Quantum noise-limited displacement sensors such as gravitational wave detectors can be improved by using non-classical light1. This has been achieved in limited bands and in a single quadrature (that is, only one of a pair of conjugate variables) by injecting single-mode squeezed vacuum states2,3. Quantum noise in gravitational wave detectors, however, results from input noise in both quadratures, with the dominant quadrature being a function of Fourier frequency. Broadband reduction of this noise via squeezed light injection then requires a method of rotating this quadrature. This can be accomplished with a low-loss, all-pass optical filter with bandwidth in the low audio frequencies4,5, a substantial technical challenge. We present a proof-of-principle demonstration of a recent proposal6 to use two-mode squeezed vacuum states with Einstein–Podolsky–Rosen (EPR) entanglement, which allows the gravitational detector to simultaneously serve as the optical filter, eliminating the need for a separate apparatus.
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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
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This research was supported by the Australian Research Council (ARC) under the ARC Centre of Excellence for Gravitational Wave Discovery grant number CE170100004. M.J.Y. thanks B. Buchler, G. Mansell and V. Adya for discussions.
The authors declare no competing interests.
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Yap, M.J., Altin, P., McRae, T.G. et al. Generation and control of frequency-dependent squeezing via Einstein–Podolsky–Rosen entanglement. Nat. Photonics 14, 223–226 (2020). https://doi.org/10.1038/s41566-019-0582-4
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