Optical spectroscopy and imaging have become indispensable tools in life and material sciences, yet their sensitivity and signal-to-noise ratio are fundamentally restricted by shot noise and photodamage. Quantum light sources, characterized by nonclassical correlations, provide a new route toward overcoming these limitations. This review summarizes recent progress in quantum-enhanced spectroscopy and imaging, focusing on the advantages of entangled and squeezed light.
Entangled-photon light, exploiting strong temporal and spatial correlations between photon pairs, demonstrates outstanding noise resilience in diverse imaging scenarios. It enables correlation imaging, quantum imaging with undetected photons, and ultrafast interferometric measurements, achieving high-contrast, low-illumination imaging even under noisy environments. These techniques are particularly promising for biological samples and weak-signal detection, where classical imaging is limited by background noise and scattering. The combination of entanglement-induced coherence and multiphoton interference further expands quantum imaging to mid-infrared and terahertz spectral domains.
On the other hand, squeezed light enhances detection sensitivity by reducing quantum fluctuations below the standard quantum limit. It has been successfully applied to precision displacement sensing, plasmonic detection, and nonlinear optical microscopy, providing significant signal-to-noise improvement while maintaining compatibility with conventional photodetectors.
Overall, quantum light sources offer unique capabilities for achieving high sensitivity, high contrast, and low damage in optical measurements. The development of entangled and squeezed light enables the transition of quantum imaging from laboratory demonstrations toward practical, real-world applications across precision measurement, microscopy, and spectroscopy.