporal momentum and a <Gauss law constraint in gauge theory>. Gauge reduction leaves two transverse <canonical pairs>. Their <canonical commutation relations> give the <photon> creation and <annihilation operators>. Covariant <Gupta-Bleuler quantization> instead retains auxiliary polarization modes and selects the same physical state space by a subsidiary condition and null-state quotient.
Back to article page
