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Unbounded entanglement-sustaining sequential local quantum state discrimination

Debarupa Saha1,*, Priya Ghosh1,†, Kornikar Sen1,2,‡, Chirag Srivastava3,4,§, and Ujjwal Sen1,∥

  • *Contact author: debarupa73@gmail.com
  • †Contact author: priyaghosh1155@gmail.com
  • ‡Contact author: skornika@ucm.es
  • §Contact author: chirag.srivastava@ug.edu.pl
  • ∥Contact author: ujjwal@hri.res.in
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Phys. Rev. A 114, 012419 – Published 7 July, 2026

DOI: https://doi.org/10.1103/sdgn-mr8d

Abstract

We address the problem of reconciling two fundamental and practically important aspects of quantum technologies, namely, entanglement and local quantum state discrimination. Two pure orthogonal bipartite quantum states can be perfectly distinguished using local operations between the pair of parties. However, the measurement involved completely destroys the entanglement, a crucial resource for quantum technologies, rendering the postmeasurement states nonresourceful for many subsequent quantum tasks. To avoid complete destruction of entanglement, we propose a protocol that allows an arbitrary number of pairs of parties to distinguish between any two orthogonal, entangled, two-qubit pure states using local quantum operations and classical communication, with a success probability greater than that of random guessing, while ensuring that at each step, the individual ensemble states retain a finite amount of entanglement. Our protocol employs the minimum-error state discrimination approach. For demonstrating the retention of entanglement in the ensemble states at each step, we use a specific entanglement measure as well as the concept of entanglement witnessing. For a large family of sets of the two states, the success probability of discrimination can be as close as required to unity while sustaining a finite amount of entanglement at each step of an arbitrarily large sequence of state discrimination.

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Phys. Rev. A 114, 012419– Published 7 July, 2026
  • Received 20 September 2025
  • Accepted 12 June 2026
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