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  • Open Access

Entropic witness for quantum memory in open system dynamics

Charlotte Bäcker1,*, Konstantin Beyer1,2,†, and Walter T. Strunz1,‡

  • *Contact author: charlotte.baecker@tu-dresden.de
  • †Contact author: kbeyer1@stevens.edu
  • ‡Contact author: walter.strunz@tu-dresden.de
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Phys. Rev. Research 7, 033256 – Published 15 September, 2025

DOI: https://doi.org/10.1103/618n-fp8w

Abstract

The dynamics of open quantum systems are often modeled by non-Markovian processes that account for memory effects arising from interactions with the environment. It is well known that the memory provided by the environment can be classical or quantum in nature. Remarkably, the quantumness of the memory can be witnessed locally by measurements on the open system alone, without requiring access to the environment. However, existing witnesses are computationally challenging for systems beyond qubits, which severely limits their practical applicability. In this work, we present a tractable criterion for quantum memory based on the von Neumann entropy, which is easily computable for systems of any dimension. Using this witness, we investigate the nature of memory in a class of physically motivated finite-dimensional qudit dynamics. Moreover, we demonstrate that this criterion is also suitable for detecting quantum memory in continuous-variable systems. As an illustrative example, we analyze non-Markovian Gaussian dynamics of a damped harmonic oscillator.

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Phys. Rev. Research 7, 033256– Published 15 September, 2025
  • Received 5 February 2025
  • Accepted 21 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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