The localization of the SERS effect from air nitrogen molecules over nanostructured self-assembled silver films has been experimentally investigated. In our previous experiments on surface-enhanced Raman scattering from myoglobin on such SERS substrates, the intensity of the scattering spectrum depended on the thickness of the analyte. At very low analyte concentrations, giving an estimated monolayer on the substrate, little or no SERS was observed; at higher concentrations, analyte crystallites as thick as 0.5 to 1 mu m gave an intense SERS spectrum. Since the plasmon resonance field of a single nanoparticle is mainly localized near its surface on the scale of a few nanometers, the electromagnetic and chemical mechanisms of SERS are localized at the same distances. We hypothesized that for a rough metal with a developed surface consisting of crystallites of noble metals with subwavelength sizes, the total field of these particles can localize the SERS effect at larger distances from the substrate. While the literature data on this issue for continuous films are contradictory, we present the results of a systematic study of our hypothesis. Experiments with the SERS effect from air nitrogen molecules exclude any volume or chemical effects from the analyte. The measured scale of the long-range SERS contrasts with the traditional idea of the extremely fast attenuation of SERS at distances of units to tens of nanometers. The observed characteristic space scale of similar to 140 nm exceeds the characteristic scales of inhomogeneities in the substrate nanostructure. An explanation of this fact should apparently be sought in terms of the mechanism of excitation, scattering, and localization of hybrid plasmon-polariton waves under conditions of a real optical scheme, taking into account the morphology and structure of silver films. The experimental methods (Z-Scan) used in the work allow measuring the real point distribution function for confocal microscopes.

In this study, we have investigated the surface-enhanced Raman scattering (SERS) spectra of myoglobin on silver substrates with different morphology. The aim was to determine the optimal parameters of analyte and substrate preparation for obtaining of high-amplitude SERS spectra of proteins. It is shown that not only the morphology of the silver film, but also the method of analyte molecules deposition on the SERS substrate plays an important role. Glass substrates were pretreated several stages in organic solvents before silver deposition. It is shown that pretreatment of the glass surfaces lead to a decrease in the silver SERS film roughness. Myoglobin was applied to the SERS substrates in the form of an aqueous solution and then it was precipitated under ultrasonic treatment at frequencies of 580 kHz and 47 kHz. SERS spectra were recorded at randomly selected locations of the dried precipitate using excitation wavelengths of 785 nm and 532 nm. Unusual form myoglobin SERS spectra were observed, in which only certain part of the spectrum demonstrated the additional enhancement in comparison to the overall spectrum. We called such spectra extraordinary ones. In the extraordinary myoglobin SERS spectra, the amplitude of the vibrational band at 996 cm-1 is approximately five times more intense compared to other strong vibrational bands. And the ratio of amplitudes of vibrational band in extraordinary SESR spectra increased by more than an order of magnitude compared to the same ratio for amorphous myoglobin. The article discusses the mechanisms leading to the appearance of extraordinary SERS spectra.

Multilayer nanoscale systems incorporating ultrathin tunnel barriers, magnetic materials, amorphous oxides, and promising dielectrics are essential for next-generation logics, memory, quantum, and neuro-inspired computing. Still, an ultrathin film control at the atomic scale remains challenging. Here, we introduce a complementary metal-oxide semiconductor–compatible approach using focused ion beam irradiation for buried ultrathin films’ engineering with subangstrom thickness control. Molecular dynamics simulations confirm the pivotal role of ion-induced crystal defects. Its performance is exemplified by Josephson junction resistance tuning in the range of 2 to 37% with a 0.86% standard deviation in completed chips. Furthermore, it enables ±17-megahertz frequency accuracy (±0.172 angstrom tunnel barrier thickness variation) in superconducting multiqubit processors, as well as qubit energy relaxation and echo coherence times exceeding 0.5 milliseconds.

High-fidelity two-qubit gates are essential for scalable quantum computing. We present a scheme based on superconducting transmon qubits and a control pulse delivery protocol that enables arbitrary controlled-phase gates modulated solely by an independent arbitrary waveform generator pulse. We combined a tunable coupler design with bipolar flux-pulsing to demonstrate a high-fidelity gate with a performance of 99.5%. Our gates inherit the advantages of both approaches: minimal residual ZZ coupling, built-in echo-like low-frequency noise protection, and time-scale control pulse reproducibility, while remaining easy to calibrate. We optimize the system energy levels to mitigate leakage to the coupler and suppress residual interactions. Numerical simulations of the scheme as three qutrits indicate that an error below 1 × 10^-4 is achievable. We confirm the scalability potential of the proposed scheme on a high-fidelity 4-qubit quantum processor.

