We return to a story from last July when the Massachusetts Institute of Technology (MIT) LIGO Laboratory announced that they had successfully detected quantum fluctuations in the positions of the roughly 40kg mirrors that are part of the gravitational wave detectors in the US. These jitters in position are just 10^-20 of a meter – an amount 1000s of millions of times smaller than the size of a hydrogen atom – but they are large enough to place a limit on what kinds of gravitational waves can be detected. 

In a new paper in Physical Review Letters, Fausto Acernese leads a paper replicating these quantum fluctuation measurements with the Virgo Collaboration in the EU. As these 42kg mirrors jitter, they make it impossible to detect low-frequency gravitational waves. This is because Heisenburg’s Uncertainty Principle forces researchers to make choices on where to put their accuracy. To expand what LIGO and Virgo can observe, new technologies that allow lower frequencies to be seen and that move the quantum noise to higher frequencies will be needed. Currently, frequency-dependent systems that will allow tuning are being developed and initial tests have already taken place. Here is to hoping that in the future we’ll have tunable detectors that allow us to see both different-sized quantum jitters and different frequencies of gravitational waves.

More Information

Max Planck Institute press release 

“Quantum Backaction on Kg-Scale Mirrors: Observation of Radiation Pressure Noise in the Advanced Virgo Detector,” F. Acernese et al. (The Virgo Collaboration), 2020 Sep. 22, Physical Review Letters