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Nonlinear Interference in Crystal Superlattices

Nonlinear interferometers with correlated photons hold a promise to advance optical characterization and metrology techniques by improving their performance and affordability. Nonlinear interferometers offer the sub-shot noise phase sensitivity and enable measurements in detection-challenging regions using inexpensive and efficient components. The sensitivity of such interferometers, defined by the ability to measure small shifts of interference fringes, can be significantly enhanced by using multiple nonlinear elements, or crystal superlattices. However, to date, the experiments with no more than two nonlinear elements have been realized, thus hindering the potential of nonlinear interferometers. Here, we build a nonlinear interferometer with up to five nonlinear elements in a highly-stable and versatile configuration. We study the modification of the interference pattern in different configurations of the superlattice and perform a proof-of-concept gas sensing experiment with enhanced sensitivity. Our approach offers a viable path towards broader adoption of nonlinear interferometers with correlated photons for imaging, interferometry, and spectroscopy.