 By this time the Barnard Fellowship had expired and Rabi and Helen were living off a $ 182 per month stipend from the Rockefeller Foundation . They left Hamburg for Leipzig , where he hoped to work with Heisenberg . In Leipzig , he found Robert Oppenheimer , a fellow New Yorker . It would be the start of a long friendship . However , Heisenberg departed for a tour of the United States in March 1929 , so Rabi and Oppenheimer decided to go to the ETH Zurich , where Pauli was now the professor of Physics . Rabi 's education in physics was enriched by the leaders in the field he met there , which included Paul Dirac , Walter Heitler , Fritz London , Francis Wheeler Loomis , John von Neumann , John Slater , Leó Szilárd and Eugene Wigner . 
