A nonlinear optical interferometer based on crystal superlattices has been demonstrated for the first time in a cascade of up to five crystals. The enhanced sensitivity due to quantum interference and correlations makes it a promising tool for sensing, imaging, and spectroscopy.
Nonlinear interferometers with correlated photons hold promise to advance optical characterization and metrology techniques by improving their performance and affordability. These interferometers offer subshot noise phase sensitivity and enable measurements in detection-challenging regions using inexpensive and efficient components. The sensitivity of nonlinear 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, experiments with more than two nonlinear elements have not been realized, thus hindering the potential of nonlinear interferometers. Here, we build a nonlinear interferometer with up to five nonlinear elements, referred to as superlattices, in a highly stable and versatile configuration. We study the modification of the interference pattern for different configurations of the superlattices 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.
Nonlinear interferometers with quantum correlated photons have been demonstrated to improve optical characterization and metrology. These interferometers can be used in gas spectroscopy, which is of particular interest for monitoring greenhouse gas emissions, breath analysis and industrial applications. Here, we show that gas spectroscopy can be further enhanced via the deployment of crystal superlattices. This is a cascaded arrangement of nonlinear crystals forming interferometers, allowing the sensitivity to scale with the number of nonlinear elements. In particular, the enhanced sensitivity is observed via the maximum intensity of interference fringes that scales with low concentration of infrared absorbers, while for high concentration the sensitivity is better in interferometric visibility measurements. Thus, a superlattice acts as a versatile gas sensor since it can operate by measuring different observables, which are relevant to practical applications. We believe that our approach offers a compelling path towards further enhancements for quantum metrology and imaging using nonlinear interferometers with correlated photons.
Quantum spectroscopy based on nonlinear interferometers attracts increasing attention due to its unique practical advantages [1]. By tailoring spontaneous parametric down conversion (SPDC) for generation of frequency-correlated photons and their nonlocal quantum interference, it becomes possible to perform sensing and imaging across broad spectral ranges through simple detection of paired photons in the visible [2,3]. It was recently demonstrated that nonlinear integrated waveguides can improve the performance of quantum spectroscopy [4]. However, while fabrication of integrated circuits with multiple waveguides is well established, their applications for quantum spectroscopy remain largely undeveloped.
Abstract Nonlinear interferometers are a ubiquitous tool in quantum photonics. As such, they allow spooky‐like imaging with undetected light. On the one side their working principle is based on the principle of induced coherence, which is deeply rooted in the heart of quantum mechanics. On the other side, they bear the strong potential to serve as new tool for biomedical imaging. In this review, an extensive overview about nonlinear interferometers and their working principle is given. A particular focus is set on their exploitation for quantum imaging and sensing. In addition, related side topics and further application fields as well as perspectives are provided.
Interferometers are highly sensitive to phase differences and are utilized in numerous schemes. Quantum interferometers are able to improve the sensitivity of classical interferometers beyond the shot-noise limit. This is done by employing squeezed states of light and destructive interference of the noise in the system. We developed a quantum SU(1,1) interferometer in the time domain. Our nonlinear quantum interferometer creates interference of the input signals at different times and frequencies. We can control the time and frequency differences for investigating the full temporal and spectral structure of the signal. This quantum interferometer can be utilized for sensing ultrafast phase changes, quantum imaging, temporal mode encoding, and studying the temporal structure of entangled photons.