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Demonstrating the velocity response of a table-top EPR speedmeter

S. L. Kranzhoff1,2,*, S. L. Danilishin1,2, S. Steinlechner1,2, M. Vardaro1,2, T. Zhang3, and S. Hild1,2

  • 1Maastricht University, Department of Gravitational Waves and Fundamental Physics, 6200MD Maastricht, the Netherlands
  • 2Nikhef, Science Park 105, 1098 XG Amsterdam, the Netherlands
  • 3Institute for Gravitational Wave Astronomy, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom

  • *Contact author: luise.kranzhoff@ligo.org
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Phys. Rev. D 112, 083054 – Published 23 October, 2025

DOI: https://doi.org/10.1103/r8tx-xd6n

Abstract

The sensitivity of gravitational wave interferometers is fundamentally limited by quantum noise, as dictated by the Heisenberg uncertainty principle, due to their continuous position measurement of the end mirrors. Speedmeter configurations, which measure mirror velocity rather than position, have been proposed as a means to suppress quantum backaction noise, but practical implementations remain at an early stage. In this work, we present a table-top realization of the Einstein-Podolsky-Rosen (EPR) speedmeter concept, employing an optical readout scheme based on two orthogonal polarization modes that probe the interferometer with different effective bandwidths. Using a triangular cavity, we demonstrate that the differential optical response between the linear p- and s-polarized modes exhibits a speedlike frequency dependence: vanishing at DC and increasing linearly with signal frequency, up to the bandwidth of the slower mode. With this we show that an optical system equivalent to the EPR speedmeter indeed performs a velocity readout of the end mirror.

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Phys. Rev. D 112, 083054– Published 23 October, 2025
  • Received 18 August 2025
  • Accepted 23 September 2025
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