Brillouin microscopy is an emerging label-free imaging technique used to assess local viscoelastic properties. Quantum-enhanced stimulated Brillouin scattering is demonstrated using low power continuous-wave lasers at 795 nm. A signal-to-noise ratio enhancement of 3.4 dB is reported by using two-mode intensity-difference squeezed light generated with the four-wave mixing process in atomic rubidium vapor. The low optical power and the excitation wavelengths in the water transparency window have the potential to provide a powerful bio-imaging technique for probing mechanical properties of biological samples prone to phototoxicity and thermal effects. The performance enhancement affordable through the use of quantum light may pave the way for significantly improved sensitivity that cannot be achieved classically. The proposed method for utilizing squeezed light for enhanced stimulated Brillouin scattering can be easily adapted for both spectroscopic and imaging applications in biology.
Brillouin microscopy is an emerging label-free imaging technique used to assess local viscoelastic properties. Quantum-enhanced stimulated Brillouin scattering is demonstrated using low power continuous-wave lasers at 795 nm. A signal-to-noise ratio enhancement of 3.4 dB is reported by using two-mode intensity-difference squeezed light generated with the four-wave mixing process in atomic rubidium vapor. The low optical power and the excitation wavelengths in the water transparency window have the potential to provide a powerful bio-imaging technique for probing mechanical properties of biological samples prone to phototoxicity and thermal effects. The performance enhancement affordable through the use of quantum light may pave the way for significantly improved sensitivity that cannot be achieved classically. The proposed method for utilizing squeezed light for enhanced stimulated Brillouin scattering can be easily adapted for both spectroscopic and imaging applications in biology.
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.
Stimulated Raman scattering (SRS) microscopy is a powerful label-free imaging technique that probes the vibrational response of chemicals with high specificity and sensitivity. High-power, quantum-enhanced SRS microscopes have been recently demonstrated and applied to polymers and biological samples. Quantum correlations, in the form of squeezed light, enable the microscopes to operate below the shot noise limit, enhancing their performance without increasing the illumination intensity. This addresses the signal-to-noise ratio (SNR) and speed constraints introduced by photodamage in shot noise-limited microscopes. Previous microscopes have either used single-beam squeezing, but with insufficient brightness to reach the optimal ratio of pump-to-Stokes intensity for maximum SNR, or have used twin-beam squeezing and suffered a 3 dB noise penalty. Here we report a quantum-enhanced Raman microscope that uses a bright squeezed single-beam, enabling operation at the optimal efficiency of the SRS process. The increase in brightness leads to multimode effects that degrade the squeezing level, which we partially overcome using spatial filtering. We apply our quantum-enhanced SRS microscope to biological samples and demonstrate quantum-enhanced multispectral imaging of living cells. The imaging speed of 100×100 pixels in 18 seconds allows the dynamics of cell organelles to be resolved. The SNR achieved is compatible with video-rate imaging, with the quantum correlations yielding a 20% improvement in imaging speed compared to shot noise-limited operation.
Stimulated Raman scattering (SRS) microscopy has emerged as a powerful technique for probing the spatiotemporal dynamics of molecular bonds with exceptional sensitivity, resolution, and speed. However, classically, its performance remains fundamentally constrained by optical shot noise, which imposes a strict limit on detection sensitivity and speed. Here, we demonstrate a quantum-enhanced SRS microscopy platform that circumvents this barrier by harnessing amplitude-squeezed light. Specifically, we generate a Stokes beam with 5.2dB of amplitude squeezing using traveling-wave optical parametric amplification in second-order nonlinear waveguides, and combine it with a tunable coherent pump to access vibrational modes spanning from 1000 to 3100cm−1. Applied to quantum imaging of metabolites in biological tissue (pork muscle), our quantum-enhanced Raman microscope achieves an average noise suppression of 3.6dB and a 51% enhancement in signal-to-noise ratio (SNR) -- to the best of our knowledge, the largest improvement reported to date in quantum-enhanced SRS microscopy of biological samples.
In optical microscopy, as in any biological measurement performed with light, there is a compromise between increasing power to improve resolution and decreasing power to prevent photodamage to the biological structure. Quantum optics allows this compromise to be overcome, enabling improved precision without increased illumination intensity. This thesis demonstrates, for the first time, absolute quantum advantage in microscopy, with a specific focus on Stimulated Raman Scattering (SRS) microscopy.SRS microscopy is a powerful tool widely used in many fields, especially in biomedical sciences. It uses a two-photon process where the light is downshifted in frequency by being absorbed and subsequently inelastically scattered by the intrinsic molecular vibrations in the sample. Each element or molecule has a different response, allowing selective imaging of biological systems. SRS microscopy is particularly useful because it is label-free (no addition of dyes, beads or any implanted tracer), meaning that imaging contrast is achieved without modification of, or interference with, the specimen. Here I present our newly built state-of-the-art shot-noise limited SRS microscope. I also characterize the Raman microscope, describe the developped imaging system and show SRS spectroscopy and imaging of both polystyrene beads and living yeast cells.The quantisation of light introduces a fundamental uncertainty, or quantum noise, in both the amplitude and phase quadratures of an optical field. A squeezed state of light is a state of the optical field where the uncertainty of one of these quadratures is reduced below the quantum noise. Therefore, it provides an approach to reduce the noise level below this quantum noise limit and consequently increases measured signal-to-noise ratio. Here I describe the concepts involved in this technique and present our newly built light squeezer. I characterize the squeezing and show up to -1.3 dB of noise floor reduction for a 6 picosecond pulsed laser, which is the pulse duration that maximises the Raman interaction.In this thesis we apply squeezed states of light in SRS, developping a quantum-enhanced micro- scope. Our SRS Raman intensity noise is ∆I/I ≈ 10^(−7) and the measured quantum efficiency of the built photodiode is η = 72%. In this proof of principle we show a reduction of the noise floor of at least 13% below the quantum noise limit for Raman imaging of polystyrene beads and living yeast cells. This enhancement allowed us to resolve the cell membrane where with conventional microscope would be unresolvable. It also allowed sub-micron spatial resolution. The improved image contrast and reduced imaging time, while avoiding photodamage in the sample, surpasses the current state-of-the-art Raman microscopes and opens opportunities for new discoveries in biophysics.
Nonlinear optical microscopy techniques have emerged as a set of successful tools for biological imaging. Stimulated emission microscopy belongs to a small subset of pump–probe techniques, which can image non-fluorescent samples without requiring fluorescent labeling. However, its sensitivity has been shown to be ultimately limited by the quantum fluctuations in the probe beam. We propose and experimentally implement sub-shot-noise limited stimulated emission microscopy by preparing the probe pulse in an intensity-squeezed state. This technique paves the way for imaging delicate biological samples that have no detectable fluorescence with sensitivity beyond standard quantum fluctuations.
Nonlinear optical microscopy techniques have emerged as a set of successful tools for biological imaging. Stimulated emission microscopy belongs to a small subset of pump-probe techniques which can image non-fluorescent samples without requiring fluorescent labelling. However, its sensitivity has been shown to be ultimately limited by the quantum fluctuations in the probe beam. We propose and experimentally implement sub-shot-noise limited stimulated emission microscopy by preparing the probe pulse in an intensity-squeezed state. This technique paves the way for imaging delicate biological samples that have no detectable fluorescence with sensitivity beyond standard quantum fluctuations.