Multiple activities have been carried out during this period and in the different work packages in the MIRAQLS program:
WP2: The optimum photon and bi-photon states of light for loss-absorption measurements have been identified, disentangling the classical and quantum contributions to them. An open-source library has been developed to efficiently calculate the properties of non-classical light in propagating nonlinear photonic structures, which has been used to compute the optimal properties of single-temporal mode twin-beam squeezers.
WP3: In the quest for pulsed sources of MIR quantum light, multiple findings can be highlighted: The quantum walk comb laser has been demonstrated, a versatile tool for generating broadband combs across various wavelengths. The first measurement of sub-poissonian shot noise in a quantum cascade detector, and the first observation of high harmonic generation driven by nonclassical light have been reported. A low-cost integrated entangled source have been demonstrated, based on LiNbO3 waveguides. Different material platforms for single-photon emitters have been assessed: isotopically enriched Ge, Ge implanted with radiative defects, and Ge-on-Si heterostructures. On the theory side, new light-matter interaction schemes have been proposed to achieve strong photon correlations in the MIR.
WP4: Much activity has focused on the quantum detection of MIR light using GeSn avalanche photo diodes. Prototypes have been fabricated and characterized, demonstrating high gain, moderate excess noise and record bandwidths. Field resolved detection schemes using LiNbO3 were also explored to indirectly measure MIR radiation through a X(2) non-linear interaction with near-infrared pulses. Calculations proved the feasibility of measuring vacuum fluctuations in these platforms. The work on quantum-enhanced field-resolved detection revealed that sub-cycle analysis of quantum fields exploiting X(2) nonlinearities can enhance the detection of quantum fields thanks to the correlations that emerge between signal and idler fields.
WP5: Multiple approaches for the conception and realization of MIR integration components were explored. On the theory side, inverse design and optimization tools were developed. Low-loss lithium niobate and Ge waveguides were fabricated and characterized, reporting losses below 1 db/cm in the 5-10 micron wavelength range. Joint theoretical-experimental work has been devoted to the design and implementation of optimized MIR resonators. Steps towards the development of optimal spectral and temporal phase modulation strategies in the MIR and the implementation of time and frequency transformations have been undertaken too.
WP6: Advances in the realization of quantum spectroscopy with undetected photons by using SU(1,1) interferometry took place. A firs prototype of the device, based on a second-order dispersion-engineered periodically poled LiNb03 waveguide, was fabricated and characterized. On the theory side, a model for the SU(1,1) interferometer has been developed to predict both spectral and temporal interferograms, also crucial for the interpretation of the measurements to be performed in the next reporting period.
WP7: Intense research in the project has focused on pushing Fourier Transform Infrared Spectroscopy to the quantum regime, developing q-FTIR. The strategies explored consists in using dual-frequency combs and quantum light, still under development. Resonance gradient metasurfaces for the enhancement of FTIR detection in the mid-infrared have been developed too.
WP8: Efforts have devoted to the application of quantum sensing to interferometric precision measurements, particularly to optical coherence tomography (OCT). These benefit from results in other WPs. Recent work has been devoted to finalizing the first setup enabling q-OCT, including tests of interferometric stabilities, and post-selection efficiencies. Theory is also underway, which will allow the assessment of the quantum advantage of this q-OCT.
