Gravitational wave detectors are limited by basic quantum noise – an incessant “hum” that they can never remove. Now, physicists have recently improved a technique called “squeezing” that will allow the next generation of detectors to double their sensitivity.
All of the gravitational waves that slosh in the universe are incredibly weak. When they wash over the earth, even the strongest waves wobble no more than the width of an atomic nucleus. Our detectors like LIGO and VIRGO, which reflect laser beams back and forth, have to measure these tiny differences. But when they do, they run into the fundamental uncertainty of the universe dictated by quantum mechanics.
This fundamental uncertainty is known as the Heisenberg uncertainty principle and states that certain series of measurements (e.g. position and momentum of a particle or phase and brightness of a light beam) can never be as precise as we want them to be. This uncertainty limits the size of the gravitational waves that we can capture – they have to be larger than the background quantum noise due to the uncertainty principle.
But physicists are smart people, and they have found a way to trick the uncertainty principle by “squeezing” light. Essentially, the trick works by carefully preparing the light source, which makes the phase measurement more precise (which we use to capture the gravitational waves, which comes with a cost in measuring brightness (which we don’t care much). In this way the general principle of uncertainty is respected while the observations become more precise.
The team of a laser experiment, GEO600, was able to reduce the basic quantum noise by a factor of two. If your system was in some kind of LIGO, LIGO could detect gravitational waves twice as weakly, which increases the instrument’s ability to observe.
“We concentrated on optimizing and characterizing the squeezed light source on the GEO600 and its interface to the detector. Compared to a detector without squeezing, the observable volume of the universe has increased by a factor of 8 at high frequencies. This could help improve our understanding of neutron stars, ”says Dr. James Lough, Senior Scientist for GEO600 and lead author of the paper published in Physical Review Letters.
This technology is needed to enable the next generation of detectors. “The international community is currently planning the third generation of gravitational wave detectors: the European Einstein telescope and Cosmic Explorer in the USA. Both require even more pressure than the impressive results we have achieved. GEO600 is in the ideal position to further optimize this technology ”, says Prof. Karsten Danzmann, Director at AEI and Director of the Institute for Gravitational Physics at Leibniz University Hannover.
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