The US-based Laser Interferometer Gravitational-wave Observatory (LIGO) used to pick up whispers of gravitational waves from space every month or so, but now it’s happening nearly every week thanks to “the squeezer”.
Officially the “quantum vacuum squeezer”, this new instrument takes out quantum noise, the infinitesimally small fluctuations in the vacuum of space that can muddy or even completely mask incoming signals.
It was designed, built and integrated with LIGO’s detectors by researchers from the Massachusetts Institute of Technology (MIT) Caltech in the US and the Australian National University, who detail its workings in a paper in the journal Physical Review Letters.
“Where quantum mechanics comes in relates to the fact that LIGO’s laser is made of photons,” says lead author Maggie Tse from MIT.
“Instead of a continuous stream of laser light, if you look close enough it’s actually a noisy parade of individual photons, each under the influence of vacuum fluctuations. Whereas a continuous stream of light would create a constant hum in the detector, the individual photons each arrive at the detector with a little pop.”
Thanks to the squeezer, LIGO has shaved down this confounding quantum crackle, extending the detectors’ range by 15%.
Combined with an increase in laser power, this means the detectors can pick out a gravitational wave generated by a source in the Universe more than 400 million light-years away.