We report a new insight into the understanding of duality in physics. We have found that the long-known inequality that links visibility and which-path distinguishability can be completed into an equality. We will show that accounting for vector space entanglement, as previously overlooked, serves as a missing link, and provides fresh insight into wave-particle complementarity and duality.

Professor Eberly received his BS in Physics from Penn State (1957) and his PhD in Physics from Stanford University (1962). He joined the UR Physics and Astronomy faculty in 1967, where he is a member of the Quantum Optics research group. Since 1979 he has held an adjunct faculty position in the Institute of Optics. He is presently the Andrew Carnegie Professor of Physics and Director of the Rochester Theory Center. Professor Eberly is a Fellow of the American Physical Society and the Optical Society of America, has been Chair of the APS Division of Laser Science and president of the Optical Society of America in 2007. Professor Eberly is recognized as an icon in the field of theoretical quantum optics, and has been the recipient of the Charles Hard Townes Award, the Smoluchowski Medal and the Senior Humboldt Award. For his outstanding contributions in the theory of electron localization in atoms and molecules he was awarded in 2010 the Frederic Ives Medal, the highest award of the Optical Society of America.