Demonstration of interferometer enhancement through Einstein–Podolsky–Rosen entanglement


The recent series of gravitational-wave detections by the Advanced LIGO and Advanced Virgo observatories have launched the new field of gravitational-wave astronomy. As the sensitivity of gravitational-wave detectors is limited by the quantum noise of light, concepts from quantum metrology have been adapted to increase the observational range. Since 2010, squeezed light with reduced quantum noise has been used to achieve improved sensitivity at signal frequencies above 100 Hz. However, 100-m-long optical filter resonators would be required to also improve the sensitivity at lower frequencies, adding significant cost and complexity. Here, we report a proof-of-principle set-up of an alternative concept that achieves the broadband noise reduction by using Einstein–Podolsky–Rosen entangled states instead. We show that the desired sensitivity improvement can then be obtained with the signal recycling resonator that is already part of current observatories, providing a viable alternative to high-cost filter cavities.

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Fig. 1: Simulation of the improvement in readout quantum noise of a typical laser interferometer with squeezed light for gravitational-wave detection.
Fig. 2: Simplified representation of this work’s experimental set-up.
Fig. 3: Schematics showing the relative positions of signal and idler bands around ωI and ωS and demonstration of frequency-dependent squeeze angle rotation.
Fig. 4: Results of an additional experimental step demonstrating the flexibility of the set-up.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


  1. 1.

    Abernathy, M. et al. Einstein Gravitational Wave Telescope Conceptual Design Study Technical Report ET-0106C-10 (European Gravitational Observatory, 2011);

  2. 2.

    Lantz, B. et al. Instrument Science White Paper 2018 Technical Note LIGO-T1800133-v3 (LIGO Document Control Center, 2018);

  3. 3.

    Abbott, B. P. et al. Exploring the sensitivity of next generation gravitational wave detectors. Classical Quantum Gravity 34, 044001 (2017).

  4. 4.

    Chan, M. L., Messenger, C., Heng, I. S. & Hendry, M. Binary neutron star mergers and third generation detectors: localization and early warning. Phys. Rev. D 97, 123014 (2018).

  5. 5.

    LIGO Scientific Collaboration and Virgo Collaboration. GW170817: observation of gravitational waves from a binary neutron star inspiral. Phys. Rev. Lett. 119, 161101 (2017).

  6. 6.

    Walls, D. F. Squeezed states of light. Nature 306, 141–146 (1983).

  7. 7.

    Breitenbach, G., Schiller, S. & Mlynek, J. Measurement of the quantum states of squeezed light. Nature 387, 471–475 (1997).

  8. 8.

    Schnabel, R. Squeezed states of light and their applications in laser interferometers. Phys. Rep. 684, 1–51 (2017).

  9. 9.

    Caves, C. M. Quantum-mechanical noise in an interferometer. Phys. Rev. D 23, 1693–1708 (1981).

  10. 10.

    Schnabel, R., Mavalvala, N., McClelland, D. E. & Lam, P. K. Quantum metrology for gravitational wave astronomy. Nat. Commun. 1, 121 (2010).

  11. 11.

    McClelland, D. E., Mavalvala, N., Chen, Y. & Schnabel, R. Advanced interferometry, quantum optics and optomechanics in gravitational wave detectors. Laser Photon. Rev. 5, 677–696 (2011).

  12. 12.

    The LIGO Scientific Collaboration. A gravitational wave observatory operating beyond the quantum shot-noise limit. Nat. Phys. 7, 962–965 (2011).

  13. 13.

    The LIGO Scientific Collaboration. Enhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light. Nat. Photon. 7, 613–619 (2013).

  14. 14.

    Grote, H. et al. First long-term application of squeezed states of light in a gravitational-wave observatory. Phys. Rev. Lett. 110, 181101 (2013).

  15. 15.

    Jaekel, M. T. & Reynaud, S. Quantum limits in interferometric measurements. Europhys. Lett. 13, 301 (1990).

