Steven Chu ( Chinese : 朱棣文 ; pinyin : Zhū Dìwén , born February 28 , 1948 ) is an American physicist who served as the 12th United States Secretary of Energy from 2009 to 2013 .
Steven Chu ( born February 28 , 1948 ) is an American physicist who served as the 12th United States Secretary of Energy from 2009 to 2013 .