In 1945 he developed an approximation method for many-body physics. As Sidney Dancoff developed it independently in 1950, it is now called the Tamm-Dancoff approximation.
In 1951 together with Andrei Dmitrievich Sakharov proposed a tokamak system of the realization of CTF on the basis of toroidal magnetic thermonuclear reactor and soon after the first such devices were built by the INF, resulting the T-3 Soviet magnetic confinement device from 1968, when the plasma parameters unique for that time were obtained, of showing the temperatures in their machine to be over an order of magnitude higher than what was expected by the rest of the community. The western scientists visited the experiment and verified the high temperatures and confinement, sparking a wave of optimism for the prospects of the tokamak as well as construction of new experiments, which is still the dominant magnetic confinement device today.
Tamm was a student of Leonid Isaakovich Mandelshtam in science and life.