Proposal for gravitational-wave detection beyond the standard quantum limit through EPR entanglement

By Yiqiu Ma, H. Miao, B. Pang, M. Evans, Chunnong Zhao, J. Harms, Roman Schnabel, Yanbei Chen. Nature Physics, 2016

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In continuously monitored systems the standard quantum limit is given by the trade-off between shot noise and back-action noise. In gravitational-wave detectors, such as Advanced LIGO, both contributions can be simultaneously squeezed in a broad frequency band by injecting a spectrum of squeezed vacuum states with a frequency-dependent squeeze angle. This approach requires setting up an additional long baseline, low-loss filter cavity in a vacuum system at the detector’s site. Here, we show that the need for such a filter cavity can be eliminated, by exploiting Einstein–Podolsky–Rosen (EPR)-entangled signals and idler beams. By harnessing their mutual quantum correlations and the difference in the way each beam propagates in the interferometer, we can engineer the input signal beam to have the appropriate frequency-dependent conditional squeezing once the out-going idler beam is detected. Our proposal is appropriate for all future gravitational-wave detectors for achieving sensitivities beyond the standard quantum limit. Quantum metrology can enhance gravitational-wave detection through the use of squeezed states. A new proposal now suggests that with EPR entanglement one can do even better, reaching sensitivities beyond the standard quantum limit.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/d1deaeba7b00f02c1a066f683b29379099b8a96b