In 1945, Rabi delivered the Richtmyer Memorial Lecture, held by the American Association of Physics Teachers in honor of Floyd K. Richtmyer, wherein he proposed that the magnetic resonance of atoms might be used as the basis of a clock. William L. Laurence wrote it up for The New York Times, under the headline "Cosmic pendulum for clock planned". Before long Zacharias and Ramsey had built such atomic clocks. Rabi actively pursued his research into magnetic resonance until about 1960, but he continued to make appearances at conferences and seminars until his death.
Rabi chaired Columbias physics department from 1945 to 1949, during which time it was home to two Nobel laureates (Rabi and Enrico Fermi) and eleven future laureates, including seven faculty (Polykarp Kusch, Willis Lamb, Maria Goeppert-Mayer, James Rainwater, Norman Ramsey, Charles Townes and Hideki Yukawa), a research scientist (Aage Bohr), a visiting professor (Hans Bethe), a doctoral student (Leon Lederman) and an undergraduate (Leon Cooper). Martin L. Perl, a doctoral student of Rabis, won the Nobel Prize in 1995. Rabi was the Eugene Higgins professor of physics at Columbia but when Columbia created the rank of university professor in 1964, Rabi was the first to receive such a chair. This meant that he was free to research or teach whatever he chose. He retired from teaching in 1967 but remained active in the department and held the title of University Professor Emeritus until his death. A special chair was named after him in 1985.
A legacy of the Manhattan Project was the network of national laboratories, but none was located on the East Coast. Rabi and Ramsey assembled a group of universities in the New York area to lobby for their own national laboratory. When Zacharias, who was now at MIT, heard about it, he set up a rival group at MIT and Harvard. Rabi had discussions with Major General Leslie R. Groves Jr., the director of the Manhattan Project, who was willing to go along with a new national laboratory, but only one. Moreover, while the Manhattan Project still had funds, the wartime organization was expected to be phased out when a new authority came into existence. After some bargaining and lobbying by Rabi and others, the two groups came together in January 1946. Eventually nine universities (Columbia, Cornell, Harvard, Johns Hopkins, MIT, Princeton, Pennsylvania, Rochester and Yale) came together, and on January 31, 1947, a contract was signed with the Atomic Energy Commission (AEC), which had replaced the Manhattan Project, that established the Brookhaven National Laboratory.
Rabi suggested to Edoardo Amaldi that Brookhaven might be a model that Europeans could emulate. Rabi saw science as a way of inspiring and uniting a Europe that was still recovering from the war. An opportunity came in 1950 when he was named the United States Delegate to the United Nations Educational, Scientific and Cultural Organization (UNESCO). At a UNESCO meeting at the Palazzo Vecchio in Florence in June 1950, he called for the establishment of regional laboratories. These efforts bore fruit; in 1952, representatives of eleven countries came together to create the Conseil Européen pour la Recherche Nucléaire (CERN). Rabi received a letter from Bohr, Heisenberg, Amaldi and others congratulating him on the success of his efforts. He had the letter framed and hung it on the wall of his home office.