The goal of this International Roadmap for Devices and Systems (IRDS) chapter is to survey, catalog, and assess the status of technologies in the areas of cryogenic electronics and quantum information processing. Application drivers are identified for sufficiently developed technologies and application needs are mapped as a function of time against projected capabilities to identify challenges requiring research and development effort. Cryogenic electronics (also referred to as low-temperature electronics or cold electronics) is defined by operation at cryogenic temperatures (below −150 °C or 123.15 K) and includes devices and circuits made from a variety of materials including insulators, conductors, semiconductors, superconductors, or topological materials. Existing and emerging applications are driving development of novel cryogenic electronic technologies. Information processing refers to the input, transmission, storage, manipulation or processing, and output of data. Information processing systems to accomplish a specific function, in general, require several different interactive layers of technology. A top-down list of these layers begins with the required application or system function, leading to system architecture, micro- or nano-architecture, circuits, devices, and materials. A fundamental unit of information (e.g., a bit) is represented by a computational state variable, for example, the position of a bead in the ancient abacus calculator or the voltage (or charge) state of a node capacitance in CMOS logic. A binary computational state variable serves as the foundation for von Neumann computational system architectures that dominated conventional computing. Quantum information processing is different in that it uses qubits, two-state quantum-mechanical systems that can be in coherent superpositions of both states at the same time, which can have computational advantages. Measurement of a qubit in a given basis causes it to collapse to one of the basis states. Technology categories covered in this report include: • Superconductor electronics (SCE) • Cryogenic semiconductor electronics (Cryo-Semi) • Quantum information processing (QIP)
Continuing miniaturization of electronic devices, together with the quickly growing number of nanotechnological applications, demands a profound understanding of the underlying physics. Most of the fundamental problems of modern condensed matter physics involve various aspects of quantum transport and fluctuation phenomena at the nanoscale. In nanostructures, electrons are usually confined to a limited volume and interact with each other and lattice ions, simultaneously suffering multiple scattering events on impurities, barriers, surface imperfections, and other defects. Electron interaction with other degrees of freedom generally yields two major consequences, quantum dissipation and quantum decoherence. In other words, electrons can lose their energy and ability for quantum interference even at very low temperatures. These two different, but related, processes are at the heart of all quantum phenomena discussed in this book.This book presents copious details to facilitate the understanding of the basic physics behind a result and the learning to technically reproduce the result without delving into extra literature. The book subtly balances the description of theoretical methods and techniques and the display of the rich landscape of the physical phenomena that can be accessed by these methods. It is useful for a broad readership ranging from master's and PhD students to postdocs and senior researchers.
The materials of The International Scientific – Practical Conference is presented below.
The Conference reflects the modern state of innovation in education, science, industry and social-economic sphere, from the standpoint of introducing new information technologies.
It is interesting for a wide range of researchers, teachers, graduate students and professionals in the field of innovation and information technologies.
Hybrid membranes were prepared by incorporating silica with propyl-imidazoline groups in polybenzimidazoles (phthalide-containing PBI or PBI based on 2,6- or 2,5-pyridinedicarboxylic acids). The influence effects of the silica precursor hydrolysis conditions on the conductivity of the hybrid membranes are studied. Ionic conductivity, water uptake, phosphoric acid doping, and gas permeability of the obtained materials were found to depend on the preparation method and the silica loading. The materials with 10 wt% of functionalized silica present the highest conductivity. A decrease of hydrogen permeability is observed for low silica loadings.
Magnetic nanocomposites involving tetraborate ion (TB)-intercalated Mg–Al-layered double hydroxide (LDH) shell supported on magnesium ferrite core particles are synthesized, characterized, and compared with their non-magnetic analogues. The compositions of the obtained nanocomposites were determined and structural investigations were made by powder X-ray diffraction and Fourier transform infrared spectroscopy. Particle characteristics were examined by size distribution, specific surface area measurements, scanning electron microscopy and transmission electron microscopy. Room-temperature magnetic measurements were performed with a vibrating sample magnetometer. The dynamics and structure of the interlayer water molecules and borate ions were studied by molecular dynamics simulations. Analytical and modeling studies verified that the TB ions were arranged between the LDH layers in oblique positions. The products were found to carry ca. 6% boron (10**17 B atom/μg nanocomposite). The magnetic nanocomposite showed superparamagnetic properties and can potentially find applications in biomedical fields for the site-specific delivery of bio-potent boron agents.
The siloxane surface of uncharged clays is known to be hydrophobic, which is supported by strong experimental and theoretical evidence. For the siloxane surface of charged clays, like smectites, the picture is not as clear. We are aiming to clarify this issue by molecular simulations in which smectite surface hydrophobicity is quantified through the separate contribution of the surface itself, and the contribution due to the presence of charge-balancing cations on the surface. In order to explore systematically the effects of the total smectite charge and its distribution in the structure, a series of molecular dynamics (MD) simulations was performed for several models of dioctahedral smectites and compared with the results for uncharged pyrophyllite.
The largest difference between the simulation results for smectite models with naturally present surface counterions and the models where these ions were artificially removed from the surface, while maintaining the same total charge balance of the model, is in the shape of the water coverage. In the former case, full surface wetting is observed and a relatively flat water film is forming on the surface. Its irregularity and thickness is connected with number of ions on the surface. However, in all cases of smectite surfaces artificially devoid of ions, a water droplet is always formed and the wetting is incomplete. The contact angles of the water droplets on charged montmorillonites are very similar to that on uncharged pyrophyllite surface and range roughly between 110o and 90o. These angles are also affected by the distribution of the octahedral and tetrahedral substitutions in the structure and by their ratio. In the case of purely tetrahedral substitutions the contact angle on the bare smectite surface can be as low as ~60o, but still far from complete wetting.
