David P. DeMille is an American physicist and Bloomberg Distinguished Professor of atomic/molecular physics and precision measurement at Johns Hopkins University. He holds appointments in the Department of Physics and Astronomy in the Krieger School of Arts and Sciences and in the Research and Exploratory Development Department at the Applied Physics Laboratory. He is best known for his use of polar diatomic molecules to search for symmetry-violating effects within the molecules and as a means for manipulating the external properties of the molecules.