Second quantization

He named the resulting theory quantum electrodynamics.

He also coined the name second quantization for the process of counting the changing number of quantum oscillations or particles per state.

Schrodinger's approach of tracking the changing quantum state of each particle became the first quantization.

There's another reason this second quantization is better at describing the interactions of light and matter.

See, Schrodinger's approach has no idea how to destroy a particle.

All it can do is move particles around via their evolving wave functions.

An electron and a positron can annihilate each other and create two photons.

And that can even happen the other way around.