Physicists Have Seen The Effect Of Quantum Fluctuations On A Macroscopic Object
The LIGO collaboration was the first to directly measure the effect of quantum fluctuations on a macroscopic object — a mirror weighing 40 kilograms. The work is available in the journal Nature.
One of the most surprising predictions of quantum field theory is that the vacuum of space is not empty, but filled with virtual particles that are born and die due to quantum fluctuations. Although these fluctuations are very weak, scientists can measure their effect on fields or small objects. However, in everyday life, when dealing with macroscopic systems, we are not able to directly feel the influence of quantum fluctuations.
The LIGO Observatory, where gravitational waves were first detected, is one of the most accurate installations in the world. The Observatory consists of two huge detectors, which are four-kilometer interferometers with mirrors weighing 40 kilograms. During the measurement of gravitational waves, a laser beam is sent to the interferometer, reflected from mirrors, and returned. On the time delay, it is possible to know whether there has been a displacement of the mirrors due to gravitational waves.
The developed detector system is very well protected from external noise, but it is completely impossible to get rid of quantum noise due to fluctuations. On the other hand, with such good protection from classical noise, it is possible to measure the effect of quantum effects in a macroscopic system.
The LIGO collaboration reported that for the first time they were able to detect the effect of quantum fluctuations on a macroscopic interference pattern, namely, the displacement of the mirror. Previously, scientists were able to see the effect of fluctuations only on nanoobjects billions of times smaller.
To detect the direct action of fluctuations, scientists introduced a device based on quantum compression into the scheme, which allowed changing the properties of fluctuations, namely the strength of quantum correlations. To do this, scientists created a compressed state of light, with a controlled compression structure, and used it in an interferometer as a test beam. Physicists varied the compression parameters and removed the dependence of the mirror displacement on these parameters. If there were no quantum correlations, the displacement of the mirror would be insensitive to compression. Thus, they were able to reliably show that the displacement of mirrors is due to quantum noise, and not ordinary vibrations.
The researchers registered a mirror offset of 10-20 meters, which is an absolute record when measuring mechanical movement. Quantum compressed light can also be used in the future for even more accurate measurements of gravitational waves. This method allows measurements to be made with an accuracy higher than the quantum limit.
In March, LIGO stopped its work due to the pandemic, but now they are ready to continue working on the installation.