Abstract
Stimulated Raman spectroscopy has become a powerful tool to study the spatiodynamics of molecular bonds with high sensitivity, resolution, and speed. However, the sensitivity and speed of state-of-the-art stimulated Raman scattering spectroscopy are currently limited by the shot-noise of the light beam probing the Raman process. Here, we demonstrate in a proof-of-principle experiment 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 c m − 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 continuous-wave Raman spectroscopy paves the way for more elaborate demonstrations using state-of-the-art stimulated Raman scattering microscopes, and thus constitutes the very first step towards 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.
Highlights
Optical quantum sensing exploits the unique quantum correlations of non-classical light to enhance the detection of physical parameters beyond classical means [1,2,3,4,5]
Having verified the C-H Raman transition, in the following, we present the demonstration of quantum-enhanced Stimulated Raman Scattering (SRS) spectroscopy
EXPERIMENTAL RESULTS Figure 3 presents our experimental results for quantum-enhanced SRS spectroscopy
Summary
Optical quantum sensing exploits the unique quantum correlations of non-classical light to enhance the detection of physical parameters beyond classical means [1,2,3,4,5]. Squeezed states of light have, for example, enabled quantum-enhanced measurements of mechanical displacements [5,9], magnetic fields [10,11], viscous elasticity of cells [12], and, most prominently, gravitational waves [13] Another field that could significantly benefit from quantum-enhanced sensing by means of squeezed light—but not yet demonstrated—is Stimulated Raman Scattering (SRS) spectroscopy. SRS spectroscopy is a very powerful technique to perform real-time vibrational imaging of living cells and organisms, and it has provided a deeper understanding of properties of biological systems [14,15,16,17] It is based on the stimulated excitation of a Raman transition of the sample under interrogation, thereby resulting in a measurable stimulated Raman loss and gain of the two input beams. Our measurement method has the potential to enable new measurement regimes of Raman bioimaging that are inaccessible by conventional shot-noise limited Raman spectroscopy
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