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A fundamental problem that illustrates this statement is given by the task of channel discrimination, in which an unknown channel drawn from a known random ensemble should be determined by applying it for a single time. In this paper, we characterise the quality of channel discrimination protocols when the quantum memory, quantified by the auxiliary dimension, is limited. This is achieved by formulating the problem in terms of separable quantum states with additional affine constraints that all of their factors in each separable decomposition obey. We discuss the computation of upper and lower bounds to the solutions of such problems which allow for new insights into the role of memory in channel discrimination. In addition to the single-copy scenario, this methodological insight allows to systematically characterise quantum and classical memories in adaptive channel discrimination protocols. Especially, our methods enabled us to identify channel discrimination scenarios where classical or quantum memory is required, and to identify the hierarchical and non-hierarchical relationships within adaptive channel discrimination protocols.<\/jats:p>","DOI":"10.22331\/q-2026-01-28-1988","type":"journal-article","created":{"date-parts":[[2026,1,28]],"date-time":"2026-01-28T10:17:48Z","timestamp":1769595468000},"page":"1988","update-policy":"https:\/\/doi.org\/10.22331\/q-crossmark-policy-page","source":"Crossref","is-referenced-by-count":2,"title":["Characterising memory in quantum channel discrimination via constrained separability problems"],"prefix":"10.22331","volume":"10","author":[{"given":"Ties-Albrecht","family":"Ohst","sequence":"first","affiliation":[{"name":"Naturwissenschaftlich-Technische Fakult\u00e4t, Universit\u00e4t Siegen, Siegen 57068, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shijun","family":"Zhang","sequence":"additional","affiliation":[{"name":"Sorbonne Universit\u00e9, CNRS, LIP6, F-75005 Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hai Chau","family":"Nguyen","sequence":"additional","affiliation":[{"name":"Naturwissenschaftlich-Technische Fakult\u00e4t, Universit\u00e4t Siegen, Siegen 57068, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Martin","family":"Pl\u00e1vala","sequence":"additional","affiliation":[{"name":"Naturwissenschaftlich-Technische Fakult\u00e4t, Universit\u00e4t Siegen, Siegen 57068, Germany"},{"name":"Institut f\u00fcr Theoretische Physik, Leibniz Universit\u00e4t Hannover, Hannover, Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marco T\u00falio","family":"Quintino","sequence":"additional","affiliation":[{"name":"Sorbonne Universit\u00e9, CNRS, LIP6, F-75005 Paris, France"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"9598","published-online":{"date-parts":[[2026,1,28]]},"reference":[{"key":"0","doi-asserted-by":"publisher","unstructured":"N. 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