Broadband reduction of quantum radiation pressure noise via squeezed light injection

The Heisenberg uncertainty principle states that the position of an object cannot be known with infinite precision, as the momentum of the object would then be totally uncertain. This momentum uncertainty then leads to position uncertainty in future measurements. When continuously measuring the position of an object, this quantum effect, known as back-action, limits the achievable precision(1,2). In audio-band, interferometer-type gravitational-wave detectors, this back-action effect manifests as quantum radiation pressure noise (QRPN) and will ultimately (but does not yet) limit sensitivity(3). Here, we present the use of a quantum engineered state of light to directly manipulate this quantum back-action in a system where it dominates the sensitivity in the 10-50kHz range. We observe a reduction of 1.2dB in the quantum back-action noise. This experiment is a crucial step in realizing QRPN reduction for future interferometric gravitational-wave detectors and improving their sensitivity. An amplitude squeezed light source that operates down to 1kHz frequencies-the lowest squeezing frequency-is generated in nonlinear crystal-based systems. By injecting the squeezed light into a microresonator, the quantum radiation pressure noise is reduced by 1.2dB.