Quantum Fourier Transform Infrared Spectroscopy: Evaluation, Benchmarking, and Prospects.

Sensing with undetected photons has enabled new, unconventional approaches to Fourier transform infrared spectroscopy (FT-IR). Leveraging properties of non-degenerate entangled photon pairs, mid-infrared (mid-IR) information can be accessed in the near-infrared (near-IR) spectral domain to perform mid-IR spectroscopy with silicon-based detection schemes. Here, we address practical aspects of vibrational spectroscopy with undetected photons using a quantum FT-IR (QFT-IR) implementation. The system operates in the spectral range from around 3000 cm^-1 to 2380 cm^-1 (detection at around 12 500 cm^-1) and possesses only 68 pW of mid-IR probing power for spectroscopic measurements with a power-dependence of the signal-to-noise ratio of 1.5 × 10⁵ mW^-1/2. We evaluate the system's short- and long-term stability and experimentally compare it to a commercial FT-IR instrument using Allan-Werle plots to benchmark our QFT-IR implementation's overall performance and stability. In addition, comparative qualitative spectroscopic measurements of polymer thin films are performed using the QFT-IR spectrometer and a commercial FT-IR with identical resolution and integration times. Our results show under which conditions QFT-IR can practically be competitive or potentially outperform conventional FT-IR technology.