Researchers at the LIGO Project Demonstratehow the ultra-fine tuning of devices allows them to push the boundaries of the fundamental laws of physics. The Laser Interferometric Gravitational Wave Observatory (LIGO) detects gravitational waves resulting from catastrophic events in the universe, such as the fusion of neutron stars and black holes. These spatio-temporal vibrations allow scientists to observe gravitational effects under extreme conditions and to explore fundamental questions about the universe and its history. Recently, scientists have registered the movement of a massive object - the detector's mirror - under the influence of quantum effects. But what does this mean?
What is quantum noise?
Recently, physicists have been able to measure the hugeLIGO detector mirrors, the weight of which reaches forty kilograms. Recall that the international research group LIGO includes about 40 research institutes, and more than 600 scientists work on the analysis of data from the detector and other observatories. The main objective of LIGO is the detection and registration of gravitational waves of cosmic origin, which were first predicted by Albert Einstein in General Relativity (GTR) in 1916.
As a study published in Nature magazine showed, 40 kg LIGO mirrors can move in response to tiny quantum effects called quantum noise. In physics, quantum noise refers touncertainties of a physical quantity due to its quantum origin. In general, quantum noise is one of the fundamental quantum laws: the Heisenberg uncertainty principle, according to which some physical quantities cannot simultaneously have absolutely exact values.
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In simple words, some quantitiesimpossible to measure, because the physical laws do not allow this. In practice, this means that in the data of any measuring device there is a quantum noise that is so small that it is lost in more powerful noises, and it cannot be eliminated. However, physicists were able to measure the tiny shift of the forty-kilogram mirror of the LIGO detector. To better understand what is happening, imagine that a fixed shift is several times smaller than a hydrogen atom. But why is this fixed “quantum tremor” important for modern science?
How does LIGO work?
Since the Heisenberg uncertainty principlestates that it is impossible to measure a pair of physical quantities with absolute accuracy, uncertainty, nevertheless, can be reduced in one of them, while increasing in the other. This is exactly what physicists did in the course of the study - they reduced the quantum noise and checked whether the total noise from all sources had changed, and if so, how. To do this, they used a special device with which they were able to measure the contribution of quantum noise to the displacement of LIGO mirrors.
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Recall that in the core of the LIGO detectors are laser interferometers of kilometer scale, which measure the distance between 40 kg pendant mirrors with the best accuracy ever achieved. An unprecedented level of sensitivity of LIGO is achieved thanks to the most advanced technology necessary to suppress vibration and thermal noise in the detectors. It is at these levels of sensitivity that quantum mechanics comes into play: the researchers used the pressure of light on the mirrors and the number of photons in the laser beam. The position of the mirrors is important here, since only the first of two quantities exerts an influence on them.
It is important to understand that the laws of quantum mechanics are the basis of modern technologies including a computer, smartphone and any electrical appliance. We know that quantum laws work.
Thus, the researchers were able to prove that LIGO quantum noise is the uncertainty in the pressure of light. All of the above means that at the LIGO training ground, physicists were able to look below the so-called standard quantum limit - the limit when only natural quantum states are used in measurements.
The experiment used a non-classical"Squeezed light", which reduces the quantum fluctuations of the laser field. Just a few years ago, this type of quantum behavior would be too weak to be observed. But new methods of measurement allow us to expand the horizons of physics, and future improvements and modernization of instruments will allow us to achieve improved sensitivity of existing instruments. This means that in the future we will be able to create gravitational-wave technologies that will allow us to penetrate into space-time in more detail and discover the dizzying secrets of the Universe. So a series of fascinating scientific discoveries awaits us.