In this review, we provide a practical guide on protection of superconducting quantum circuits from broadband electromagnetic and infrared-radiation noise by using cryogenic shielding and filtering of microwave lines. Recently, superconducting multi-qubit processors demonstrated quantum supremacy and quantum error correction below the surface code threshold. However, the decoherence-induced loss of quantum information still remains a challenge for more than 100 qubit quantum computing. Here, we review the key aspects of superconducting quantum circuits protection from stray electromagnetic fields and infrared radiation, namely, multilayer shielding design, materials, filtering of the fridge lines and attenuation, cryogenic setup configurations, and methods for shielding efficiency evaluation developed over the last 10 years. In summary, we make recommendations for creation of an efficient and compact shielding system as well as microwave filtering for a large-scale superconducting quantum systems.

Specific monosaccharide residue, β-D-galactofuranose (Galf) featuring a five-membered ring structure, is found in the glycans of fungi and bacteria, but is normally absent in healthy mammals and humans. In this study, synthetic oligosaccharides mimicking bacterial and fungal glycans were investigated by SERS (Surface-Enhanced Raman Scattering) techniques for the first time to distinguish between different types of glycan chains. SERS spectra of oligosaccharides related to fungal α-(1→2)-mannan, β-(1→3)-glucan, β-(1→6)-glucan, galactomannan of Aspergillus, galactan I of Klebsiella pneumoniae, and diheteroglycan of Enterococcus faecalis were measured. To analyze the spectra, a number of machine learning methods were used that complemented each other: principal component analysis (PCA), confidence interval estimation (CIE), and logistic regression with L1 regularization. Each of the methods has shown own effectiveness in analyzing spectra. Namely, PCA allows the visualization of the divergence of spectra in the principal component space, CIE visualizes the degree of overlap of spectra through confidence interval analysis, and logistic regression allows researchers to build a model for determining the belonging of the analyte to a given class of carbohydrate structures. Additionally, the methods complement each other, allowing the determination of important features representing the main differences in the spectra containing and not containing Galf residue. The developed mathematical models enabled the reliable identification of Galf residues within glycan compositions. Given the high sensitivity of SERS, this spectroscopic technique serves as a promising basis for developing diagnostic test systems aimed at detecting biomarkers of fungal and bacterial infections.

Superconducting single quantum logic integrated circuits traditionally exploit magnetron sputtered niobium thin films on silicon oxide substrates. The sputtering depends on multiple process parameters, which dramatically affect mechanical, electrical, and cryogenic properties of Nb thin films. In this work, we focus on the comprehensive relationship study between 200-nm Nb film characteristics and their intrinsic stress. It is shown that there is a critical value of the working pressure pcritical at the fixed sputtering power above which stress in the film relaxes whereas the film properties degrade significantly. Below pcritical one can control intrinsic stress in the wide range from -400 MPa to +600 MPa maintaining perfect film surface with a 0.8 nm roughness (Rq), electrical resistivity less than 20 uOhm*cm, critical superconducting transition temperature above 8.9 K and residual resistance ratio over 6.4. We suggest a modified kinetic model to predict Nb films stress with the linear dependence of high-energy parameters on the working pressure replaced with an exponential one, which allowed reduction of the approximation error from 20 to 8

The review analyzes recent advances, challenges, and practical applications in the field of enzymes within the framework of chemical enzymology and enzyme engineering. The achievements in the fundamental understanding of molecular mechanisms of the catalytic cycle of enzymatic reactions made using quantum mechanics/molecular mechanics methods with supercomputer technologies and bioinformatic approaches are considered. The design of protein biocatalysts with new properties is a fundamentally significant methodology of the bioengineering approach to solving practical problems, which is demonstrated by a number of examples. The increasing role of biocatalysis in medicine and biomedical research is illustrated by addressing the problems of antibiotic synthesis and overcoming antibiotic resistance of bacteria, mechanisms of neurodegenerative diseases and development of drugs to treat Alzheimer's disease, biocatalytic processes of DNA repair and the role of mechanisms of functioning of heme peroxidases in the human body. The use of enzymes to degrade endogenous and exogenous toxicants has been greatly developed in recent decades. The advances and problems of using enzymes in therapy and drug delivery are analyzed. The fundamental role of enzymes in modern analysis and diagnosis is noted. The review considers a new trend in the development of bioanalytical methods using aptamers, multi-analysis systems on biochips, surface-enhanced Raman scattering systems, and bioelectroanalysis. The bibliography includes 460 references.

