Coin-sized device could detect gravitational waves

Physicists from The University of Western Australia (UWA) have invented a tiny detector, about the size of a coin, which they claim could observe gravitational waves - ripples in space-time generated by accelerating massive objects. The waves have been predicted by Einstein’s general theory of relativity but are yet to be directly observed.

Resonant-mass detectors have traditionally employed metal bars about a metre long and around a tonne in weight, which makes them sensitive to gravitational waves with frequencies up to about a few kilohertz. However, tiny vibrations that would be induced by gravitational waves are extremely difficult to detect above the thermal noise in the bar.

Dr Maxim Goryachev and Professor Michael Tobar proposed a sensitive detector targeting gravitational radiation in the 1-1000 MHz range. Operating at temperatures as low as 0.01 K above the absolute zero, the device is able to operate at the quantum regime allowing for the lowest possible noise level.

Their device consists of a quartz disc about 2.5 cm in diameter hinged to another piece of quartz and placed in a vacuum chamber. A passing high-frequency gravitational wave would cause the disc to vibrate, setting up standing waves of sound across the 2 mm thickness of the disc. The upper surface of the disc is slightly curved to trap sound quanta (phonons), which improves the signal-to-noise ratio.

The nature of quartz allows the waves’ tiny vibrations to be converted into an electrical signal that is amplified by the extremely low-noise superconducting quantum interference device (SQUID) amplifiers. Writing in the journal Physical Review D, Dr Goryachev and Professor Tobar said their detector would be sensitive to strains in space-time as low as 10^-22 per square root of Hertz, “which in principle can cover the frequency range with multiple (>100) modes with quality factors varying between 10⁶ and 10¹⁰”.

The detector could thus feasibly observe gravitational waves before the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US - an upgrade of two existing LIGO detectors which are searching for gravitational waves. The huge detectors are expected to detect signals between about 0.1-1 kHz from sources such as binary neutron stars or colliding black holes by the end of 2018.

The researchers said their device could detect gravitational waves from candidates such as axions and preons forming tiny stars and black holes, as well as put limits on gravitational radiation from the early universe predicted by some Big Bang theories. They added that their system is “easily scalable into arrays and distributed networks that can also impact the overall sensitivity and introduce coincidence analysis to ensure no false detections”.

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