Abstract
The measurement of minuscule forces and displacements with ever greater precision is inhibited by the Heisenberg uncertainty principle, which imposes a limit to the precision with which the position of an object can be measured continuously, known as the standard quantum limit1,2,3,4. When light is used as the probe, the standard quantum limit arises from the balance between the uncertainties of the photon radiation pressure applied to the object and of the photon number in the photoelectric detection. The only way to surpass the standard quantum limit is by introducing correlations between the position/momentum uncertainty of the object and the photon number/phase uncertainty of the light that it reflects5. Here we confirm experimentally the theoretical prediction5 that this type of quantum correlation is naturally produced in the Laser Interferometer Gravitationalwave Observatory (LIGO). We characterize and compare noise spectra taken without squeezing and with squeezed vacuum states injected at varying quadrature angles. After subtracting classical noise, our measurements show that the quantum mechanical uncertainties in the phases of the 200kilowatt laser beams and in the positions of the 40kilogram mirrors of the Advanced LIGO detectors yield a joint quantum uncertainty that is a factor of 1.4 (3 decibels) below the standard quantum limit. We anticipate that the use of quantum correlations will improve not only the observation of gravitational waves, but also more broadly future quantum noiselimited measurements.
Original language  English 

Pages (fromto)  4347 
Number of pages  5 
Journal  Nature 
Volume  583 
Early online date  1 Jul 2020 
DOIs  
Publication status  Published  2 Jul 2020 
Keywords
 RCUK
 STFC
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Yu, H. (Creator), McCuller, L. (Creator), Tse, M. (Creator), Kijbunchoo, N. (Creator), Barsotti, L. (Creator), Mavalvala, N. (Creator), Lundgren, A. (Creator), Mozzon, S. (Creator) & Nuttall, L. (Creator), Springer Nature, 2 Jul 2020
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