However, in 1951 Edward Teller and mathematician Stanislaw Ulam came up with a workable design for a hydrogen bomb – now known as the Teller-Ulam design. The program of 1951, on the other hand, was technically so attractive that you could not argue with it. President until early 2015 was Giorgio Napolitano, also from the left: he belonged to the party Democratici di Sinistra. Strauss and Senator Brien McMahon, author of the Atomic Energy Act of 1946, urged President Eisenhower to revoke Oppenheimer's security status. Following the creation of the Atomic Energy Commission—a non-military agency overseeing nuclear research and nuclear weapons development—in 1946, Oppenheimer was immediately appointed head of the AEC's scientific advisory committee and left the Los Alamos Directorate. In 1957, Oppenheimer bought a piece of land and beach on Saint John in the US Virgin Islands and lived there with his family. He was brought in as a direct replacement for John Arne Riise who had left for AS Roma. Given the lack of a workable design for such a weapon at the time, Oppenheimer felt that more could be achieved by building up a substantial arsenal of fission weapons.
The first hydrogen bomb, called "Ivy Mike", was tested in 1952 with an energy yield of 10.4 megatons of TNT equivalent – over 650 times the power of the weapons developed by Oppenheimer during World War II. The public interrogation that followed revolved entirely around Oppenheimer's past, his communist sympathies, and his association during the Manhattan Project with scientists suspected of treason or who were communists, including Klaus Fuchs. When the US government considered a rush program to develop a nuclear fusion bomb – a hydrogen bomb – Oppenheimer initially advised against it, although he had favored the development of such a weapon at the beginning of the Manhattan project. As head of the AEC's advisory committee, Oppenheimer lobbied vigorously for international arms control and more funding for basic science research. Oppenheimer refused and requested a public inquiry to establish his allegiance. Oppenheimer feared that if it were announced where such a demonstration would take place, the enemy would use American prisoners of war or other people there as human shields. Oppenheimer's brother Frank even had to appear before the House Un-American Activities Committee, where he admitted to having been a member of the Communist Party in the 1930s, but refused to name other people.
A year later, Frank Rijkaard also made the switch to Milan. Frank was subsequently relieved of his position at the university and became a cattle rancher in Colorado instead. He instead became director of the Institute for Advanced Study at Princeton, New Jersey. Oppenheimer's pride after the successful "Trinity" test faded and was replaced by disgust and guilt, though he never said he regretted building the weapon. It is unclear how much value the US government and military placed on the scientists' assessment of the weapon they had developed. Like many scientists of his generation, Oppenheimer believed that freedom from the threat of nuclear weapons could only be achieved through the influence of a transnational organization (for example, the newly formed United Nations). In 1953, Oppenheimer was considered a security risk and Eisenhower asked him to resign. But the contradictions in Oppenheimer's own testimony and his unpredictable behavior on the witness stand convinced some that he was untrustworthy and perhaps a security risk. During his interrogation, Oppenheimer made voluntary statements about the left-wing behavior of many of his scientific colleagues. Oppenheimer would later gain an important voice in the fierce social debates about the far-reaching consequences of this decision.
Nuclear physics became a model of power as the world's governments began to recognize the strategic and political importance of nuclear weapons and their dire consequences. Overnight, Oppenheimer became the national face of science and the symbol of a new kind of technocratic power. In his role as a political adviser, Oppenheimer made many enemies. The FBI was therefore prepared to provide Oppenheimer's political enemies with material to blacken him with. The Baruch Plan of 1946 called for the internationalization of nuclear power and was derived in part from Oppenheimer's op-eds. But to Oppenheimer's horror, the final plan contained a number of conditions that made it clear that the real goal was to stop the Soviet Union from developing its own nuclear weapons, not to establish a lasting mechanism for international nuclear arms control. Oppenheimer opposed the petition and warned Szilard and Teller not to oppose the project.