Quantum interference with undetected photons for sensing and imaging

Quantum interference with undetected photons has gained significant attention in the past ten years due to its potential to decouple the probing and the detection of an active sensing system. The technique is based on correlated photon pairs: one photon interacts with the analyte, and the signature of the interaction is stored in its correlated counterpart. The probing photon remains undetected, while the other photon is measured. When the photons are highly non-degenerate, the spectral separation of the probing and detected photons offers significant advantages in terms of ease of operation and enhanced sensitivity, enabling more precise measurements and analysis with respect to other sensing techniques. This possibility enables a wide range of applications, particularly in fields such as imaging, spectroscopy, and optical coherence tomography, among others. This thesis describes experiments for imaging and sensing based on undetected photons, both in a free-space optical setup and in an integrated photonic circuit. The free-space configuration was used to perform undetected three-dimensional imaging reconstruction of diffusive targets. This validation of imaging with undetected photons paves the way to further development to in vivo biomedical imaging, covert imaging, and remote sensing. On the other hand, the integrated configuration overcomes the limitation of alignment tolerance and scalability of a free-space optical setup, enabling the development of integrated sensors based on undetected photons.