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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.

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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 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).

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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.

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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 14, 240–244 (2020).

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