Two experiments have demonstrated a technique that will help existing gravitational-wave detectors to double their sensitivity.
The detectors, called interferometers, sense ripples in space-time produced by distant cataclysmic events such as collisions of black holes. In each detector, laser light bounces between mirrors at the ends of vacuum pipes several kilometres long.
Interferometers have upped their sensitivity to relatively high-frequency gravitational waves by ‘squeezing the vacuum’ — manipulating the quantum properties of their laser light so that its photons arrive at a sensor more regularly than before. But this can slightly degrade the detector’s sensitivity to lower-frequency gravitational waves.
A type of vacuum squeezing that improves sensitivity at both high and low frequencies has now been demonstrated by Eleonora Capocasa and Matteo Leonardi at the National Astronomical Observatory of Japan in Tokyo and their colleagues, and by a separate team led by Lee McCuller and Christopher Whittle at the Massachusetts Institute of Technology in Cambridge. The technique involves temporarily storing light between auxiliary mirrors in the interferometer. Applying it at existing facilities will require the construction of these mirrors and extra vacuum pipes around 300 metres long.
Correction: An earlier version of this article incorrectly characterized the role of Eleonora Capocasa and Matteo Leonardi.