The angular distributions of the H2O dipole vectors as a function of distance from the smectite surface show two preferred surface-oriented types of water molecules when counterions are present, and the total surface is highly hydrophilic. However, for surfaces devoid of ions, a population with dipole angles close to ~90o is dominating, and the smectite surfaces can be considered hydrophobic. It can be thus concluded that, independent of the structural charge, bare smectite surfaces by themselves are either hydrophobic or only moderately hydrophilic. Their experimentally observed highly hydrophilic character is almost entirely due to the charge balancing cations present on the surface.
In this paper, we formulate a field-theoretical model of dilute salt solutions of electrically neutral spherical colloid particles. Each colloid particle consists of a 'central' charge that is situated at the center and compensating peripheral charges (grafted to it) that are fixed or fluctuating relative to the central charge. In the framework of the random phase approximation, we obtain a general expression for electrostatic free energy of solution and analyze it for different limiting cases. In the limit of infinite number of peripheral charges, when they can be modelled as a continual charged cloud, we obtain an asymptotic behavior of the electrostatic potential of a point-like test charge in a salt colloid solution at long distances, demonstrating the crossover from its monotonic decrease to damped oscillations with a certain wavelength. We show that the obtained crossover is determined by certain Fisher-Widom line. For the same limiting case, we obtain an analytical expression for the electrostatic free energy of a salt-free solution. In the case of nonzero salt concentration, we obtain analytical relations for the electrostatic free energy in two limiting regimes. Namely, when the ionic concentration is much higher than the colloid concentration and the effective size of charge cloud is much bigger than the screening lengths that are attributed to the salt ions and the central charges of colloid particles. The proposed theory could be useful for theoretical description of the phase behavior of salt solutions of metal-organic complexes and polymeric stars.
Microdisk lasers having a III–V core coated with a TiO2 shell are experimentally studied under optical pumping. Initial core microdisk lasers with a 5–10 μm diameter comprising five layers of InAs∕In0.15Ga0.85As quantum dots demonstrate room temperature lasing with excellent characteristics (threshold, quality factor) at the ground state optical transition in the 1.28–1.30 μm spectral range. Deposition of the TiO2 dielectric shell results in a decimation of the whispering gallery modes of the microdisk resonator and, for thicker (>100 nm) shells, in a blueshift of the lasing wavelength. Using numerical analysis, we demonstrate that coating a III–V core microdisk with a high-index shell causes strong penetration of the second and third radial modes into the shell, whereas the first radial mode remains nearly undisturbed. Though optical loss added by the TiO2 dielectric shell is low (it does not exceed 2 cm−1 even for a 250-nm-thick TiO2 layer), mode leakage to the TiO2 results in a decrease in the optical confinement factor and an increase in the threshold pump power. This effect is more pronounced in microlasers of the smallest diameter studied (5 μm). Thus, in addition to other applications, a TiO2 shell can be used for mode selection in microdisk lasers or for selective outcoupling of the emission to the waveguide structure, which requires proper adjustment of the TiO2 shell thickness and microdisk diameter.
The energy-to-data ratio (EDR) was evaluated for quantum-dot based microdisk laser directly modulated without external cooling. The experimental values of EDR decrease with decreasing diameter of the microdisk and reach 1.5 pJ/bit for the smallest diameter under study (10.5 μm). In larger microdisks (with a diameter greater than 20 μm), the EDR varies in proportion to the square of the diameter. If this relationship were true for smaller microdisks as well, an EDR value of about 100 fJ would be achieved with a diameter of 4 μm. The observed deviation of EDR from the quadratic dependence on the diameter is associated with an increase in the threshold current density in smaller devices, which in turn may be caused by the contribution of nonradiative recombination on the microresonator sidewalls formed by deep etching.
We report on direct large signal modulation and the reliability studies of microdisk lasers based on InGaAs/GaAs quantum well-dots. A 23 μm in diameter microlaser exhibits an open eye diagram up to 12.5 Gbit/s and is capable of error-free 10 Gbit/s data transmission at 30°C without temperature stabilization. The ageing tests of a 31 μm in diameter microdisk laser were conducted at room and elevated temperatures during more than 1200 hr. The average rate of the output power degradation was about 25 and 29 nW/hr at 40°C and 60°C, respectively.
GaAs-based microdisk lasers with an active region representing a dense array of indium-rich islands (InGaAs quantum well-dots) were studied using direct small-signal modulation. We demonstrate that using dense arrays of InGaAs quantum well-dots enables uncooled high-frequency applications with a GHz-range bandwidth for microdisk lasers. A maximum 3 dB modulation frequency of 5.9 GHz was found in the microdisk with a radius of 13.5 μm operating without a heatsink for cooling. A modulation current efficiency factor of 1.5 GHz∕mA1∕2 was estimated.
The development of a fast semiconductor laser is required for the realization of next-generation telecommunication applications. Since lasers operating on quantum dot ground state transitions exhibit only limited gain due to the saturation effect, we investigate lasing from excited states and compare its corresponding static and dynamic behavior to the one from the ground state. InAs quantum dots (QDs) grown in dot-in-well (DWELL) structures allowed to obtain light emission from ground and three excited states in a spectral range of 1.0–1.3 μm. This emission was coupled to whispering gallery modes (WGMs) of a 6 μm microdisk resonator and studied at room temperature by steady-state and time-resolved micro-photoluminescence. We demonstrate a cascade development of lasing arising from the ladder of quantum dot states, and compare the lasing behavior of ground and excited state emission. While the lasing threshold is being increased from the ground state to the highest excited state, the dynamic behavior is improved: turn-on times and lifetimes of WGMs become shorter paving the way towards high frequency direct driven microlasers.