in the delayed-choice quantum eraser, entangled photon pairs are created via spontaneous parametric down-conversion in a crystal, with the signal photon passing through a double-slit to potentially form an interference pattern. which-path info is encoded by polarizing or routing the idler photon based on the signal's slit choice, marking the path via entanglement—destroying wave behavior until erased. erasure occurs post-detection by mixing idler paths with a beam splitter, scrambling the info so correlated subsets on the signal detector restore interference without retroactive time travel. wikipedia.

Delayed-choice quantum eraser - Wikipedia