Quantum-correlated mid-infrared absorption spectroscopy with superconducting nanowire single-photon detectors

Mid-infrared (MIR) spectroscopy serves as a powerful tool for molecular structure identification and chemical composition analysis. However, conventional Fourier-transform infrared spectrometers (FTIR) demonstrate compromised signal-to-noise ratios (SNR) under low-light conditions, which severely limit their performance in high-sensitivity applications. Although MIR superconducting nanowire single-photon detectors (SNSPDs) offer high detection efficiency and low timing jitter, their performance is hindered by background dark counts caused by room-temperature blackbody radiation. In this work, we present a quantum-correlated absorption spectroscopy platform that combines MIR-SNSPDs with entangled photon pairs to overcome these limitations. Leveraging the intrinsic temporal and spectral correlations of the photon pairs, coincidence detection effectively distinguishes signal photons from dominant thermal noise, achieving a remarkable improvement of two orders of magnitude in SNR under ultralow pump power conditions. The system achieves a spectral coverage of 3350-3540 nm with a resolution of 3.7 cm^-1 at 3.4 µm, operating at an ultralow illumination photon flux of 4.4 × 10⁶ photons/s. Validation experiments using polystyrene and polyethylene samples successfully detected CH₂ vibrational modes, demonstrating the platform's capability for ultrasensitive biochemical analysis and material characterization. By integrating quantum correlation with MIR-SNSPDs, this work establishes a new paradigm for high-performance MIR spectroscopy in low-light scenarios.