Physicists used LIGO’s mirrors to approach a quantum limit

A big item has approached a world normally reserved for the tiniest of creatures.

Scientists quieted the relative movements of the mirrors (one shown) of the Advanced Laser Interferometer Gravitational-Wave Observatory, putting them in a near-quantum state.

CALTECH, MIT, LIGO LAB

Quantum mechanics is most commonly used to describe very small objects such as atoms, electrons, and other subatomic particles. However, physicists have now succeeded in bringing the equivalent of a 10-kilogram object near the quantum realm's edge.

Using the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, scientists were able to minimise vibrations in a combination of the facility's mirrors to virtually the lowest level possible by quantum mechanics.

The researchers were able to eliminate disparities in the jiggling of LIGO's four 40-kilogram mirrors, bringing them close to perfect synchronisation. When the mirrors are arranged in this manner, they act as a single 10-kilogram object.

LIGO is a gravitational wave detector that uses laser light to bounce between sets of mirrors in the detector's two long arms to detect gravitational waves (SN: 2/11/16). MIT physicist Vivishek Sudhir and colleagues, on the other hand, employed laser light to precisely monitor the mirrors' movements and use electric fields to counteract them. Sudhir describes it as "almost like a noise-canceling earphone." The technique, however, cancels off motion rather than measuring neighbouring sounds and cancelling them out.

The researchers were able to lower the relative motions of the mirrors to around 10.8 phonons, or quantum units of vibration, which is near to the zero-phonon quantum limit.

The goal of the research isn't to better understand gravitational waves, but to get closer to unlocking quantum mechanics secrets. Scientists are still trying to figure out why huge objects don't always obey quantum mechanics' rules. Such objects decohere, or lose their quantum features. Scientists may be able to learn more about how decoherence occurs by studying quantum states of larger objects.

In quantum states, much smaller objects have been observed in previous studies. Physicist Markus Aspelmeyer of the University of Vienna and colleagues succeeded in bringing nanoparticle vibrations to the quantum limit (SN: 1/30/20) in 2020. According to Aspelmeyer, LIGO's mirrors offer "a terrific setup for studying decoherence effects on super-massive objects in the quantum regime."