Virtual Gate Research Articles

Experimental computations of atomic properties on a superconducting quantum processor

We experimentally compute relativistic and correlation effects in the atomic properties by using a superconducting qubit processor. Specifically, we compute the relativistic ground-state energies and magnetic-dipole hyperfine structure constants for four Li-like atomic systems ranging from very light to moderately heavy to very heavy in terms of nuclear charge. A symmetry-conserving Bravyi-Kitaev transformation is used to reduce the original six-qubit problem to a four-qubit problem, which is experimentally contrived by reducing the hardware requirement by employing a virtual two-qubit gate. It enables the simulation of four-qubit circuits using two physical qubits with additional circuit evaluations. The ground-state wave functions, required for computing atomic properties, are obtained by using quantum state tomography. Our results show that the averaged relative errors for the ground-state energies are ≈0.3±1%. However, for the hyperfine structure constants, the mean values of the relative errors are less than 15%, with their estimated upper bound of relative errors of ≈±10% (with the exception of 7.2±47% for neutral Li7). Notably, our results for the hyperfine structure constants exhibit higher sensitivity to errors as compared to energies; a trend which we also confirm through additional numerical simulations. Published by the American Physical Society 2024

Experimental demonstration of a high-fidelity virtual two-qubit gate

We experimentally demonstrate a virtual two-qubit gate and characterize it using quantum process tomography (QPT). The virtual two-qubit gate decomposes an actual two-qubit gate into single-qubit unitary gates and projection gates in quantum circuits for expectation-value estimation. We implement projection gates via midcircuit measurements. The deterministic sampling scheme reduces the number of experimental circuit evaluations required for decomposing a virtual two-qubit gate. We also apply quantum error mitigation to suppress the effect of measurement errors and improve the average gate fidelity of a virtual controlled-Z (CZ) gate to fav=0.9938±0.0002. Our results highlight a practical approach to implement virtual two-qubit gates with high fidelities, which are useful for simulating quantum circuits using fewer qubits and implementing two-qubit gates on a distant pair of qubits. Published by the American Physical Society 2024

Effect of Laser Therapy, Neurodynamic Stabilization and Strengthening Exercises on Hand Function in Patients of Carpal Tunnel Syndrome with Rheumatoid Arthritis- A Narrative Review

Background: Carpal tunnel syndrome (CTS) is an entrapment neuropathy in which median nerve is compressed or squeezed at the wrist level in the carpal tunnel. Carpal tunnel syndrome is the most prevalent neurological complication in the rheumatoid arthritis patients. The prevalence of CTS in RA ranged from 3.5% to 22.8 %. Tenosynovitis, inflammation of the synovial tissue of the flexor tendons, can cause increased pressure in the carpal tunnel and result in CTS. Hand function is usually affected in carpel tunnel syndrome which affects the daily living performance by affecting both gross motor activities like grasping, carrying, holding and fine motor activities like writing, gripping and buttoning the shirts. Laser therapy, also called as photo biomodulation, can reduce pain, inflammation, swelling and synovitis. The dexterity and functionality of the hands improved through hand and wrist stretching and strengthening exercises.
 Objective: To find out the effect of laser therapy, neurodynamic mobilization exercises and strengthening exercises on hand function in patients of carpal tunnel syndrome with rheumatoid arthritis.
 Study selection: This narrative review is conducted on databases from Pubmed, Google scholar, scopus, web of knowledge, Virtual Health Library, Research Gate and Cochrane library in Nov 2023.

