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Closed timelike curves are striking predictions of general relativityallowing for time-travel. They are afflicted by notorious causality issues(e.g. grandfather's paradox). Quantum models where a qubit travels back in timesolve these problems, at the cost of violating quantum theory's linearity -leading e.g. to universal quantum cloning. Interestingly, linearity is violatedeven by open timelike curves (OTCs), where the qubit does not interact with itspast copy, but is initially entangled with another qubit. Non-linear dynamicsis needed to avoid violating entanglement monogamy. Here we propose analternative approach to OTCs, allowing for monogamy violations. Specifically,we describe the qubit in the OTC via a pseudo-density operator - a unifieddescriptor of both temporal and spatial correlations. We also simulate themonogamy violation with polarization-entangled photons, providing apseudo-density operator quantum tomography. Remarkably, our proposal applies toany space-time correlations violating entanglement monogamy, such as thosearising in black holes.

Theoretical description and experimental simulation of quantum entanglement near open time-like curves via pseudo-density operators