LIGO team improves detection of gravitational waves with compressed light

A team of researchers from the Laser Interferometer Gravitational-Wave Observatory (LIGO), in the United States, has developed what they describe as a compressed light system to improve detection sensitivity.

In their article published in the journal Sciencethe group describes how they made changes to the observatory that reduced flicker, leading to an increase in the number of gravitational waves detected.

Yoichi Aso of the National Astronomical Observatory of Japan published a Perspective article in the same journal explaining how LIGO works and why the team working on it was able to improve the observatories’ sensitivity.

In 2017, a team from Caltech was awarded the Nobel Prize in Physics for their work that led to the development of LIGO and the eventual detection of gravitational waves in 2015. Such ripples in the fabric of space confirmed theories proposed at the originally by Albert Einstein. Since then, the LIGO team has continued to detect gravitational waves while working to improve its detection capabilities.

The LIGO observatory works by splitting a laser beam and sending the results down two long tunnels perpendicular to each other, then sending them back using mirrors. The differences in the beams are evidence of gravitational waves: they expand space-time in the arms that hold the tunnels.

Since its construction, LIGO scientists have known that determining the difference between gravitational waves and flickers in quantum fields can be problematic, and for this reason they have worked to improve the sensitivity.

In this new effort, the team added a specially designed crystal to the detector, as well as new mirrors and several lenses. In doing so, they were able to “squeeze” the light from the beams into a quantum state, resulting in reduced flicker.

Initial tests showed that the improvements only helped detect additional gravitational waves at high frequencies. This led to modifications allowing the detection of additional gravitational waves at lower frequencies.

Together, these improvements had what the team describes as a “stunning effect”: the number of gravitational waves detected suddenly doubled. And that, they noted, allows them to study larger parts of the universe. They suspect these improvements will enable new sciences, such as the study of black holes that merged almost to the time the first stars formed.

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