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  • Open Access

Simulating Quantum Instruments with Projective Measurements and Quantum Postprocessing

Shishir Khandelwal and Armin Tavakoli

  • Physics Department and NanoLund, Lund University, Box 118, 22100 Lund, Sweden

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Phys. Rev. Lett. 135, 040202 – Published 23 July, 2025

DOI: https://doi.org/10.1103/bhr5-g71p

Abstract

Quantum instruments describe both the classical outcome and the updated state associated with a quantum measurement. We ask whether these processes can be simulated using only a natural subset of resources, namely projective measurements on the system and quantum processing of the postmeasurement states. We show that the simulability of instruments can be connected to an entanglement classification problem. This leads to a computationally efficient necessary condition for simulation of generic instruments and to a complete characterisation for qubits. We use this to address relevant quantum information tasks, namely (i) the noise tolerance of standard qubit unsharp measurements, (ii) nonprojective advantages in information-disturbance trade-offs, and (iii) increased sequential Bell inequality violations under projective measurements. Moreover, we consider also d-dimensional Lüders instruments that correspond to weak versions of standard basis measurements and show that for large d these can permit scalable noise advantages over projective implementations.

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Outline

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Phys. Rev. Lett. 135, 040202– Published 23 July, 2025
  • Received 2 March 2025
  • Revised 4 June 2025
  • Accepted 30 June 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. Funded by Bibsam.

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