Entangled photons, nonlocality, and Bell inequalities in the undergraduate laboratory

摘要

We use polarization-entangled photon pairs to demonstrate quantum nonlocality in an experiment suitable for advanced undergraduates. The photons are produced by spontaneous parametric downconversion using a violet diode laser and two nonlinear crystals. The polarization state of the photons is tunable. Using an entangled state analogous to that described in the Einstein-Podolsky-Rosen paradox, we demonstrate strong polarization correlations of the entangled photons. Bell's idea of a hidden variable theory is presented by way of an example and compared to the quantum prediction. A test of the Clauser, Home, Shimony, and Holt version of the Bell inequality finds S =2.307+/-0.035, in clear contradiction of hidden variable theories. The experiments described can be performed in an afternoon. (C) 2002 American Association of Physics Teachers. [References: 37]