Laser Power Stabilization beyond the Shot Noise Limit Using Squeezed Light

High levels of laser power stability are necessary for high precision metrology applications. The classical limit for the achievable power stability is determined by the shot noise of the light used to generate a power control signal. Increasing the power of the detected light reduces the relative shot noise level and allows higher stabilities. However, sufficiently high power is not always available and the detection of high laser powers is challenging. Here, we demonstrate a nonclassical way to improve the achievable power stability without increasing the detected power. By the injection of a squeezed vacuum field of light we improve the classical laser power stability beyond its shot noise limit by ${9.4}_{\ensuremath{-}0.6}^{+0.6}\text{ }\text{ }\mathrm{dB}$ at Fourier frequencies between 5 and 80 kHz. For only $90.6\text{ }\text{ }\ensuremath{\mu}\mathrm{A}$ of detected photocurrent we achieve a relative laser power noise of ${2.0}_{\ensuremath{-}0.1}^{+0.1}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}/\sqrt{\mathrm{Hz}}$. This is the first demonstration of a squeezed light-enhanced laser power stabilization and its performance is equivalent to an almost tenfold increase of detected laser power in a classical scheme. The analysis reveals that the technique presented here has the potential to achieve stability levels of $4.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}/\sqrt{\mathrm{Hz}}$ with 58 mA photocurrent measured on a single photodetector.