A tiny detector could unveil gravitational waves we’ve never seen before

Gravitational waves, the ripples in spacetime predicted by Einstein, have already been detected in high-frequency ranges using ground-based observatories such as LIGO and Virgo, and in extremely low frequencies through pulsar timing arrays. Yet a large "mid-band" region has remained undetected until now.

Compact Design Targets a Missing Frequency Range

A research team from the Universities of Birmingham and Sussex has proposed a compact new detector that relies on optical cavity and atomic clock technologies to identify gravitational waves within the elusive milli-Hertz band (10⁻⁵ - 1 Hz).

In a study published on October 3 in Classical and Quantum Gravity, the scientists describe how their design uses advanced optical resonator systems, originally developed for optical atomic clocks, to detect the minute changes in laser light caused by passing gravitational waves. Unlike the enormous interferometers currently used, this setup is small enough to fit on a lab table and is largely unaffected by seismic and Newtonian noise.

Bringing Cosmic Detection to the Laboratory

Co-author Dr. Vera Guarrera from the University of Birmingham explained: "By using technology matured in the context of optical atomic clocks, we can extend the reach of gravitational wave detection into a completely new frequency range with instruments that fit on a laboratory table. This opens the exciting possibility of building a global network of such detectors and searching for signals that would otherwise remain hidden for at least another decade."

The milli-Hertz frequency range, often referred to as the "mid-band," is believed to contain signals from a variety of astrophysical and cosmological events, including mergers between white dwarfs and black holes. Large space-based missions such as LISA are designed to explore these frequencies, but their launches are not expected until the 2030s. The new optical resonator detectors could begin probing this territory much sooner.

Co-author Professor Xavier Calmet from the University of Sussex added: "This detector allows us to test astrophysical models of binary systems in our galaxy, explore the mergers of massive black holes, and even search for stochastic backgrounds from the early universe. With this method, we have the tools to start probing these signals from the ground, opening the path for future space missions."

Ready to Explore Before Space Missions Launch

While future space-based observatories like LISA will eventually provide greater sensitivity, the newly proposed optical cavity detectors offer an immediate and cost-effective option for investigating the milli-Hertz band. The researchers also suggest that connecting these detectors to existing clock networks could extend their sensitivity to even lower frequencies, complementing the higher-frequency capabilities of facilities such as LIGO.

Each proposed detector consists of two ultrastable optical cavities arranged at right angles and paired with an atomic frequency reference. This design enables multiple detection channels, increasing sensitivity and allowing scientists to identify both the polarization and direction of gravitational wave sources.