PHOTONICS INSIGHTS quantum correlations
Using quantum correlations to study black holes: squeezing techniques for quantum noise reduction in gravitational wave detectors
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Eleonora CAPOCASA *, Matteo BARSUGLIA Université Paris Cité, CNRS, Astroparticule et Cosmologie, F-75013 Paris, France * eleonora. capocasa @ u-paris. fr
“ Experimenters might then be forced to learn how to very gently squeeze the vacuum before it can contaminate the light in the interferometer.”
Carlton Caves, 1981
Since 2015, the gravitational-wave detectors LIGO and Virgo have opened a new window on the universe, detecting hundreds of signals and launching a new era of astronomy with profound impact on relativity, astrophysics, and cosmology. To listen deeper into the cosmos, detectors must become increasingly sensitive. One of the main limitations is quantum noise, ultimately arising from vacuum fluctuations entering the instrument. By“ squeezing” this vacuum, i. e. manipulating its noise properties, LIGO and Virgo have already extended their reach by up to 65 %, revealing events that would otherwise remain hidden. This article provides an overview of squeezing techniques for gravitational-wave detectors, from their origins to the most recent advances.
https:// doi. org / 10.1051 / photon / 202513454
This is an Open Access article distributed under the terms of the Creative Commons Attribution License( https:// creativecommons. org / licenses / by / 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
In April 2019, the gravitational-wave detectors LIGO and Virgo switched on for their 3rd observation run( O3) after a period of upgrade which allowed them to consistently increase their astrophysical reach. Among the many actions taken during the break, the most remarkable was the injection of a specially prepared quantum state, known as squeezed vacuum. Thanks to this technique, quantum noise, which is the primary factor limiting the instrument’ s sensitivity, was significantly reduced, allowing the detectors to observe over 50 % more black hole mergers. In other words, out of every 10 black holes detected, 3 are observable specifically because of vacuum injection. Although counterintuitive, squeezing injection is arguably the most impactful application of quantum vacuum fluctuations developed to date. An unconventional economist might even venture to quantify, in millions of euros, the value of the vacuum itself.
The technique relies on manipulating quantum fluctuations to redistribute uncertainty between the quadratures of the optical field. To understand how vacuum allows us to observe more distant gravitational wave sources, we need to take a step back and address the two theories that revolutionized physics in the 20th century: general relativity and quantum mechanics. Let’ s begin with the first. In 1915, Albert Einstein, predicted that spacetime is curved, revolutionizing our
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