Recycling qubits for the generation of Bell nonlocality between independent sequential observers

Abstract

There is currently much interest in the recycling of entangled systems, for use in quantum information protocols by sequential observers. In this work, we study the sequential generation of Bell nonlocality via recycling one or both components of two-qubit states. We first give a description of two-valued qubit measurements in terms of measurement bias, strength, and reversibility, and derive useful tradeoff relations between them. Then, we derive one-sided monogamy relations for unbiased observables, that strengthen the recent Conjecture in [S. Cheng {\it et al.}, Phys. Rev. A \textbf{104}, L060201 (2021) ] that if the first pair of observers violate Bell nonlocality then a subsequent independent pair cannot, and give semi-analytic results for the best possible monogamy relation. We also extend the construction in [P. J. Brown and R. Colbeck, Phys. Rev. Lett. \textbf{125}, 090401 (2020)] to obtain (i)~a broader class of two-qubit states that allow the recycling of one qubit by a given number of observers on one side, and (ii)~a scheme for generating Bell nonlocality between arbitrarily many independent observers on each side, via the two-sided recycling of multiqubit states. Our results are based on a formalism that is applicable to more general problems in recycling entanglement, and hence is expected to aid progress in this field.

Minor corrections, More references, and revision of Fig. 2

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Cited by in corpus (19)

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• Device-independent self-testing of unsharp measurements
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• Sharing preparation contextuality in Bell experiment by arbitrary pair of sequential observers
• Resource theoretic efficacy of the single copy of a two-qubit entangled state in a sequential network
• Secure and robust randomness with sequential quantum measurements
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• Sequentially witnessing entanglement by independent observer pairs
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• Recycled detection of genuine multiparty entanglement of unlimitedly stretched array of parties and arbitrarily long series of sequential observers
• Sharing nonlocality in a network using the quantum violation of chain network inequality
• Mermin and Svetlichny inequalities for non-projective measurement observables
• Sequential information theoretic protocols in continuous variable systems