Quantum sensing is an emerging field of quantum optics that seeks to take advantage of quantum correlations available in quantum states of light to enable sensitivities beyond the fundamental classical limits. The sensitivity of measurements and sensing apparatus when using classical states of light is limited to the shot-noise limit (SNL), which is achieved with coherent states of light.

Two-mode squeezed states of light (twin beams) have quantum correlations both in time and space, leading to temporal and spatial squeezing properties. Several applications can benefit from such noise reduction to enable new approaches, such as quantum-enhanced interferometry, quantum imaging, and quantum sensing. The emergence of quantum technologies has been referred to as the second quantum revolution. For metrology and sensing applications, in particular, it has led to new state-of-the-art sensitivity limits.

In this thesis, we discuss the implementation of quantum sensing based on squeezed states of light and plasmonic sensors as a platform for the demonstration of real-life quantum sensing. We present a quantum-enhanced plasmonic sensing setup that can detect changes in the refractive index of air beyond the SNL. Furthermore, we generalize such experimental apparatus to probe an array of sensors using the quantum correlations present in different spatial locations to demonstrate a parallel quantum-enhanced plasmonic sensing scheme that can simultaneously detect changes in the refractive index of air in multiple locations with a single probing beam. These results prove the applicability of twin beams for real-life applications based on plasmonic sensors. The spatially resolved sensing scheme can be extended to pixel-size sensing of multiple sensors for multi-parameter estimation and detection applications to reach more complex sensing architectures.