  16. 16.

    Danilishin, S. L. & Khalili, F. Y. Quantum measurement theory in gravitational-wave detectors. Rev. Relat. 15, 5–147 (2012).

  17. 17.

    Kimble, H. J., Levin, Y., Matsko, A. B., Thorne, K. S. & Vyatchanin, S. P. Conversion of conventional gravitational-wave interferometers into quantum nondemolition interferometers by modifying their input and/or output optics. Phys. Rev. D 65, 022002 (2001).

  18. 18.

    Chelkowski, S. et al. Experimental characterization of frequency-dependent squeezed light. Phys. Rev. A 71, 013806 (2005).

  19. 19.

    Khalili, F. Y. Optimal configurations of filter cavity in future gravitational-wave detectors. Phys. Rev. D 81, 122002 (2010).

  20. 20.

    Barsotti, L., Harms, J. & Schnabel, R. Squeezed vacuum states of light for gravitational wave detectors. Rep. Prog. Phys. 82, 016905 (2018).

  21. 21.

    Ma, Y. et al. Proposal for gravitational-wave detection beyond the standard quantum limit through EPR entanglement. Nat. Phys. 13, 776–780 (2017).

  22. 22.

    Einstein, A., Podolsky, B. & Rosen, N. Can quantum-mechanical description of physical reality be considered complete? Phys. Rev. 47, 777–780 (1935).

  23. 23.

    Reid, M. D. Demonstration of the Einstein–Podolsky–Rosen paradox using nondegenerate parametric amplification. Phys. Rev. A 40, 913–923 (1989).

  24. 24.

    Bowen, W. P., Schnabel, R., Lam, P. K. & Ralph, T. C. Experimental characterization of continuous-variable entanglement. Phys. Rev. A 69, 012304 (2005).

  25. 25.

    Schori, C., Sørensen, J. L. & Polzik, E. S. Narrow-band frequency tunable light source of continuous quadrature entanglement. Phys. Rev. A 66, 033802 (2002).

  26. 26.

    Hage, B., Samblowski, A. & Schnabel, R. Towards Einstein–Podolsky–Rosen quantum channel multiplexing. Phys. Rev. A 81, 062301 (2010).

  27. 27.

    Brown, D. D. et al. Broadband sensitivity enhancement of detuned dual-recycled michelson interferometers with EPR entanglement. Phys. Rev. D 96, 062003 (2017).

  28. 28.

    Marino, A. M., Stroud, C. R. Jr, Bennink, R. S. & Boyd, R. W. Bichromatic local oscillator for detection of two-mode squeezed states of light. J. Opt. Soc. Am. 24, 335–339 (2007).

  29. 29.

    Li, W., Jin, Y., Yu, X. & Zhang, J. Enhanced detection of a low-frequency signal by using broad squeezed light and a bichromatic local oscillator. Phys. Rev. A 96, 023808 (2017).

  30. 30.

    Beckey, J. L., Ma, Y., Boyer, V. & Miao, H. Broadband quantum noise reduction in future long baseline gravitational-wave detectors via EPR entanglement. Phys. Rev. D 100, 083011 (2019).

  31. 31.

    Yap, M. J. et al. Generation and control of frequency-dependent squeezing via Einstein–Podolsky–Rosen entanglement. Nat. Photon. (2020).

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This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, SCHN 757/6-1), supported by the DFG under Germany’s Excellence Strategy EXC 2121 (‘Quantum Universe’, 390833306) and by the European Research Council (ERC) Project ‘MassQ’ (grant no. 339897).

Author information

J.S., S.S. and R.S. planned the experiment. J.S. and S.S. built and performed the experiment. M.K. provided the theoretical analysis. All authors prepared the manuscript.

Correspondence to Roman Schnabel.

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Südbeck, J., Steinlechner, S., Korobko, M. et al. Demonstration of interferometer enhancement through Einstein–Podolsky–Rosen entanglement. Nat. Photonics (2020).

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