A Review of the ZWM Study; What Destroys the Interference?
Thomas Alexander Meyer · 2013
In 1991-1992 three papers were published by the same authors referred to as the ZWM study 1,2,3 concerning the subject of induced coherence in photon downconversion. We present a review of these papers which all concern the same experimental arrangement. The central conclusion made by the authors is that interference is destroyed by the in principle knowability of path, that path indistinguishability is fundamental to interference effects. We review these papers with an emphasis on validating this conclusion and attempting to understand the action that is taken in the preparation of the “idler ” photon and the subsequent affect that this action has on the interference visibility of the entangled “signal ” photon. The ZWM Paper The first paper published in this study, reference 1, is an experimental paper which takes its naming from the ordering of the authors; Zou, Wang and Mandel. This paper presents an experiment with induced coherence between the outputs of two separate photon downconversions, typically referred to as signal and idler photons, which is demonstrated by the presence of single photon interference between the two possible sources of signal photon. The experimental setup is illustrated in Figure 1 where a pump wave is beam split (BSp) into two coherent pump beams that are made incident upon the