{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,20]],"date-time":"2026-03-20T07:30:38Z","timestamp":1773991838402,"version":"3.50.1"},"reference-count":33,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2024,3,29]],"date-time":"2024-03-29T00:00:00Z","timestamp":1711670400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"QUANCOM project","award":["2014\u20132020 ARS01 00734"],"award-info":[{"award-number":["2014\u20132020 ARS01 00734"]}]},{"name":"Italian Space Agency","award":["2014\u20132020 ARS01 00734"],"award-info":[{"award-number":["2014\u20132020 ARS01 00734"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The application of statistical estimation theory to Hong\u2013Ou\u2013Mandel interferometry led to enticing results in terms of the detection limit for photon reciprocal delay and polarisation measurement. In the following paper, a fully fibre-coupled setup operating in the telecom wavelength region proves to achieve, for the first time, in common-path Hong\u2013Ou\u2013Mandel-based interferometry, a detection limit for photon phase delay at the zeptosecond scale. The experimental results are then framed in a theoretical model by calculating the Cramer\u2013Rao bound (CRB) and, after comparison with the obtained experimental results, it is shown that our setup attains the optimal measurement, nearly saturating CRB.<\/jats:p>","DOI":"10.3390\/s24072202","type":"journal-article","created":{"date-parts":[[2024,3,31]],"date-time":"2024-03-31T13:32:56Z","timestamp":1711891976000},"page":"2202","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Photon Phase Delay Sensing with Sub-Attosecond Uncertainty"],"prefix":"10.3390","volume":"24","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0924-0698","authenticated-orcid":false,"given":"Fabrizio","family":"Sgobba","sequence":"first","affiliation":[{"name":"Italian Space Agency (ASI), Space Geodesy Centre \u2018Giuseppe Colombo\u2019, Localit\u00e0 Terlecchia, 75100 Matera, MT, Italy"},{"name":"National Council for Research-National Institute of Optics (CNR-INO), Via Campi Flegrei n. 34, 80078 Pozzuoli, NA, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7603-8537","authenticated-orcid":false,"given":"Andrea","family":"Andrisani","sequence":"additional","affiliation":[{"name":"Italian Space Agency (ASI), Space Geodesy Centre \u2018Giuseppe Colombo\u2019, Localit\u00e0 Terlecchia, 75100 Matera, MT, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0898-3569","authenticated-orcid":false,"given":"Luigi","family":"Santamaria Amato","sequence":"additional","affiliation":[{"name":"Italian Space Agency (ASI), Space Geodesy Centre \u2018Giuseppe Colombo\u2019, Localit\u00e0 Terlecchia, 75100 Matera, MT, Italy"},{"name":"National Council for Research-National Institute of Optics (CNR-INO), Via Campi Flegrei n. 34, 80078 Pozzuoli, NA, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2024,3,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"2044","DOI":"10.1103\/PhysRevLett.59.2044","article-title":"Measurement of subpicosecond time intervals between two photons by interference","volume":"59","author":"Hong","year":"1987","journal-title":"Phys. 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