{"id":21958,"date":"2025-07-25T02:06:11","date_gmt":"2025-07-25T02:06:11","guid":{"rendered":"https:\/\/www.newsbeep.com\/ca\/21958\/"},"modified":"2025-07-25T02:06:11","modified_gmt":"2025-07-25T02:06:11","slug":"imaginary-time-delays-are-for-real","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ca\/21958\/","title":{"rendered":"Imaginary Time Delays Are For Real"},"content":{"rendered":"

July 24, 2025&bullet; Physics 18, s95<\/p>\n

The time delay experienced by a scattered light signal has an imaginary part that was considered unobservable, but researchers have isolated its effect in a frequency shift.<\/p>\n

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A scattering material, such as a frosted window or a thin fog, will cause light to travel slower than it would if no material were in its path. The mathematical formula for this time delay has a real part\u2014which is well studied\u2014and a lesser-known imaginary part. \u201cThe imaginary time delay has been largely ignored and disregarded as unphysical,\u201d says Isabella Giovannelli from the University of Maryland. But she and her advisor Steven Anlage have now measured this abstract quantity by recording a corresponding frequency shift in scattered light pulses [1<\/a>].<\/p>\n

The real part of the time delay has been observed in many experiments, particularly slow-light setups where light pulses can become effectively trapped inside a scattering medium (see Focus: Light Nearly Stopped in a Waveguide<\/a>). By contrast, the imaginary part has been stuck in the realm of mathematics. Theoretical work from 2016, however, showed that the imaginary time delay can be related to a potentially observable frequency shift [2<\/a>].<\/p>\n

Giovannelli and Anlage have now uncovered this signal in a system where the frequency shift is expected to be large. As a stand-in for the scattering medium, they used a microwave circuit with a ring graph, which is a simple resonator often used as a filter or a switch. The researchers sent 5-GHz microwave pulses\u2014with a narrow bandwidth of 5 MHz\u2014through the resonator and recorded a shift of 0.48 MHz in the central peak of the pulses. This shift was in close agreement with theoretical predictions.<\/p>\n

The researchers plan to look for similar shifts in more complex pulses, where measurements of the imaginary time delay could offer insights into the effects of scattering media on optical communication signals, Giovannelli says. <\/p>\n

\u2013Michael Schirber<\/p>\n

Michael Schirber is a Corresponding Editor for\u00a0Physics Magazine<\/a> based in Lyon, France.<\/p>\n

ReferencesI. L. Giovannelli and S. M. Anlage, \u201cPhysical interpretation of imaginary time delay,\u201d Phys. Rev. Lett. 135, 043801 (2025)<\/a>.M. Asano et al., \u201cAnomalous time delays and quantum weak measurements in optical micro-resonators,\u201d Nat. Commun. 7, 13488 (2016)<\/a>.Subject AreasRelated Articles\"Photonic<\/a>\"New<\/a>\"Laser<\/a> More Articles<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"July 24, 2025&bullet; Physics 18, s95 The time delay experienced by a scattered light signal has an imaginary…\n","protected":false},"author":2,"featured_media":21959,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[49,48,314,66],"class_list":{"0":"post-21958","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-ca","9":"tag-canada","10":"tag-physics","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/21958","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=21958"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/21958\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/21959"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=21958"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=21958"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=21958"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}