Notizia

Dec 01, 2023

Spremitura quantistica: ai confini della fisica

Di Whitney Clavin, California Institute of Technology (Caltech) 30 luglio 2023 Lee McCuller, professore di fisica ed esperto di spremitura quantistica, sta sviluppando tecniche innovative per migliorare la

Di Whitney Clavin, California Institute of Technology (Caltech), 30 luglio 2023

Lee McCuller, professore di fisica ed esperto di spremitura quantistica, sta sviluppando tecniche innovative per migliorare la sensibilità di LIGO, il rilevatore di onde gravitazionali più avanzato al mondo. La sua ambizione futura è ampliare l'applicazione di queste tecniche oltre LIGO.

Il nuovo professore del Caltech Lee McCuller sta rendendo le misurazioni quantistiche ancora più precise.

Fin dalla giovane età, il nuovo professore assistente di fisica, Lee McCuller, ha apprezzato il processo pratico di costruzione delle cose. Questo interesse è stato favorito da suo zio, che ha creato per lui un alimentatore. McCuller lo ha utilizzato insieme ai kit elettronici per hobby di RadioShack, eseguendo compiti semplici come azionare circuiti analogici per accendere e spegnere luci e motori. Oggi, l'abilità ingegneristica di McCuller è applicata a un dispositivo eccezionalmente avanzato, quello che alcuni chiamerebbero il dispositivo di misurazione più avanzato al mondo: l'Osservatorio delle onde gravitazionali dell'interferometro laser, o LIGO.

Lee McCuller, assistente professore di fisica. Credito: Caltech

McCuller is a recognized expert in a field known as quantum squeezing, a technique utilized at LIGOThe Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory supported by the National Science Foundation and operated by Caltech and MIT. It's designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. It's multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves. It consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">LIGO to achieve extremely precise measurements of gravitational waves. that travel millions and billions of light-years across space to reach us. When black holes and collapsed stars, called neutron stars, collide, they generate ripples in space-time, or gravitational wavesGravitational waves are distortions or ripples in the fabric of space and time. They were first detected in 2015 by the Advanced LIGO detectors and are produced by catastrophic events such as colliding black holes, supernovae, or merging neutron stars." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"> onde gravitazionali. I rilevatori di LIGO, situati a Washington e in Louisiana, sono specializzati nel captare queste onde, ma sono limitati dal rumore quantistico, una proprietà intrinseca della meccanica quantistica che fa sì che i fotoni entrino e escano dall'esistenza nello spazio vuoto. La compressione quantistica è un metodo complesso per ridurre questo rumore indesiderato.

La ricerca sullo spremitura quantistica e sulle misurazioni correlate si è intensificata già negli anni '80, con studi teorici chiave di Kip Thorne (BS '62) del Caltech, Richard P. Feynman, professore emerito di fisica teorica, insieme al fisico Carl Caves (PhD '79). ) e altri in tutto il mondo. Queste teorie hanno ispirato la prima dimostrazione sperimentale della spremitura nel 1986 da parte di Jeff Kimble, il professore emerito di fisica William L. Valentine. I decenni successivi videro molti altri progressi nella ricerca sulla spremitura, e ora McCuller è all’avanguardia in questo campo innovativo. Ad esempio, è stato impegnato a sviluppare la compressione “dipendente dalla frequenza” che migliorerà notevolmente la sensibilità di LIGO quando si riattiverà a maggio di quest'anno.

After earning his bachelor’s degree from the University of Texas at Austin in 2010, McCuller attended the University of ChicagoFounded in 1890, the University of Chicago (UChicago, U of C, or Chicago) is a private research university in Chicago, Illinois. Located on a 217-acre campus in Chicago's Hyde Park neighborhood, near Lake Michigan, the school holds top-ten positions in various national and international rankings. UChicago is also well known for its professional schools: Pritzker School of Medicine, Booth School of Business, Law School, School of Social Service Administration, Harris School of Public Policy Studies, Divinity School and the Graham School of Continuing Liberal and Professional Studies, and Pritzker School of Molecular Engineering." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">University of Chicago, where he earned his PhD in physics in 2015. There he began work on an experiment called the Fermilab Holometer, which looked for a speculative type of noise that would link gravity with quantum mechanics. It was during this project that McCuller met LIGO scientists, including MITMIT is an acronym for the Massachusetts Institute of Technology. It is a prestigious private research university in Cambridge, Massachusetts that was founded in 1861. It is organized into five Schools: architecture and planning; engineering; humanities, arts, and social sciences; management; and science. MIT's impact includes many scientific breakthroughs and technological advances. Their stated goal is to make a better world through education, research, and innovation." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"MIT’s Rai Weiss—who together with Thorne and Barry Barish, the Ronald and Maxine Linde Professor of Physics, Emeritus, won the Nobel Prize in Physics in 2017 for their groundbreaking work on LIGO. McCuller was inspired by Weiss and the LIGO project and decided to join MIT in 2016. He became an assistant professor at Caltech in 2022./p>

Up until now, we have been squeezing light in LIGO to reduce uncertainty in the frequency. This allows us to be more sensitive to the high-frequency gravitational waves within LIGO’s range. But if we want to detect lower frequencies—which occur earlier in, say, a black holeA black hole is a place in space where the gravitational field is so strong that not even light can escape it. Astronomers classify black holes into three categories by size: miniature, stellar, and supermassive black holes. Miniature black holes could have a mass smaller than our Sun and supermassive black holes could have a mass equivalent to billions of our Sun." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"black hole merger, before the bodies collide—we need to do the opposite: we want to make the light’s amplitude, or power, more certain and the frequency less certain. At the lower frequencies, the shot noise, our BB-like photons, push the mirrors around in different ways. We want to reduce that. Our new frequency-dependent cavity at the LIGO detectors is designed to reduce the frequency uncertainty in the high frequencies and the amplitude uncertainties in the low frequencies. The goal is to win everywhere and reduce the unwanted mirror motions./p>

What this means is that we will be even more sensitive to the early phases of black hole and neutron starA neutron star is the collapsed core of a large (between 10 and 29 solar masses) star. Neutron stars are the smallest and densest stars known to exist. Though neutron stars typically have a radius on the order of just 10 - 20 kilometers (6 - 12 miles), they can have masses of about 1.3 - 2.5 that of the Sun." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"neutron star mergers, and that we can see even fainter mergers./p>