Chip-scale quantum light infrared emitters

The mid-infrared (MIR) part of the electromagnetic spectrum is known as the molecular fingerprint region due to the abundance of fundamental rovibrational molecular absorption lines falling therein. Consequentially, this region has been deeply investigated for molecular spectroscopy and sensing applications. One of the most recent scientific and technological breakthroughs in these fields is the development and demonstration of quantum cascade lasers (QCLs) both as MIR compact laser sources and, more recently, as direct frequency-comb emitters. Despite the importance of the MIR spectral region and the large number of applications, lasers, materials, and related technologies are still under development and far less available if compared to the visible and telecom spectral regions. This gap is even more dramatic if we move to the quantum world, as the MIR region nowadays lacks both non-classical light sources and suitable detectors for their investigation. This thesis, entitled Chip-scale quantum light infrared emitters, represents one of the first scientific attempts to push MIR research towards quantum technologies. This manuscript provides a collection of three main experiments which I directly carried out during my Ph.D. research activity. The first experiment regards the realization of a MIR shot-noise-limited balanced detector as a tool for quantum measurements in this spectral region. The second experimental work describes, instead, the measurements of intensity correlations between pairs of modes in MIR QCL frequency combs. Its main results demonstrate the presence of sideband-sideband intensity correlations, as well as sideband-pump correlations, when a MIR QCL is operated in a three-mode harmonic-comb emission, consisting of a bright central mode (the pump) and two weak sidebands. Finally, the third work discussed in this thesis is related to the experimental activity in which I participated during my Ph.D. research period abroad at the Institut de Physique de Nice (France). The specific tasks of this work were the generation, manipulation and detection of small-amplitude Schrödinger’s cat states (the so-called kitten states) at telecom wavelengths. This experience, in particular, gave me the possibility to acquire the skills necessary to handle squeezed and quantum states of light generated by passive media. This gained knowledge will enable me to create, in the near future, a controlled passive system capable of producing MIR non-classical states of light, which can be used as a helpful benchmark for improving the detection setups I developed. In conclusion, the experiments I performed within my Ph.D., which are presented in this manuscript, are aimed at investigating infrared non-classical states of light and at developing suitable detection systems. This paves the way to a very ambitious long-term goal: the realization of the very first chip-scale quantum source based on quantum cascade laser frequency combs.