Effect of Source–Drain Opposite Side Gate on the AlGaN/GaN High Electron Mobility Transistor Devices

To explore the influence of different gate positions on the performance of AlGaN/GaN high electron mobility transistor devices, two model structures are proposed in this paper: an inverted T‐type gate and source–drain opposite side structure (ITGS–DOSS), and an embedded ITGS–DOSS. It is shown in the simulation results that compared with the traditional T‐type gate structure, these two structures have better transfer characteristics and significantly reduce the on‐state resistance, which can effectively improve the virtual gate effect and suppress the current collapse effect. Furthermore, these two structures can also improve the frequency characteristics of the device, with a maximum cutoff frequency of about 625 and 635 GHz, respectively. The threshold voltage of the ITGS–DOSS is about −30 V, which is significantly shifted to the left compared to the traditional T‐type structure. With a gate–drain spacing of 4.4 μm, the breakdown voltage is still as high as 1661 V. As the device size and gate–drain spacing decrease, this structure has better voltage withstand characteristics, thus achieving low threshold and high breakdown device performance.

Study on the Point‐Contact Gate AlGaN/GaN High Electron Mobility Transistor with 0.1 μm Gate Length

The current collapse has been one of the most challenging problems in AlGaN/GaN high electron mobility transistors (HEMTs). In recent years, the virtual gate effect has been the most widely accepted cause of the current collapse effect. To effectively improve the current collapse effect and reduce the influence of the virtual gate effect on the device, a point‐contact gate AlGaN/GaN HEMT structure is proposed in this article. Tests show that the device has high transconductance, high cut‐off frequency, and good transfer, output, and breakdown characteristics. The maximum saturation drain current is 18 mA mm−1, the maximum transconductance is 200 mS mm−1, the breakdown voltage is 994 V, the maximum current gain is about 190 dB, and the cut‐off frequency is up to 206 GHz when the gate length and width are 0.1 μm × 0.001 μm. The experimental analysis shows that the point‐contact gate AlGaN/GaN HEMT structure shortens the gate length, thereby improving the virtual gate effect and effectively suppressing the current collapse effect, increasing the breakdown voltage of the device, and further improving the device performance, which lays the foundation for the future research of AlGaN/GaN HEMT.

Error suppression by a virtual two-qubit gate

Sparse connectivity of a superconducting quantum computer results in large experimental overheads of SWAP gates. In this study, we consider employing a virtual two-qubit gate (VTQG) as an error suppression technique. The VTQG enables a non-local operation between a pair of distant qubits using only single qubit gates and projective measurements. Here, we apply the VTQG to the digital quantum simulation of the transverse-field Ising model on an IBM quantum computer to suppress the errors due to the noisy two-qubit operations. We present an effective use of VTQG, where the reduction in multiple SWAP gates results in increasing the fidelity of output states. The obtained results indicate that the VTQG can be useful for suppressing the errors due to additional SWAP gates. In our experiments, we have observed one order of magnitude improvement in accuracy for the quantum simulation of the transverse-field Ising model with 8 qubits. Finally, we have demonstrated an efficient implementation of the VTQG by utilizing dynamic circuits. This scheme reduces experimental overheads for implementing m VTQGs from O(10m) to O(6m).

Development and Implementation of a Direct Evaluation Solution for Fault Tree Analyses Competing With Traditional Minimal Cut Sets Methods

Fault tree analysis (FTA) is a well-established technique to analyze the safety risks of a system. Two specific prominent FTA methods, largely applied in the aerospace field, are the so-called minimal cut sets (MCS), which uses an approximate evaluation of the problem, and the direct evaluation (DE) of the fault tree, which uses a top-down recursive algorithm. The first approach is only valid for small values of basic event probabilities and has historically yielded faster results than exact solutions for complex fault trees. The second one means exact solutions at a higher computational cost. This article presents several improvements applied to both approaches in order to upgrade the computing performance. First, improvements to the MCS approach have been performed, where the main idea has been to optimize the number of required permutations and to take advantage of the available information from previous solved subsets. Second, improvements to the DE approach have been applied, which deal with a reduction of the number of recursive calls through a deep search for independent events in the fault tree. This could dramatically reduce the computation time for industrial fault trees with a high number of repeated events. Additional implementation improvements have been also applied regarding hash tables, and memory access and usage, but also implementing the so-called “virtual gates”, which enable limitless children on each gate. The results presented hereafter are promising, not only because they show that both approaches have been highly optimized compared to the literature, but also because a DE solution has been achieved, which can compete in time resources (and obviously in precision) with the MCS approach. These improvements are relevant when considering the industrial, and more specifically the aeronautical, implementation and application of both techniques.

