2 µm Ghost Spectroscopy with an Integrated Silicon Quantum Photonics Source

A ghost spectroscopy measurement with an entangled photon source is demonstrated. The transmission spectrum at the 2 mu$\umu$m absorption peak of gaseous carbon dioxide (CO2) is measured in a highly noisy environment. Despite the noise, a high sensitivity S=(5.7 +/- 0.1)x10-2$S = (5.7\pm 0.1)\times 10<^>{-2}$ (g/l)-1$\mathrm{(g/l)<^>{-1}}$ is obtained, a value that is larger than the one found for a classical spectroscopy measurement performed in the same conditions. The probe photons are time-energy correlated photon pairs generated through intermodal spontaneous four-wave mixing in a silicon waveguide. This observation opens the way to low-cost on-chip MIR sensors insensitive to environmental noise.This paper explores the application to quantum ghost spectroscopy of an integrated silicon photonics source of time-energy correlated photon pairs. Carbon dioxide absorption spectroscopy beyond 2 mu$\umu$m is carried out in low signal-to-noise ratio (SNR) conditions, at room temperature and without the need of monochromators. It reports for better sensitivity and limit-of-detection compared to classical transmission measurements.image