{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,5]],"date-time":"2026-05-05T08:27:14Z","timestamp":1777969634013,"version":"3.51.4"},"reference-count":44,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2026,5,4]],"date-time":"2026-05-04T00:00:00Z","timestamp":1777852800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Quantum Science and Technology-National Science and Technology Major Project","award":["2021ZD0300800"],"award-info":[{"award-number":["2021ZD0300800"]}]},{"name":"Quantum Science and Technology-National Science and Technology Major Project","award":["2023ZD0300100"],"award-info":[{"award-number":["2023ZD0300100"]}]},{"name":"Key Area R&D Program of Guangdong Province","award":["2020B0303010001"],"award-info":[{"award-number":["2020B0303010001"]}]},{"name":"Taishan Scholars Program"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>Entanglement is one of the most striking phenomena in quantum physics, playing important roles in fundamental physics and quantum information science. It enables a secure means of communication\u2014quantum cryptography\u2014and builds up the foundation of its unconditional security. Entanglement-based quantum cryptography has received great attention from the early demonstrations to the recent remarkable achievements. In a practical scenario, although entanglement-based quantum cryptography can provide inherent source-independent security, its detection side has been shown to be vulnerable to external probing attacks. Here we show that entanglement swapping can effectively solve this critical issue, enabling a side-channel-free quantum cryptography.Entanglement swapping allows each user\u2019s quantum state preparation and detection in a completely private station, which is immune to any external probing side channels. We demonstrate the entanglement-swapping quantum cryptography scheme in the field based on two independent entanglement photon sources. Based on the remote entangled photon pairs, we implement the Ekert-1991 protocol under a channel attenuation equivalent to 100 km of standard optical fiber, achieving a Bell violation value of S=2.659\u00b10.092 and a secret key rate of 0.0163 bit\/s. While recent device-independent QKD demonstrations have reached 100 km using atoms or ions, our photonic ES-QKD offers a complementary, all-optical pathway that is directly compatible with existing fiber networks and quantum repeaters.<\/jats:p>","DOI":"10.3390\/e28050518","type":"journal-article","created":{"date-parts":[[2026,5,5]],"date-time":"2026-05-05T07:57:29Z","timestamp":1777967849000},"page":"518","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Entanglement Swapping Enables the Practical Security of Quantum Cryptography"],"prefix":"10.3390","volume":"28","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-7064-5811","authenticated-orcid":false,"given":"Yang-Fan","family":"Jiang","sequence":"first","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"},{"name":"Jinan Institute of Quantum Technology, Jinan 250101, China"},{"name":"Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Liang","family":"Huang","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"},{"name":"China Telecom Quantum Information Technology Group Co., Ltd., Hefei 230088, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yu-Zhe","family":"Zhang","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-8787-1595","authenticated-orcid":false,"given":"Likang","family":"Zhang","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Qi-Chao","family":"Sun","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"},{"name":"Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China"},{"name":"Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Zheng-Ping","family":"Li","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"},{"name":"Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6946-4362","authenticated-orcid":false,"given":"Hao","family":"Li","sequence":"additional","affiliation":[{"name":"Shanghai Key Laboratory of Superconductor Integrated Circuit Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Weijun","family":"Zhang","sequence":"additional","affiliation":[{"name":"Shanghai Key Laboratory of Superconductor Integrated Circuit Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Lixing","family":"You","sequence":"additional","affiliation":[{"name":"Shanghai Key Laboratory of Superconductor Integrated Circuit Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1643-225X","authenticated-orcid":false,"given":"Feihu","family":"Xu","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"},{"name":"Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China"},{"name":"Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Qiang","family":"Zhang","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"},{"name":"Jinan Institute of Quantum Technology, Jinan 250101, China"},{"name":"Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China"},{"name":"Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6100-5142","authenticated-orcid":false,"given":"Jian-Wei","family":"Pan","sequence":"additional","affiliation":[{"name":"Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China"},{"name":"Hefei National Laboratory, University of Science and Technology of China, Hefei 230088, China"},{"name":"Shanghai Research Center for Quantum Science and CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Shanghai 201315, China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,5,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"130502","DOI":"10.1103\/PhysRevLett.108.130502","article-title":"Side-channel-free quantum key 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