Illinois physicists propose quantum-limited gravitational wave detector

A team of researchers from Illinois Physics in The Grainger College of Engineering at the University of Illinois Urbana-Champaign, the Lawrence Berkeley National Laboratory, and the Austrian Academy of Sciences has proposed a novel design for gravitational wave detection based on superconducting magnetic levitation. Their findings, published in Physical Review Letters, introduce the possibility of observing gravitational waves at frequencies between 1 kilohertz and 1 megahertz.

“Gravitational waves are a really interesting probe of new physics,” says Michael Wentzel, an Illinois Physics doctoral student and the paper’s lead author. “They couple to everything that has mass, which makes them a great way to detect physics that don’t interact with other forces in the standard model.”

Additionally, because the gravitational force is much weaker than the electromagnetic force, gravitational wave observations could potentially allow scientists to directly probe times much closer to the Big Bang compared to electromagnetic observations. However, current gravitational wave searches primarily focus on low-frequency waves.

For years, Wentzel and his colleagues had been interested in detecting high-frequency gravitational waves. Wentzel began by reverse engineering a previous project that utilized a hollow sphere containing an electromagnetic field: what would happen if they turned the scenario inside out and used a solid sphere with a magnetic field on the outside?

The researchers’ calculations led them to propose a theoretical superconducting magnetic levitation system. Inside a vacuum, a levitated sphere of lead placed between two fixed electromagnets—known as solenoids—would respond to spacetime strain from a gravitational wave by oscillating relative to the solenoids, inducing a current that could be read by a quantum-limited amplifying circuit.

“When a gravitational wave hits the sphere, the sphere wiggles,” Wentzel says. “By determining how much the sphere moves, we can determine the strength and frequency of the gravitational wave and look for new physics to determine its source.”

Although previous research has investigated levitated systems and amplifying circuits separately, the researchers’ proposed experiment combines these two technologies and demonstrates that the system could operate in a high-frequency regime.

And while currently theoretical, the researchers would ultimately like the experiment to be fully realized.

“There are a lot of people using parts of this proposal for other applications; for dark matter searches in particular,” Wentzel explains. “It would be really interesting if we could get somebody to create a dedicated search for these high-frequency gravitational waves.”