Two years later, he returned to Japan due to the outbreak of the Second World War, but finished his doctoral degree (Dissertation PhD from University of Tokyo) on the study of nuclear materials with his thesis on work he had done while in Leipzig.

In 1948, he and his students re-examined a 1939 paper by Sidney Dancoff that attempted, but failed, to show that the infinite quantities that arise in quantum electrodynamics (QED) can be canceled with each other.

With this term, the theory gave finite results; thus Tomonaga discovered the renormalization method independently of Julian Schwinger and calculated physical quantities such as the Lamb shift at the same time.

[4] In 1965, he was awarded the Nobel Prize in Physics, with Julian Schwinger and Richard P. Feynman, for the study of QED, specifically for the discovery of the renormalization method.

In recognition of three Nobel laureates' contributions, the bronze statues of Shin'ichirō Tomonaga, Leo Esaki, and Makoto Kobayashi was set up in the Central Park of Azuma 2 in Tsukuba City in 2015.