Entanglement inference from quantum erasure and path discrimination

Abstract

Fringes recovered by conditioning on quantum-eraser outcomes do not, by themselves, establish entanglement. We determine the minimum entanglement compatible with recorded eraser data when the preparation may be mixed, distinguishing these data from independently determined optimal which-path distinguishabilities and additional joint measurement outcomes. For noisy Greenberger-Horne-Zeilinger (GHZ) preparations, explicit compatible states establish sharp entanglement-depth thresholds and show how parity information strengthens certification. A matching converse establishes the exact threshold for two complete Pauli-outcome distributions. For an ideal three-qubit eraser, we classify the additional marker measurement directions that certify genuine multipartite entanglement within a fixed eraser configuration and determine the separate minima of compatible concurrence and squared GHZ fidelity for specified tilted axes. For noisy three-qubit data, an exact semidefinite characterization and constructive converse determine biseparable compatibility at arbitrary fixed local measurement axes, with rational certificates bounding one example. These results establish what entanglement is required by the measurement record, rather than inferred from assumptions about the source.