transition amplitude
nounA number that tells how likely a quantum system is to change from one state to another.
The transition amplitude between the two energy levels was small, so the atom rarely jumped.
OTHER MEANINGS
2. In scattering theory, the complex number whose squared magnitude gives the probability of a particle scattering into a particular final state.
The scattering transition amplitude was computed to first order in perturbation theory.
3. A matrix element of the time-evolution operator between initial and final basis states.
We evaluated the transition amplitude using the time-evolution operator in the interaction picture.
4. In quantum field theory, the quantity obtained from a Feynman diagram that encodes the probability of a specified particle process.
Summing all diagrams gave the full transition amplitude for the decay.