Experimental realization of Popper's Experiment: Violation of the Uncertainty Principle?

Yoon-Ho Kim, Yanhua Shih

Published 1999-05-11, updated 1999-10-19Version 2

An entangled pair of photons (1 and 2) are emitted to opposite directions. A narrow slit is placed in the path of photon 1 to provide precise knowledge of its position on the $y$ axis and this also determines the precise $y$ position of its twin, photon 2, due to quantum entanglement. Is photon 2 going to experience a greater uncertainty in momentum, i.e., a greater $\Delta p_{y}$, due to the precise knowledge of its position $y$? The experimental data shows $\Delta y\Delta p_{y}<\hbar $ for photon 2. Can this recent realization of the historical thought experiment of Karl Popper signal a violation of the uncertainty principle?