A wave-particle delayed-choice experiment with a single-photon state

We perform a new wave-particle delayed-choice experiment which uses photon pairs produced by parametric fluorescence. One of the photons of a pair serves as a trigger photon, the other one traverses a Mach-Zehnder ring interferometer. The trigger photon switches the interferometer between registration of either pathway information or phase information for the second photon. The result turns out to be independent of whether the switching process takes place before or after the photon passes the first beamsplitter of the interferometer.