Chiral Asymmetry: The Quantum Physics of Handedness

Abstract

Molecules (such as glucose) or configurations of molecules (such as silicon dioxide in quartz) that do not superpose on their mirror image are chiral structures. They interact differently with left and right circularly polarized light, giving rise to a class of phenomena termed optical activity. A quantum electrodynamic analysis of optical activity shows that the effects are due to the quantum interference of electric-dipole and magnetic-dipole transitions between the same states. For such transitions to occur simultaneously, the states involved must not be parity eigenstates. Achiral matter in rotation is also predicted to display optical activity, and the author discusses the possibility of observing the influence of the Earth’s rotation on atomic spectra. He also describes the successful observation of optical activity in the specular reflection of light from a naturally chiral medium. Since chiral matter interacts differently with the two forms of circularly polarized light, one may likewise expect it to scatter orthogonal states of spin-polarized electrons differently, an expectation confirmed by experiment.