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arXiv · 2011.08300

Strict hierarchy between parallel, sequential, and indefinite-causal-order strategies for channel discrimination

Jessica Bavaresco·Mio Murao·Marco Túlio Quintino
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Abstract

We present an instance of a task of minimum-error discrimination of two qubit-qubit quantum channels for which a sequential strategy outperforms any parallel strategy. We then establish two new classes of strategies for channel discrimination that involve indefinite causal order and show that there exists a strict hierarchy among the performance of all four strategies. Our proof technique employs a general method of computer-assisted proofs. We also provide a systematic method for finding pairs of channels that showcase this phenomenon, demonstrating that the hierarchy between the strategies is not exclusive to our main example.

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Jessica Bavaresco, Mio Murao, Marco Túlio Quintino. 2021-11-17. Strict hierarchy between parallel, sequential, and indefinite-causal-order strategies for channel discrimination. https://doi.org/10.1103/physrevlett.127.200504

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