  Stimulated Raman spectroscopy has become a powerful tool to study the
spatiodynamics of molecular bonds with high sensitivity, resolution and speed.
However, sensitivity and speed of state-of-the-art stimulated Raman
spectroscopy are currently limited by the shot-noise of the light beam probing
the Raman process. Here, we demonstrate an enhancement of the sensitivity of
continuous-wave stimulated Raman spectroscopy by reducing the quantum noise of
the probing light below the shot-noise limit by means of amplitude squeezed
states of light. Probing polymer samples with Raman shifts around 2950
$cm^{-1}$ with squeezed states, we demonstrate a quantum-enhancement of the
stimulated Raman signal-to-noise ratio (SNR) of 3.60 dB relative to the
shot-noise limited SNR. Our proof-of-concept demonstration of quantum-enhanced
Raman spectroscopy paves the way for a new generation of Raman microscopes,
where weak Raman transitions can be imaged without the use of markers or an
increase in the total optical power.
