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

Research output: Contribution to journalArticlepeer-review


  • Yiqiu Ma
  • Belinda Heyun Pang
  • Matthew Evans
  • Chunnong Zhao
  • Jan Harms
  • Roman Schnabel
  • Yanbei Chen

Colleges, School and Institutes

External organisations

  • Theoretical Astrophysics 350-17
  • California Institute of Technology


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.


Original languageEnglish
Pages (from-to)776-780
Number of pages5
JournalNature Physics
Publication statusPublished - 15 May 2017


  • quantum metrology , quantum optics