Passage: Ernest Jeffrey Moniz, GCIH (born December 22, 1944) is an American nuclear physicist and former  United States Secretary of Energy, serving under U.S. President Barack Obama from May 2013 to January 2017. In June 2017, Moniz became co-chairman and chief executive officer of the Nuclear Threat Initiative, a nonpartisan, nonprofit organization working to prevent catastrophic attacks with weapons of mass destruction and disruption—nuclear, biological, radiological and cyber. He served as the Associate Director for Science in the Office of Science and Technology Policy in the Executive Office of the President of the United States from 1995 to 1997 and was Under Secretary of Energy from 1997 to 2001 during the Clinton Administration.

Question: What is Ernest Jeffrey Moniz's occupation?
nuclear physicist