Strict Hierarchy between Parallel, Sequential, and Indefinite-Causal-Order Strategies for Channel Discrimination

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...

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Bibliographic Details
Published in:Physical review letters 2021-11, Vol.127 (20), p.200504-200504, Article 200504
Main Authors: Bavaresco, Jessica, Murao, Mio, Quintino, Marco Túlio
Format: Article
Language:English
Subjects:
Channels
Discrimination
Qubits (quantum computing)
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Summary: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 strategies is not exclusive to our main example.
ISSN:0031-9007
1079-7114
DOI:10.1103/physrevlett.127.200504