Hot Carrier Injection (HCI) Reliability of Fabricated Y-gate HEMT with Various Top Length

Device degradation due to hot carrier injection (HCI) in different Y-gate HEMT devices is thoroughly analyzed. To further understand the HCI reliability of the Y-gate HEMT devices, the device is fabricated with AlGaN/GaN structure with different top lengths (Ltop). An HCI stress time of 6000 s was conducted on these devices, while V t stability in other stress time domains, leakage current, and transconductance degradation are also discussed. In this work, we have demonstrated that increasing the LTop length could avoid the virtual gate effect and disperse the influence of the electric field under HCI stress. Furthermore, the effects of trapping in various locations, such as in the bulk SiN or AlGaN/GaN interface has been discussed. These trapping effects caused by the HCI stress might be the source of the Vth shift. Overall, The large Y-gate HEMT showed the lowest degradation of DC characteristics after the long HCI stress test.

Development of a virtual quality gate concept based on high-potential tests for lithium-ion battery cell manufacturing

Lithium-ion batteries (LIB) are considered a prominent energy storage technology, especially in the field of electromobility. In this sense, early quality control of battery cell manufacturing is crucial as it can increase energy and material efficiency by stopping further production of critical cells. This paper proposes a virtual quality gate (VQG) concept for inline quality control of battery cell manufacturing. Based on that, only the cells that meet the predefined quality requirements can proceed to the next process steps. For quality control, the VQG includes high-potential tests (HiPot), a measurement method to characterize the electrical insulation properties of separator layers under a defined electrical voltage. As a use case, the Effects of the lamination process of electrodes and separators on cell quality are investigated using the VQG. Data-driven modeling is implemented to predict and classify cell quality concerning the process parameters of lamination. As a result, early-failure detection and better decision-making for battery cell manufacturing are achieved, increasing efficiency from both economic and environmental perspectives.

Accuracy verification of magnetic sensors in different weather conditions

An intelligent transport system cannot exist without high-quality information about transport. One of the possibilities for data collection is a sensory transport network. The city of Žilina has a wireless network of magnetic sensors built a few years ago. I continuously collect traffic information. It monitors all lanes in the direction to and from the city center. The sensors thus create an area bounded by virtual gates which count entering and exiting vehicles. The sensory network sends obtained data by each sensor to a publicly accessible database. This article also describes mentioned database that provides the traffic flow characteristics – intensity, speed, and classification of vehicles. The question of the magnetic sensors used is their accuracy. Their function is counting, speed measuring, and vehicle classification. Sensors detect all these characteristics based on the magnetic field changes by passing vehicles. In this paper, the authors verify the accuracy of the sensors in two traffic surveys in warm weather and winter conditions. In both surveys, certain deviations were evident, but they did not fundamentally affect the accuracy of vehicle counting.

Towards an integrated control system for a scrap-free circular production of lithium-ion batteries

Battery production is an energy-intensive process with scrap rates between 5 % and 30 %. Therefore, concepts such as in-production recycling and Circulation Factories can improve energy and resource efficiency by connecting production and recycling operations. The secondary material, or more specifically the post-production material from recycling is a new variable in the production system and its amount varies according to the scrap rate. To handle resulting process interrelations and overall equipment efficiency in production and recycling, data from both has to be merged and considered coherently. Additionally, final product quality is affected by material degradation effects due to multiple feeding of already recycled post-production material. Based on cyber-physical control systems with elements such as virtual quality gates, an architecture for an operations control system in the circular production is proposed and transferred to the production of battery cells. This system should be able to consider different production goals such as product quality as well as material and energy efficiency. Therefore, the developed architecture reveals process interrelations using data mining and proposes adjustments to the set of control variables. Finally, different approaches are investigated and a “simple-to-complex-roadmap” for the practical implementation of operations control systems in circular production is derived.

