Spectroscopy in the mid-infrared region is an indispensable tool for identifying molecular types in various fields, including physics, chemistry, and medical sciences. However, conventional infrared light sources, detectors, and noise from blackbody radiation have been the obstacles to miniaturization and higher sensitivity of infrared spectrometers. Quantum infrared spectroscopy, which uses visible and infrared photon pairs in a quantum entangled state, has attracted attention as a new sensing technology that enables infrared spectroscopy with detectors in the visible range. However, the bandwidth of conventional quantum entangled light sources is at most 1 µm or less, which hinders broadband measurements, which are important in spectroscopic applications. Here we have realized an ultra-broadband entangled state of visible–infrared photons with wavelengths from 2 to 5 µm, harnessing a specially designed nonlinear crystal with chirped poling structure inside. Furthermore, we constructed a nonlinear quantum interferometer using the ultra-broadband quantum entangled photons and realized broadband infrared spectroscopy of inorganic and organic materials using a visible detector made of silicon. Our results show that quantum infrared spectroscopy can achieve ultra-broadband spectroscopic measurements and pave the way for the highly sensitive, ultra-compact infrared spectrometers using quantum entangled photons.

中文翻译：

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超宽带量子红外光谱

中红外区域的光谱学是物理、化学和医学等各个领域识别分子类型不可或缺的工具。然而，传统的红外光源、探测器和黑体辐射噪声一直是红外光谱仪小型化和更高灵敏度的障碍。量子红外光谱利用量子纠缠态的可见光和红外光子对，作为一种新的传感技术而引起了人们的关注，该技术可以在可见光范围内使用探测器进行红外光谱分析。然而，传统量子纠缠光源的带宽最多为 1 µm 或更小，这阻碍了宽带测量，而宽带测量在光谱应用中非常重要。在这里，我们利用特殊设计的内部具有啁啾极化结构的非线性晶体，实现了波长为 2 至 5 µm 的可见光-红外光子的超宽带纠缠态。此外，我们利用超宽带量子纠缠光子构建了非线性量子干涉仪，并利用硅制成的可见探测器实现了无机和有机材料的宽带红外光谱。我们的研究结果表明，量子红外光谱可以实现超宽带光谱测量，并为使用量子纠缠光子的高灵敏度、超紧凑红外光谱仪铺平了道路。