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 by Staff Writers Hannover, Germany (SPX) Sep 23, 2020
Quantum mechanics does not only describe how the world works on its smallest scales, but also affects the motion of macroscopic objects. An international research team, including four scientists from the MPI for Gravitational Physics (Albert-Einstein-Institut/AEI) and Leibniz University in Hannover, Germany, has shown how they can influence the motion of mirrors, each weighing more than 40 kg, in the Advanced Virgo gravitational-wave detector trough the deliberate use of quantum mechanics. At the core of their experiment published in Physical Review Letters is a squeezed-light source, developed and built at the AEI in Hanover, which generates specially tuned laser radiation and improves the detector's measurement sensitivity during observing runs. The quantum mechanical world of probabilities and uncertainties also governs the behavior of the kilometer-sized gravitational wave detectors Advanced LIGO, Advanced Virgo, and GEO600. The sensitivity of these high-precision instruments to gravitational waves - caused, for example, by distant black hole mergers - is currently limited by quantum mechanical background noise.
Heisenberg's Uncertainty Limits the Detectors The reason for this is Heisenberg's uncertainty principle. According to this cornerstone of quantum mechanics, simultaneous measurements of two related quantities are impossible with arbitrary accuracy; they are blurred, or uncertain. However, the measurement inaccuracy of one of the two quantities can be reduced - but only at the expense of a greater inaccuracy when measuring the other quantity. In gravitational wave detectors shot noise - the patter of the randomly and irregularly arriving light particles - is usually reduced. This trick is necessary because this quantum mechanical background noise limits the sensitivity of the detectors at high measuring frequencies with which they listen into the cosmos.
There Ain't No Such Thing as a Free Lunch "There ain't no such thing as a free lunch: If you reduce the quantum mechanical background noise at high frequencies using current squeezed-light sources, you pay a price. And this price is increased quantum noise - and thus reduced measurement accuracy - at lower frequencies," explains Moritz Mehmet, researcher at the AEI Hannover.
Massive Mirrors Move "If we use particularly strongly squeezed light, we clearly see an additional jitter of the 42 kilogram mirrors in the Advanced Virgo detector - really macroscopic objects - at low frequencies. This is due to quantum mechanical effects," says Henning Vahlbruch, a researcher at the AEI Hannover. This new measurement is only possible because the researchers are able to determine fluctuations of the mirror positions to less than a thousandth of a proton diameter. Previous measurements of this effect in laboratory experiments used masses that were 10 million times lighter than the Advanced Virgo mirrors.
Squeezed-Light Pioneer GEO600 In the future, squeezed-light sources will have to be modified to further increase the sensitivity of gravitational-wave detectors. The carefully tuned laser radiation they generate must no longer be the same at all frequencies. Its properties must be adjusted so that it reduces quantum mechanical noise at both high and low frequencies. The development of this frequency-dependent squeezing is already underway in the worldwide community of gravitational wave researchers including GEO600. Two groups have shown first successful experimental demonstrations in spring 2020.
Research Report: "Quantum Backaction on Kg-Scale Mirrors: Observation of Radiation Pressure Noise in the Advanced Virgo Detector"
Physicists make electrical nanolasers even smaller Moscow, Russia (SPX) Sep 17, 2020 Researchers from the Moscow Institute of Physics and Technology and King's College London cleared the obstacle that had prevented the creation of electrically driven nanolasers for integrated circuits. The approach, reported in a recent paper in Nanophotonics, enables coherent light source design on the scale not only hundreds of times smaller than the thickness of a human hair but even smaller than the wavelength of light emitted by the laser. This lays the foundation for ultrafast optical data transfe ... read more
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