Among the different branches of quantum mechanics, quantum electrodynamics (QED) has undergone the most extensive experimental testing and validation. QED describes the behavior of electromagnetic interactions, including the interaction of light (photons) with charged particles (such as electrons and positrons).
QED has been subjected to numerous experimental tests over the years, and its predictions have been verified with remarkable precision. For example, the anomalous magnetic moment of the electron, which is a measure of its magnetic properties, has been measured to an extremely high degree of accuracy and agrees with QED calculations to several decimal places. Similarly, the Lamb shift, which is the splitting of energy levels in the hydrogen atom, has been measured and confirmed in experiments, validating QED predictions.
The development and success of QED were greatly influenced by the work of Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga, who were jointly awarded the Nobel Prize in Physics in 1965 for their contributions to the theory of quantum electrodynamics.
Other branches of quantum mechanics, such as quantum chromodynamics (QCD) which describes the strong interaction between quarks and gluons, have also been extensively tested through experimental measurements. However, the precision and success of experimental tests in QED are particularly notable, making it one of the most well-confirmed branches of quantum mechanics.