Happy marriage between quantum mechanics and relativity

The Virgo and LIGO instruments benefit from a quantum optics technique in gravitational wave detection.

By David Larousserie Posted today at 06:00

Time to Reading 4 min.

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1st In April, the three major "telescopes" that were the first to discover in September 2015 extraterrestrial signals of a new type have returned to service after a year and a half of work to double their performance. These signals are gravitational waves, space-time vibrations caused by giant astrophysical phenomena, such as the fusional rotation of a pair of black holes as large as several tens of Sun, or the violent collision between two neutron stars ( very compact stars), ten times lighter.

Even before the instruments LIGO (two telescopes in the United States) and Virgo (in Italy) were again agitated by such tremors, they performed a pretty feat: the reconciliation of the two great theories of modern physics, deemed incompatible , quantum mechanics and general relativity. The first, developed in the 1920s, describes the world of particles. The second, developed by Albert Einstein in 1915, is perfect for understanding massive objects such as stars or galaxies. But since too much matter is concentrated in a small region, like in a black hole, the two theories do not stick together …

Increase the accuracy of the detectors

Now LIGO and Virgo have made this impossible marriage possible by using quantum mechanics to identify phenomena of general relativity. "An entire branch of physics, quantum optics, has been developed to be applied to the detection of gravitational waves, underlines Antoine Heidmann, director of the Kastler-Brossel laboratory (LKB) (CNRS, Sorbonne University, Collège de France). And that as early as the 1980s. " This branch branched out into communication, computing or quantum information.

At the time, the goal was to increase the accuracy of gravitational wave detectors, because the sources of such vibrations may be enormous, they only fine lines on the surface of space-time. Arrived on Earth, they move objects less than a thousandth of the diameter of a proton. Suffice to say a lapping in a sea dismounted. But even after having dampened all the external disturbances, it remains the irreducible, the equivalent of a foam of quantum origin. That is to say the intrinsic phenomena to the material, which will disturb the measurements. For example, in a laser beam, like those used by LIGO and Virgo, the number of grains of light, the photons, is variable and random, invariably causing fluctuations in the measurements.

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