Silicon nitride (SiN) is currently the most prominent platform for photonics at visible and near-IR wavelength bandwidth. However, realizing fast electro-optic (EO) modulators, the key components of any integrated optics platform, remains challenging in SiN. Recently, transparent conductive oxides (TCO) have emerged as a promising platform for photonic integrated circuits. Here we make an important step towards exceeding possibilities of both platforms, reporting for the first-time high-speed ITO electro-optic modulators based on silicon nitride waveguides. The insertion losses of 5.7 dB and bandwidth of about 1 GHz are shown for 300 nm-thickness SiN waveguide platform with 9.3-um-length hybrid waveguide. The fabrication process of devices requires only standard clean room tools, is repeatable and compatible with the CMOS technology. Simulation results of optimized device designs indicate that further improvement is possible and offer promising opportunities towards silicon nitride photonic computation platforms based on ITO.

At the present time, ultrahigh performance superconducting nanowire single-photon detectors are the key elements in a variety of devices from biological research to quantum communications and computing. Accurate tuning of superconducting material properties is a powerful resource for fabricating single-photon detectors with desired properties. Here, we report on the major theoretical relations between ultrathin niobium nitride (NbN) film properties and superconducting nanowire single-photon detector characteristics, as well as the dependence of ultrathin NbN film properties on reactive magnetron sputtering recipes. Based on this study, we formulate the exact requirements for ultrathin NbN films for ultrahigh performance superconducting nanowire single-photon detectors. Then, we experimentally studied the properties of ultrathin NbN films (morphology, crystalline structure, critical temperature, and sheet resistance) on silicon, sapphire, silicon dioxide, and silicon nitride substrates sputtered with various recipes. We demonstrate ultrathin NbN films (obtained with more than 100 films deposition) with a wide range of critical temperature from 2.5 to 12.1 K and sheet resistance from 285 to 2000 Ω/sq and report a sheet resistance evolution of more than 40% within two years. Finally, we found out that one should use ultrathin NbN films with a specific critical temperature near 9.5 K and a sheet resistance of about 350 Ω/sq for ultrahigh performance state-of-the-art superconducting nanowire single-photon detectors at 1550 nm wavelength.

Reproducibility of Al/AlOx/Al Josephson junctions is a challenge for scaling up superconducting quantum processors. The frequency uncertainty of the transmon qubits arising from the fabrication process is attributed to deviations in the Josephson junction microstructure and electrical properties. Here, we present a solution for this problem using the post-fabrication Josephson junction thermal annealing process. The developed thermal post-exposure method allows not only to increase the junction resistance by 175%, but also to decrease by 60% with a step of 10% in Rn, which opens up new possibilities for tuning the frequency of qubits. The resistance is shown to be strongly temperature dependent, and is weakly dependent on the holding time. The linear dimensions of the electrodes and the sidewalls contribution to the total JJ area also have a significant impact on the final resistance after annealing. Finally, a theoretical model of the structure modification in a tunnel barrier with changes in oxygen concentration gradient is proposed. The proposed thermal annealing approach can be used to form stable and reproducible tunnel barriers and scalable frequency trimming for widely used fixed-frequency transmon qubits.

Recently, silicon nitride (Si3N4) photonic integrated circuits (PICs) are of a great interest due to their extremely low waveguides losses. The number of Si3N4 integrated photonics platform applications is constantly growing including the Internet of Things (IoT), artificial intelligence (AI), light detection and ranging (LiDAR) devices, hybrid neuromorphic and quantum computing. Their heterogeneous integration with a III-V platform leads to a new advanced large scale PICs with thousands of elements. Here, we review key trends in Si3N4 integrated circuits technology and fill an information gap in the field of state-of-the-art photonic devices operating from visible to mid-infrared spectra. A comprehensive overview of Si3N4 integrared circtuis microfabrication process details (deposition, lithography, etching, etc.) is introduced. Finally, we point out the limits and challenges of silicon nitride photonics performance in an ultrawide range providing routes and prospects for their future scaling and optimization.

Multilayer nanoscale systems incorporating buried ultrathin tunnel oxides, 2D materials, and solid electrolytes are crucial for next-generation logics, memory, quantum and neuro-inspired computing. Still, an ultrathin layer control at angstrom scale is challenging for cutting-edge applications. Here we introduce a scalable approach utilizing focused ion-beam annealing for buried ultrathin oxides engineering with angstrom-scale thickness control. Our molecular dynamics simulations of Ne+ irradiation on Al/a-AlOx/Al structure confirms the pivotal role of ion generated crystal defects. We experimentally demonstrate its performance on Josephson junction tunning in the resistance range of 2 to 37 Moreover, we showcase +-17 MHz frequency control (+-0.172 A tunnel barrier thickness) for superconducting transmon qubits with coherence times up to 500 us, which is promising for useful fault-tolerant quantum computing. This work ensures ultrathin multilayer nanosystems engineering at the ultimate scale by depth-controlled crystal defects generation.