Building Blocks for an Automated Quality Assurance Concept in High Throughput Battery Cell Manufacturing

The increasing demand for sustainable energy raises the request for battery cells. Industry and research are faced with challenges like complex processes, complex machinery, and many intra-process interactions within the field of battery cell production. Major problems, such as low process stability and quality fluctuations, lead to high scrap rates. Result is a reduced sustainability in the production process. To address these challenges, the main content of this paper is a conceptual design of a virtual Quality Gate (QG) system, for quality assurance and quality prediction. The concept of virtual QG combines physical and digital elements. On the physical side actuators, sensors, and measurement technologies are included to provide the raw data. The digital side of virtual QG includes necessary elements for data acquisition, data processing, data analysis and information provision for the decision-making process in the real world. Focus of the presented approach is illustrating how to select the appropriate location of QG for quality decisions in conjunction with the derivation of necessary decisions, process information and evaluation of measurement technology that is needed.

Life Cycle Gates: Extending the concept of Virtual Quality Gates along circular product life cycles

Reaching a higher level of sustainability of a products life cycle became a strategic goal for many companies over the past years. To achieve that higher level of sustainability, the transformation of linear product life cycles (cradle to grave) into circular life cycles (cradle to cradle) in the context of a Circular Economy (CE) is one promising approach. However, implementing a circular life cycle results in higher requirements in defining the best fitted strategy at the end of each product use stage depending on economic, environmental and social factors.In order to cope these increased requirements, the whole product life cycle has to become more transparent. This transparency can be reached by a holistic digital representation and virtual quality control of all life cycle stages. To implement a virtual quality control in each stage and enable the monitoring and controlling of the whole life cycle, the concept of Virtual Quality Gates can be extended. Virtual Quality Gates divide a defined manufacturing chain into different virtual, quality-relevant decision points to check the product quality and ensure a defined quality state before further manufacturing steps are approved. This concept can be transferred to each life cycle stage to ensure a holistic optimization of the products life cycle quality and an optimized selection of a strategy at the end of each use stage.This paper presents a framework for the implementation of virtual quality gates into product life cycles. These extended quality gates are defined as Life Cycle Gates, which are virtual decision points to optimize a product life cycle. The demand and applicability of the concept is shown for a mechanical recycling process of automotive parts.

Ultrathin Interfacial Layer and Pre-Gate Annealing to Suppress Virtual Gate Formation in GaN-Based Transistors: The Impact of Trapping and Fluorine Inclusion

In AlGaN/GaN high electron mobility transistors (HEMTs), the long-term operation of the device is adversely affected by threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\text{V}_{\text{th}}}$ </tex-math></inline-formula> ) instability and current collapse. In this letter, using structural and electrical analyses, the impact of trapping and fluorine (F) inclusion on the device operation is scrutinized. It is found that SiNx interfacial layer significantly reduced the formation of defects, during the ohmic annealing process. Moreover, the incorporation of F ions into GaN bulk, during the gate etch process, triggers the virtual gate phenomenon. This effect has also been mitigated via the pre-gate annealing (PGA) process. As a result of these modifications, a stable operation with minimized lag performance has been achieved.

An automated approach for consecutive tuning of quantum dot arrays

Recent progress has shown that the dramatically increased number of parameters has become a major issue in tuning of multi-quantum dot devices. The complicated interactions between quantum dots and gate electrodes cause the manual tuning process to no longer be efficient. Fortunately, machine learning techniques can automate and speed up the tuning of simple quantum dot systems. In this Letter, we extend the techniques to tune multi-dot devices. We propose an automated approach that combines machine learning, virtual gates, and a local-to-global method to realize the consecutive tuning of quantum dot arrays by dividing them into subsystems. After optimizing voltage configurations and establishing virtual gates to control each subsystem independently, a quantum dot array can be efficiently tuned to the few-electron regime with appropriate interdot tunnel coupling strength. Our experimental results show that this approach can consecutively tune quantum dot arrays into an appropriate voltage range without human intervention and possesses broad application prospects in large-scale quantum dot devices.

