We propose and realize a variation of Mandel's experiment where the Englert's inequality can be demonstrated. This is a relation of the coherence and the which-way information, which is one of the most fundamental results of the quantum physics. The main problem of the experiments relating coherence and which-way information is the fact that the which-way information is difficult to measure directly from the laboratory. What we measure at the laboratory are the first and second-order normalized correlation functions, which are well defined and are easy to obtain because they are directly related to the number of photons detected by the detectors. We obtain the visibility (which is a measure of the coherence) from the first-order normalized correlation function. The innovation in our experiment is that we obtain the distinguishability (which is a measure of the which-way information) as a function of the second-order normalized correlation functions. Once they are obtained, we demonstrate that the Englert's inequality is held.

Demostramos una nueva manera de medir el principio de complementariedad de Bohr mediante la medida de funciones de correlación de primer y segundo orden.

Demostrem una nova manera de mesurar el principi de complementarietat de Bohr mitjançant la mesura de funcions de correlació de primer i segon ordre.