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

Nature communications 10(1)
Marletto, C.Vedral, V., Virzì, S. Rebufello, E. Avella, A. Piacentini, F.Gramegna, M.Degiovanni, I.P.Genovese, M. Clarendon Laboratory, University of Oxford, Parks Road, Oxford, UK

Fondazione ISI, Torino, Italy

Centre for Quantum Technologies, National University of Singapore

Department of Physics, National University of Singapore

Istituto Nazionale di Ricerca Metrologica, Torino, Italy

Politecnico di Torino, Italy

Istituto Nazionale di Ricerca Metrologica, Torino, Italy

INFN – sezione di Torino, Torino, Italy
2019 Physics

Closed timelike curves are striking predictions of general relativity allowing for time-travel. They are afflicted by notorious causality issues (e.g. grandfather’s paradox). Quantum models where a qubit travels back in time solve these problems, at the cost of violating quantum theory’s linearity—leading e.g. to universal quantum cloning.

Interestingly, linearity is violated even by open timelike curves (OTCs), where the qubit does not interact with its past copy, but is initially entangled with another qubit. Non-linear dynamics is needed to avoid violating entanglement monogamy. Here we propose an alternative approach to OTCs, allowing for monogamy violations. Specifically, we describe the qubit in the OTC via a pseudo-density operator—a unified descriptor of both temporal and spatial correlations.

We also simulate the monogamy violation with polarization-entangled photons, providing a pseudo-density operator quantum tomography. Remarkably, our proposal applies to any space-time correlations violating entanglement monogamy, such as those arising in black holes.

The article was published in: Nature communications 10(1): 182.

Full article

This work was supported (in part) by the Fetzer Franklin Fund of the John E. Fetzer Memorial Trust.