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Extending Ground-Based Gravitational-Wave Sensitivity to 5 Hz

Amit Singh Ubhi1,*, Lari Koponen1, Jiri Smetana1, Yulin Xia2, Haixing Miao2, Emilia Chick1, John Bryant1, Geraint Pratten1, Teng Zhang1 et al.

Richard Mittleman3, Peter Fritschel3, Alan V. Cumming4, Giles Hammond4, and Denis Martynov1

  • *Contact author: a.s.ubhi@bham.ac.uk
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Phys. Rev. Lett. 137, 031401 – Published 16 July, 2026

DOI: https://doi.org/10.1103/65gz-dcjz

Abstract

Extending the sensitivity of terrestrial gravitational-wave detectors below 20 Hz is a long-standing challenge, limited by ground motion and inertial sensing noise. In this Letter, we demonstrate ultra-high-vacuum compatible inertial isolation and position sensing technologies that achieve active platform stabilization down to 10 mHz. Our laser position sensors reach a sub−pm/Hz sensitivity above 10 mHz, independent of the input light polarization, representing a 100-fold improvement over the current LIGO position sensors. In addition, our inertial sensors provide at least a factor of 5 improvement in low-frequency sensitivity compared to state-of-the-art commercial seismometers. We integrate these technologies into a LIGO-like interferometer model and predict a low-frequency sensitivity improvement of up to an order of magnitude at 10 Hz, with enhanced linearity and calibration stability. This extension increases the detection horizon for intermediate-mass black hole binaries of mass 103M⊙ by a factor of 3 and increases the SNR for all lower mass binaries. Our results provide the first experimental demonstration of a practical pathway to sub-10 Hz operation of terrestrial gravitational-wave detectors and establish key technologies for next-generation observatories such as Cosmic Explorer and Einstein Telescope.

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Phys. Rev. Lett. 137, 031401– Published 16 July, 2026
  • Received 2 March 2026
  • Accepted 10 June 2026
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