Entanglement and photoelectron holography in dissociative photoionization: molecular quantum eraser
In a double-slit experiment with a bipartite system, the visibility of interference fringes depends on the availability of which-way information. Here, we report the formation of a Bell-like state of photoelectron and residual ion in the multiphoton dissociative ionization of the D$_2$ molecule. Evidence for entanglement is provided by the correlated emission directions of photoelectron and ion, which is observed using a COLTRIMS reaction microscope. In the presence of this correlation, the holographic interference fringes contained in the photoelectron momentum distributions are suppressed, indicating the existence of which-way information. We show that the which-way information is erased, and the interference pattern is restored, when a single ionic state is selected. The experimental observations and conclusions are fully supported by the numerical solution of the electronic-nuclear time-dependent Schr\"odinger equation. Our work demonstrates that coincidence spectroscopy of ions and electrons is a powerful method for studying fundamental concepts of quantum information science within the context of ultrafast light-matter interactions.