Terrestrial laser-interferometric gravitational wave detectors, such as LIGO, are the most sensitive displacement sensors ever built. As these instruments push toward greater sensitivity, Newtonian noise (gravity gradient noise) is emerging as a fundamental limit at low frequencies, caused by fluctuations in local mass density, from seismic activity to passing vehicles, exerting tiny gravitational forces on the test masses. This noise couples through gravity itself, so it cannot be shielded against, and measuring it directly is essential to subtracting it from detector data.

At the ANU Centre for Gravitational Astrophysics, we've developed the Torsion Pendulum Dual Oscillator (TorPeDO), a sensor built to measure Newtonian noise directly. It consists of two torsion pendulums in a cross formation, with differential rotation read out via four high-finesse Fabry-Pérot cavities locked using the Pound-Drever-Hall technique. Measuring differential rotation between the pendulums lets TorPeDO sense the local Newtonian noise.

Already operated as a controls prototype, the sensor has demonstrated stable rotation measurements at milli-Hertz frequencies where Newtonian noise dominates. It will next move into high vacuum and onto a seismic isolation chain to reach its noise floor. The platform is also applied to fundamental physics searches, including tests for ultralight dark matter.

This hands-on project spans precision optics, mechanical design, electronics, and control systems — students gain experience with cavity locking, isolation hardware, and characterising a real instrument still being commissioned. Projects suit the applicant's interests.

Get in touch to discuss research topics — see the link below, or visit the Centre for Gravitational Astrophysics website.

mechanics, control theory, optics