Thomas Young’s slit experiment lies at the heart of classical interference and quantum mechanics. Over the last 50 years, it has been shown that particles (e.g., photons, electrons, large molecules), even individual particles, generate an interference pattern at a distant screen after passage through a double slit, thereby demonstrating wave-particle duality. We revisit this famous experiment by replacing both slits with single-mode fiber inputs to two independent quantum memories that are capable of storing the incident electromagnetic field’s amplitude and phase as a function of time. At a later time, the action is reversed: the quantum memories are read out in synchrony, and the single-mode fiber outputs are allowed to interact, consistent with the original observation. In contrast to any classical memory device, the write and read processes of a quantum memory are non-destructive and hence preserve the photonic quantum states. In principle, with sufficiently long storage times and sufficiently high photonic storage capacity, quantum memories operating at widely separated telescopes can be brought together to achieve optical interferometry over arbitrarily long baselines. (C) 2021 Optical Society of America