Definition of "quantum mechanics" []

• Quantum theory, especially the quantum theory of the structure and behavior of atoms and molecules. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The test confirmed an under­lying theory of quantum mechanics — namely, that a measurement made on one photon has an instantaneous ef­fect on the nature of another photon."
• "When I was a graduate student in physical chemistry at Yale, I had the remarkable experience of taking a course in relativistic quantum mechanics from Nobel laureate Willis Lamb."
• "My intellectual life was immersed in quantum mechanics and second-order differential equations, and my heroes were the giants of physics—Albert Einstein, Niels Bohr, Werner Heisenberg, and Paul Dirac."