Particle physics experiments

Macroscopic quantum mechanics in gravitational wave experiments

Quantum physics experiments exploring the movement of macroscopic or heavy bodies under gravitational forces require protection against any environmental noise and very efficient detection.

An ideal system is a highly reflective mirror whose movement is detected by monochromatic light, which is detected photoelectrically with high quantum efficiency. A quantum optomechanical experiment is performed if the quantum uncertainties of light and mirror motion influence each other, ultimately leading to the observation of an entanglement between optical and kinetic degrees of freedom.

In AVS Quantum Science, co-published by AIP Publishing and AVS, researchers from the University of Hamburg in Germany examine research on gravitational wave detectors as a historical example of quantum technologies and examine fundamental research on the link between quantum physics and gravity. Gravitational wave astronomy requires unprecedented sensitivities to measure the tiny spatiotemporal oscillations at frequencies in the audio band and below.

The team looked at recent gravitational wave experiments showing that it is possible to shield large objects, such as a 40-kilogram quartz glass mirror reflecting 200 kilowatts of laser light, from the strong influences of the thermal and seismic environment to allow them to evolve as a quantum object.

“The mirror only perceives light, and the light only the mirror. The environment is basically not there for both of them”, said author Roman Schnabel. “Their joint evolution is described by the Schrödinger equation.”

This decoupling from the environment, which is at the heart of all quantum technologies, including the quantum computer, enables measurement sensitivities that would otherwise be impossible.

The researchers’ review overlaps with the work of Nobel laureate Roger Penrose on exploring the quantum behavior of massive objects. Penrose sought to better understand the link between quantum physics and gravity, which remains an open question.

Penrose thought of an experiment in which light would be coupled to a mechanical device via radiation pressure. In their review, the researchers show that while these very fundamental questions in physics remain unresolved, coupling highly shielded bulk devices that reflect laser light is beginning to improve sensor technology.

In the future, researchers will likely further explore the decoupling of gravitational wave detectors from environmental influences.

More broadly, the decoupling of quantum devices from any thermal energy exchange with the environment is key. It is required for quantum measuring devices as well as quantum computers.

The article “Macroscopic quantum mechanics in gravitational wave observatories and beyond” is written by Roman Schnabel and Mikhail Korobko. The article will appear in AVS Quantum Sciences March 15, 2022 (DOI: 10.1116/5.0077548). After that date, it can be viewed at