Superconducting quantum circuits are one of the leading quantum computing platforms. To advance superconducting quantum computing to a point of practical importance, it is critical to identify and address material imperfections that lead to decoherence. In this talk, I will show how terahertz Scanning Near-field Optical Microscopy (SNOM) can be used to probe functional devices such as coplanar microwave resonators and inform the processing of new materials for quantum technology.
In this article, we report our work on the development of a non- invasive, rapid, robust, and high-fidelity technique that can be used to discriminate between genetic variants. Our study focused on terahertz (THz) spectroscopy and imaging to distinguish between genetic variants of the Allium genus rapidly and accurately. This was done by measuring the cellular water dynamics of the samples by measuring their evaporation profiles using Laser Feedback Interferometry (LFI) with THz Quantum Cascade Lasers (QCL). The evaporation profiles of the samples were then processed to create trajectories in the amplitude-phase domain, which correlated with cell age, cell type, and the amount of water bound to biomolecules. This technique can differentiate between the members of the Allium genus. The presence of outliers was also studied to determine the effectiveness of the technique for different samples and to negate external influence. This was done to discern the extent of influence of cell biomechanics and biochemistry between genetic variants. We found that within a genus, different species would have different degree of interaction between cellular water and cell biochemistry, which could be clearly mapped out using THz-QCL-based LFI. Based on our observations, we propose that this method could be appropriate for observing minute alterations in cellular water dynamics in real-time, and in the future, has the potential to be employed for rapid and effective genetic discrimination in agricultural and genome conservation applications.
Taj Mahal, made of exquisite white calcite, continues to deteriorate due to the emission of sulphur dioxide, methane etc. by industries and vehicular exhaust caused by the dense population in the region. Our previous collaborative works on samples with Pietra-Dura works already showed damages and irregularities including surface discolouration due to methane, water inclusions in the volume, and sub-surface cracks employing micro-Raman spectroscopy, broadband Terahertz Time Domain Imaging (THz-TDI) and THz Laser Feedback Interferometry (THz-LFI). Here, two types of samples having similar artwork, but one made of marble having high sulphur content have been investigated. Employing energy dispersive X-Ray analysis (EDAX), the sulphur content in the previous calcite sample is found to be nil while the new one has 16% by weight. While visually the samples are similar, under optical and scanning electron microscopy (SEM), calcite presents grainier structure with larger porosity while the other one appears denser with finer porosity. In ultra-low-frequency (ULF) Raman spectroscopy, the calcite sample (less than 0.15% Mg content) produces a significant line at 1100 cm-1 while the marble with sulphur shows a markedly different spectral response with the significant line at 1010 cm-1 . Using both THz-TDI and THz Continues Wave (THz CW) imaging, we concluded that calcite marble has significantly larger THz penetration even at 1 THz, while the marble with high sulphur content has very low THz penetration even below 0.5 THz and high THz absorption offering higher THz reflectivity. These observations pave the way to objectively detect the extent of environmental damage to marble structures across the globe.
Measuring polarisation, spectrum, temporal dynamics, and spatial complex amplitude of optical beams is essential to studying phenomena in laser dynamics, telecommunications and nonlinear optics. Here, we harness principles of spatial state tomography to measure a complete description of an unknown beam as a set of spectrally, temporally, and polarisation resolved spatial state density matrices. Each density matrix slice resolves the spatial complex amplitude of multiple mutually incoherent fields, which over several slices reveals the spectral or temporal evolution of these fields even in scenarios when they spectrally or temporally overlap. We demonstrate these features by characterising the rich spatiotemporal and spatiospectral output of a vertical-cavity surface-emitting laser.
Paper, as a hygroscopic dielectric material, does not have specific spectral signatures in the Terahertz (THz) range from 0.2-6 THz. However, because of its constituent materials, including dry matter, moisture, and air pockets, it absorbs THz radiation, similar to biological tissues and green leaf. Though the absorption loss is not significant, varying levels of dampness in wet paper are observed over time using continuous wave (CW) based THz Spectroscopic system to quantify the moisture content of wet paper relative to paper at ambient environment. For this purpose, effective medium theory (EMT) approaches including Bruggeman (BM), Landau–Lifshitz–Looyenga (LLL), and Complex Refractive Index (CRI) models are analysed. However, EMT models are dependent on physical and optical properties of paper and water, which are not well-defined and are dependent on assumptions, approximations and rigorous calculations. To remove such dependencies, supervised machine learning regression (SMLR) algorithms in the form of decision tree (DT), random forest (RF), and support vector regression (SVR) are investigated. The conditioning of the training parameters is dependent on spectroscopic data which reduces the processing time and improves efficiency due to elimination of approximations. Prediction efficiency of SMLR models is observed to be better than that of EMT models. RF shows the best results in terms of coefficient of determination, 𝑅2 but the time required for training is more when compared to DT and SVR models. DT models show consistent performance, while predictions using different SVR models show variance with 𝑅2 ranging from 0.42 to 0.98.
This present collaborative research, undertaken in two different hemispheres, in an effort to address the challenge of early structural and sub-surface assessment of heritage marble architectures, like the Taj Mahal, using two complementary non-contact, non-invasive imaging techniques in the THz spectral range. In our previous work, it was already demonstrated that the complementary techniques of broadband Terahertz Time Domain Imaging (THz-TDI) and microRaman spectroscopy are successful in probing volume and surface damage in marble with Pietra-dura work. In the present work, the unique combination of THz-TDI and highly sensitive THz-Laser Feedback Interferometry (THz-LFI) have been explored to study sub-surface damage and irregularities of marble structures with Pietra-dura motif. These optical techniques hold immense possibility in large-scale architectural restoration projects as they collectively provide accurate structural depth profile up to several inches into the volume of the marble including the strain generated within the structure leading to potential cracks.
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