On Wheeler's delayed-choice Gedankenexperiment and its laboratory realization

Abstract

We present an analysis and interpretation of the experiment performed by Jacques et al (2007 Science 315 966), which represents a realization of Wheeler's delayed-choice Gedankenexperiment. Our analysis is based on the evolution of the photon state, since the photon enters into the Mach-Zehnder interferometer (MZI) with a removable beam splitter until it exits. Given the same photon state incident on the output beam splitter BS(output), the photon's state at the exit will be very different depending on whether BSoutput is on or off. Hence, the statistics of photon counts collected by the two detectors, positioned along orthogonal directions at the exit of the interferometer, will also be very different for each case. Therefore, it is not that the choice of inserting (on) or removing (off) a beam splitter leads to a delayed influence on the photon behavior before arriving there, but that such a choice influences the photon state at and after BSoutput, i.e. after it has exited the MZI. The random on/off choice at BSoutput has no delayed effect on the photon to behave as a wave or a corpuscle at the entrance and inside the interferometer, but influences the subsequent evolution of the photon state incident on BS(output).