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<article article-type="research-article" dtd-version="1.3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:lang="en"><front><journal-meta><journal-id journal-id-type="publisher-id">najo</journal-id><journal-title-group><journal-title xml:lang="en">Nanosystems: Physics, Chemistry, Mathematics</journal-title><trans-title-group xml:lang="ru"><trans-title>Наносистемы: физика, химия, математика</trans-title></trans-title-group></journal-title-group><issn pub-type="ppub">2220-8054</issn><issn pub-type="epub">2305-7971</issn><publisher><publisher-name>Университет ИТМО</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.17586/2220-8054-2019-10-4-398-401</article-id><article-id custom-type="elpub" pub-id-type="custom">najo-511</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research Article</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="en"><subject>PHYSICS</subject></subj-group><subj-group subj-group-type="section-heading" xml:lang="ru"><subject>ФИЗИКА</subject></subj-group></article-categories><title-group><article-title>Analysis of the unambiguous state discrimination with unequal a priori probabilities</article-title><trans-title-group xml:lang="ru"><trans-title></trans-title></trans-title-group></title-group><contrib-group><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Gaidash</surname><given-names>A. A.</given-names></name></name-alternatives><bio xml:lang="en"><p>Kronverkskiy, 49, St. Petersburg, 197101</p></bio><email xlink:type="simple">andrewdgk@gmail.com</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Medvedeva</surname><given-names>S. S.</given-names></name></name-alternatives><bio xml:lang="en"><p>Kronverkskiy, 49, St. Petersburg, 197101</p></bio><email xlink:type="simple">mdvdv.svt@gmail.com</email><xref ref-type="aff" rid="aff-1"/></contrib><contrib contrib-type="author" corresp="yes"><name-alternatives><name name-style="western" xml:lang="en"><surname>Miroshnichenko</surname><given-names>G. P.</given-names></name></name-alternatives><bio xml:lang="en"><p>Kronverkskiy, 49, St. Petersburg, 197101</p></bio><xref ref-type="aff" rid="aff-1"/></contrib></contrib-group><aff-alternatives id="aff-1"><aff xml:lang="en">ITMO University<country>Russian Federation</country></aff></aff-alternatives><pub-date pub-type="collection"><year>2019</year></pub-date><pub-date pub-type="epub"><day>05</day><month>08</month><year>2025</year></pub-date><volume>10</volume><issue>4</issue><elocation-id>398–401</elocation-id><permissions><copyright-statement>Copyright &amp;#x00A9; Gaidash A.A., Medvedeva S.S., Miroshnichenko G.P., 2025</copyright-statement><copyright-year>2025</copyright-year><copyright-holder xml:lang="ru">Gaidash A.A., Medvedeva S.S., Miroshnichenko G.P.</copyright-holder><copyright-holder xml:lang="en">Gaidash A.A., Medvedeva S.S., Miroshnichenko G.P.</copyright-holder><license license-type="creative-commons-attribution" xlink:href="https://creativecommons.org/licenses/by/4.0/" xlink:type="simple"><license-p>This work is licensed under a Creative Commons Attribution 4.0 License.</license-p></license></permissions><self-uri xlink:href="https://nanojournal.ifmo.ru/jour/article/view/511">https://nanojournal.ifmo.ru/jour/article/view/511</self-uri><abstract><p>In this paper, we study unambiguous state discrimination regarding advanced attack on phase-coded quantum key distribution protocol. We propose the method of optimal unambiguous state discrimination probability derivation as a function of a priori probabilities for signal states. The expression obtained as an example in case of two signal states explicitly demonstrates the additional term dependent on small deviations from equal a priori probabilities that may take place in real quantum key distribution implementations. Precise estimation of optimal unambiguous state discrimination probability is significant for complete evaluation of quantum key distribution security.</p></abstract><kwd-group xml:lang="en"><kwd>quantum key distribution</kwd><kwd>unambiguous state discrimination</kwd></kwd-group><funding-group xml:lang="en"><funding-statement>This work was financially supported by the Ministry of Education and Science of Russian Federation (contract No. 03.G25.31.0229).</funding-statement></funding-group></article-meta></front><back><ref-list><title>References</title><ref id="cit1"><label>1</label><citation-alternatives><mixed-citation xml:lang="ru">Bennett C.H., Brassard G. Quantum Cryptography: Public Key Distribution and Coin Tossing. Proceedings of ”International Conference on Computers, Systems and Signal Processing”, Bangalore, India, 09.12.1984, P. 17.</mixed-citation><mixed-citation xml:lang="en">Bennett C.H., Brassard G. Quantum Cryptography: Public Key Distribution and Coin Tossing. 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