Delayed-Choice Test of Quantum Complementarity with Interfering Single Photons

Abstract

We report an experimental test of quantum complementarity with single-photon pulses sent into a Mach-Zehnder interferometer with an output beam splitter of adjustable reflection coefficient $R$. In addition, the experiment is realized in Wheeler’s delayed-choice regime. Each randomly set value of $R$ allows us to observe interference with visibility $V$ and to obtain incomplete which-path information characterized by the distinguishability parameter $D$. Measured values of $V$ and $D$ are found to fulfill the complementarity relation $V^2+D^2\le 1$.