On the Onset of Breakdown of the Virtual Gate in AlGaN/GaN HEMTs

On the Onset of Breakdown of the Virtual Gate in AlGaN/GaN HEMTs

High-fidelity CNOT gate for spin qubits with asymmetric driving using virtual gates

Recent experiments have demonstrated two-qubit fidelities above 99%, however, theoretically, the fidelity of CNOT operations is limited by off-resonant driving described by off-diagonal terms in the system Hamiltonian. Here we investigate these off-diagonal contributions and we propose a fidelity improvement of several orders of magnitude by using asymmetric driving. Therefore, we provide a description of an ac virtual gate based on a simple capacitance model which not only enables a high fidelity CNOT but also crosstalk reduction when scaling up spin qubit devices to larger arrays.

Using data-mining techniques to improve combinatorial optimization algorithms

In this work, we show how data-mining can be used to cluster algorithmic generated data and use that data to improve algorithms that solve combinatorial optimization problems for a real-world application—the field-programmable gate array placement problem. Our methodology is a means for other algorithm engineers to improve their own algorithms for specific real-world problems that are hard to improve. In our case, the placement algorithms are difficult to improve, and to find better heuristics we analyze the results of placement solutions to find clustered information which can then be used to improve the algorithms. Specifically, we show a technique for gathering cluster information about placement, we create a new simulated annealing algorithm and a new genetic algorithm that can deal with a mixed granularity of placement objects on a virtual field-programmable gate array, and we show that these algorithms either execute faster or improve the overall quality of solution compared to their basic algorithm without this clustering data and improved heuristics. For our improved simulated annealing placer we improve the algorithms run-time by 17% across a range of benchmarks, and our genetic algorithm improves placement metrics—-critical path by 10% and channel-width by 4%.

Reverse bias annealing effects in N-polar GaN/AlGaN metal-insulator-semiconductor high electron mobility transistors

Reverse bias annealing (RBA) is applied to N-polar GaN high electron mobility transistors (HEMTs) to improve the quality of the gate stack interface. As demonstrated for Ga-polar HEMTs, RBA improves the stability of the gate stack interface. However, the decrease in the maximum drain current density is observed as a unique phenomenon for the N-polar HEMTs. The calculation of the band profile suggests that in the N-polar HEMTs the electrons injected from the gate electrode by the reverse bias accumulate at the gate stack interface in the extrinsic gate region. This promotes the electron trapping in the gate stack, which results in an increase in the source access resistance by the virtual gate phenomenon. In the Ga-polar HEMTs, the electrons tend to accumulate at the AlGaN/GaN interface rather than the gate stack interface, which gives less chance of the virtual gate phenomenon.

A novel AlGaN/GaN heterostructure field-effect transistor based on open-gate technology

In this study, a novel AlGaN/GaN heterostructure field-effect transistor based on open-gate technology was fabricated. Sample transistors of different structures and sizes were constructed. Through measurements, it was found that by changing the width of the opening, the threshold voltage of the device could be easily modulated across a larger range. The open-gate device had two working modes with different transconductance. When the gate-source voltage VGS ≤ − 4.5 V, only the open region was conductive, and a new working mechanism modulated the channel current. Corresponding theoretical analysis and calculations showed that its saturation mechanism was related to a virtual gate formed by electron injection onto the surface. Also, the gate-source voltage modulated the open channel current by changing the channel electron mobility through polarization Coulomb field scattering. When used as class-A voltage amplifiers, open-gate devices can achieve effective voltage amplification with very low power consumption.