In this work we present developed silicon nitride high confinement thermally- and E/O tuned platform, that shows propagation losses lower than 0.05 dB/cm for 1550 nm wavelength and lower than 0.30 dB/cm for 935 nm wavelength. This results are achieved by material properties optimization and scattering on roughness and stitching errors minimization. We also show here nanophotonic devices fabricated basing on developed technology, automatic fiber coupling and wire bonding.

Lab-on-a-chip (LOC) forms the basis of new-generation portable analytical systems. LOC allows the manipulation of ultralow flows of liquid reagents and multistep reactions on a microfluidic chip, which requires a robust and precise instrument to control the flow of liquids on a chip. However, commercially available flow meters appear to be a standalone option adding a significant dead volume of tubes for connection to the chip. Furthermore, most of them cannot be fabricated within the same technological cycle as microfluidic channels. Here, we report on a membrane-free microfluidic thermal flow sensor (MTFS) that can be integrated into a silicon-glass microfluidic chip with a microchannel topology. We propose a membrane-free design with thin-film thermo-resistive sensitive elements isolated from microfluidic channels and a 4'' wafer silicon-glass fabrication route. It ensures MTFS compatibility with corrosive liquids, which is critically important for biological applications. MTFS design rules for the best sensitivity and measurement range are proposed. A method for automated thermo-resistive sensitive element calibration is described. The device parameters are experimentally tested for hundreds of hours with a reference Coriolis flow sensor demonstrating a relative flow error of less than 5% within the range of 2-30 μL min-1 along with a sub-second time response.

The modifications of the microstructure of myoglobin deposited onto SERS-active Ag-based substrates by drying a drop of aqueous solution with and without laser irradiation and the corresponding surface-enhanced Raman scattering (SERS) spectra are studied. It is shown that drying with laser irradiation leads to the formation of protein aggregates of various types, including crystal-like aggregates. It is also shown that after such drying, the aggregates generally have SERS spectra characterized by a change in the position of the vibration bands and the ratios of their amplitudes compared to the spectra of proteins dried without additional treatment. In particular, parts of the SERS spectra of aggregates formed under laser irradiation are characterized by an additional enhancement (up to 100×) compared to the SERS spectra of myoglobin dried in air at room temperature. The crystallization processes were modeled using the results of atomic force microscopy morphology studies of dried myoglobin on the SERS-active substrates to determine the conditions under which crystal-like aggregates start to grow at surface irregularities, specifically those with a volume close to that of the critical-size nucleus, and where the lowest energy of formation occurs. A correlation is established between surface irregularities, the amplitude, and the change in the SERS spectra during the drying of a myoglobin solution sample on a nanostructured Ag-based surface.

In this work, we show possible ways and give guidelines for silicon nitride photonic integrated circuits fabrication process optimization, suitable for near-IR and telecom bandwidth. Most attention is focused on minimization of scattering losses originating from e-beam lithography and dry etching of silicon nitride.

Low-loss photonic integrated circuits (PICs) are the key elements in future quantum technologies, nonlinear photonics and neural networks. The low-loss photonic circuits technology targeting C-band application is well established across multi-project wafer (MPW) fabs, whereas near-infrared (NIR) PICs suitable for the state-of-the-art single-photon sources are still underdeveloped. Here, we report the labs-scale process optimization and optical characterization of low-loss tunable photonic integrated circuits for single-photon applications. We demonstrate the lowest propagation losses to the date (as low as 0.55 dB/cm at 925 nm wavelength) in single-mode silicon nitride submicron waveguides (220×550 nm). This performance is achieved due to advanced e-beam lithography and inductively coupled plasma reactive ion etching steps which yields waveguides vertical sidewalls with down to 0.85 nm sidewall roughness. These results provide a chip-scale low-loss PIC platform that could be even further improved with high quality SiO2 cladding, chemical-mechanical polishing and multistep annealing for extra-strict single-photon applications.

When talking about nanophotonics, quantum computing and sensing high-quality factor plasmonic devices are playing crucial role. In most cases for making such devices one has to use non-lattice matched or transparent amorphous substrates. Plasmonic devices quality factor is mainly determined by ohmic losses, scattering losses at grain boundaries, and in-plane plasmonic scattering losses of a metal - substrate system. We demonstrate here the e-beam evaporation method to deposit ultralow-loss silver thin films on transparent lattice-mismatched substrates. This process corresponds to evolutionary selection growth mode. The key feature of our approach is a precise control during the whole process consisting of film deposition on a cold substrate, self-crystallization and subsequent annealing for stress relaxation. In particular, the stress relaxation leads to further grains growth. We are able to deposit 100 nm thick polycrystalline silver films with micrometer-scale grains, low roughness and ultralow optical losses. Finally, we show ultrahigh-quality factor plasmonic silver nanostructures on transparent lattice-mismatched substrate. This can be of the great interest for high performance and single-molecule optical sensors applications.