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  • Open Access

Separation between entanglement criteria and entanglement detection protocols

Zhenhuan Liu1,*,† and Fuchuan Wei2,*,‡

  • 1Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing 100084, China
  • 2Yau Mathematical Sciences Center and Department of Mathematics, Tsinghua University, Beijing 100084, China

  • *These authors contributed equally to this work.
  • †Contact author: qubithuan@gmail.com
  • ‡Contact author: wfc21@mails.tsinghua.edu.cn
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Phys. Rev. Research 7, 033121 – Published 5 August, 2025

DOI: https://doi.org/10.1103/hm8j-wgqm

Abstract

Entanglement detection is one of the most fundamental tasks in quantum information science, playing vital roles in theoretical studies and quantum system benchmarking. Researchers have proposed many powerful entanglement criteria with high detection capabilities and small observable numbers. Nonetheless, entanglement criteria only represent mathematical rules deciding the existence of entanglement. The relationship between a good entanglement criterion and an effective experimental entanglement detection protocol (EDP) is poorly understood. In this study, we introduce postulates for EDPs about their detection capabilities and robustness and use them to show the difference between entanglement criteria and EDPs. Specifically, we design an entanglement detection task for unknown pure bipartite states and demonstrate that the sample complexity of any EDP and the number of observables for a good entanglement criterion can have exponential separation. Furthermore, we discover that the optimal EDP with the lowest sample complexity does not necessarily correspond to an entanglement criterion constructed by a small number of observables. Our results can be used to prove the exponential speedups achieved through quantum memory and be generalized to multipartite entanglement detection. By highlighting the significance and independence of EDP design, our work holds practical implications for entanglement detection experiments.

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Phys. Rev. Research 7, 033121– Published 5 August, 2025
  • Received 19 March 2024
  • Accepted 23 July 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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