During the whole project the following activities have been carried out. Main results are also listed.
QCL-combs optimized for high nonlinearity and broad gain spectrum have been designed at a wavelength of 4.5 μm and 8 μm. An open-source code for dynamic QCL simulations including noise has been developed. It's very important in the context of nonclassical light generation.
Regarding the fermionic analog simulator, a large spacing 1D optical lattice has been realized. It is used to mimic the multi-well configuration of QCL heterostructures. Arbitrary repulsive disordered patterns have also been produced by using a digital micro-mirror device (DMD). Such a disordered potential well mimics localized impurities or grains present in real QCL heterostructures. We have started to study the dynamics of non-interacting homogeneous fermions in 2D disorder landscapes. The first signatures of localization phenomena recently appeared, for critical values of disorder parameters. Regarding the bosonic analog simulator, we have developed an interferometric protocol which, out of a single Bose-Einstein condensate, produces, separates and recombines multiple copies thereof. A multimode Kapitza-Dirac beam-splitter (KDBS) has been realized by exposing the matter wave coherent source, i.e. a Bose-Einstein condensate (BEC) of 87Rb atoms, to a time-pulsed optical lattice. For reducing the amplitude of oscillations in the trap we decided to shift to a "Bragg interferometer", where only two momentum components are present. We found that interatomic interactions affect the fringe wave vectors k, both for the free-space and the in-trap Bragg interferometers.
New fabrication procedures have been developed and implemented in new devices. The QCL-combs bandwidth has been enhanced by strong RF injection of the laser. Thanks to this RF-injection enhancement, together with an external pulse compression, ultra-short pulses have been achieved reaching the ps pulse-width regime and peak powers of a few watts. Dense QCL-combs with relatively low current have been achieved by the combination of active and passive laser sections, and soliton formation has been observed for the first time in a QCL laser ring, which can be relevant to achieve battery-driven spectrometers. Harmonic combs have also been developed and delivered to project partners to perform quantum-based measurements.
An innovative technique for frequency combs characterization based on the dual-comb multiheterodyne detection and the Fourier transform analysis has been developed and applied for characterizing the devices. The analyses proved that the newly-fabricated devices are characterized by a high degree of phase coherence and a well-defined phase relation. The quest for nonclassical features (squeezing) in the new QCLs emission also started. The investigation was carried out in harmonic QCL-combs emission, where only three intense modes are present. A high degree of correlation has been found in the intensity of the two side modes as expected in a generation governed by four-wave mixing. On the other hand, a residual significant amount of uncorrelated noise has been found, preventing us to reach the shot-noise level and unveil possible non-classical correlations in the emission.
High performance QCL combs at a wavelength of 5.3 µm based on a novel low dispersion waveguide design were developed by Alpes Lasers. High performance QCL combs at ~6 µm were also developed. The lasers were integrated in IRsweep’s IRis-F1 dual-comb spectrometer and operated with the new-generation ultra-low noise current drivers developed by ppqSense. Thales implemented coherent detection schemes for LIDAR applications using 2 QCL-combs produced by Alpes Lasers and operated by ppqSense’s QubeCL current drivers and estimated the source-limited performances of dual-comb LiDAR systems. ASI employed a WGMR in order to stabilize a QCL frequency comb. The results open the way to realise an extremely compact, fully-stabilised and narrow-linewidth QCL-comb. A new generation of mid-infrared (MIR) frequency combs using difference frequency generation (DFG) was developed by Menlo Systems. Finally, a market study was performed to evaluate the commercial potential of the frequency comb technology developed in the project and a business plan was prepared accordingly.
Regarding the dissemination activity, we highlight the realization of the project website www.qombs-project.eu the publication of 42+ peer-reviewed papers (+ or in press) in high-impact international journals reporting results related to the Qombs Project, the participation of people involved in the project to numerous international conferences, the organization of an international conference on QCLs (IQCLSW) and the organization of the Qombs Project Final Workshop, and the organization of dissemination activities dedicated to a non-specialized public.
