 After a brief period of postdoctoral work at the University of Washington, he joined the faculty of Stanford University in 1971, where (with Helen Quinn) he originated Peccei–Quinn theory, still the most famous proposed solution to the strong CP problem.In 1978, he returned to Europe as a staff member of the Max Planck Institute in Munich, Germany.He joined the "Deutsches Elektronen-Synchrotron" (DESY) Laboratory in Hamburg, Germany, as the Head of the Theoretical Group in 1984.