3,266 results on '"DOT"'
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2. Smart textile lighting/display system and future quantum dot light emitting diode
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Yang, Jiajie and Kim, Jong Min
- Subjects
Display ,Quantum Dot ,Smart Textile - Abstract
The aim of this research is to develop a smart textile system based on multifunctional input and output electronic fibre devices. Unlike planar/rigid display devices, this research proposes not only a novel device architecture but also its integration into a textile system by using conventional yarn-to-textile methodologies, such as weaving and knitting. Smart lighting/display textile with multifunctional fibre devices has great potential in numerous areas, including lighting, display, smart home and Internet of Thing (IoT). This thesis first introduces the existing technology in textile engineering, including conventional fibre material and textile fabrication technology followed by the latest development in smart textile, which covers topics of functional fibre materials and devices. Conductive yarn is the fundamental for fibre-electronics and smart textile. The developed silver-polyamide (Ag-PA) conductive fibre shows an excellent electrical conductivity and mechanical robustness up to 35% strain. The F-touch and F-RF fabricated from Ag-PA also exhibits an excellent bending durability. The Field- effect transistor (FET) based F-biosensor shows a threshold voltage V_TH of 0.9 V, an ON/OFF ratio of 10⁸, and a saturation mobility μ_sat of 8 cm²/V·s which is comparable to the state-of-the-art flexible transistors. The F-temperature and F- energy demonstrated the viability of true core-shell cylindrical structure device for temperature measurement and energy storage that could withstand more than 900 bending cycles. As an output component, F-LEDs (fibre light-emitting diode) embedded 34-inch 6536-pixel full colour large area display represents the highest resolution full colour textile display reported to the date. The integrated smart textile has functions including touch detection, electrocardiogram (ECG) bio-signal measurement, temperature monitoring, far- field ultraviolet (UV) detection, wireless power transmission with RF signal, energy storage and video/image/information displaying. To further improve the display unit, a quantum dot light-emitting diode (QDLED) based textile display was developed. The electrode with lab synthesized silver nanowire (AgNW) shows a figure of merit (FoM) of 0.0014. The optimised MoO₃/Au electrode exhibits a transmittance of T₅₅₀= 81%, sheet resistance of Rs = 17.92 and a FoM of 0.0077. Both electrodes show a superior mechanical bending durability beyond the indium tin oxide (ITO) electrode. The optimisation was carried out on QDLED devices to ensure their performance meets the requirements for smart textile. The reduced phosphomolybdic acid hole injection layer (PMA-r HIL) based device exhibits a luminance that is comparable to the poly(3,4- ethylenedioxythiophene) with poly(4-sulfonate) (PEDOT:PSS) HIL based device and an even higher external quantum efficiency (EQE). The novel double layer PMA-r/PEDOT:PSS HIL device shows a remarkable 11.33% EQE. A remarkable lifetime of T₇₅ = 1019 h is achieved using MoO₃/Au/PMA-r device. The bending test also shows such device is able to maintain its luminance over 15000 cd/m² after 500 bending cycles at a bending radius of 5 mm. On the system level, a novel lateral driving architecture for smart textile display was developed and examined. The innovative architecture greatly simplifies the interconnection and tackles the resolution and stability issue encountered by other textile display architecture. The woven textile display is the world's first full color QDLED textile display with high pixels per inch (PPI) scalability.
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- 2022
- Full Text
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3. Electron transport through and in quantum dot arrays
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Bayer, Johannes Christian and Bayer, Johannes Christian
- Abstract
The present thesis investigates serial quantum dot arrays of different sizes, the double quantum dot, the triple quantum dot, and the quadruple quantum dot. The quantum dot device is based on a two-dimensional electron gas formed in a GaAs/AlGaAs heterostructure. A quantum point contact in the vicinity of the quantum dots is utilized as a charge sensor, allowing to detect tunneling of single electrons into or out of the quantum dots as well as between two of the quantum dots. Two qualitatively different regimes are discussed, the transport regime and the isolated regime. In the transport regime, where the quantum dots are well coupled to electron reservoirs on both sides, electrons can tunnel from one reservoir to the other through the array. Gate voltage dependent measurements are used to characterize the transport properties through the quantum dot arrays and to extract electrostatic properties. For all array sizes, long-range transport across quantum dots in Coulomb blockade is observed for the strong coupling regime. The isolated regime is reached by increasing the tunnel barriers between reservoirs and the quantum dot array on both sides until tunneling from and into the reservoirs is fully suppressed within the measurement timescales. The number of electrons in an isolated array is fixed, but electrons can still be redistributed inside the array. The charge reconfiguration inside the arrays is tracked using the charge detector. A high level of control over the coupling, and thus the interdot transitions, including long-range transitions between non-neighboring quantum dots, is demonstrated. Time-resolved charge detection was used to investigate the tunneling dynamics of a single, two, and three electrons loaded into a double quantum dot, where the three electron case shows a high sensitivity to environmental parameters.
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- 2024
4. Highly ordered inkjet-printed quantum-dot thin films enable efficient and stable QLEDs with EQE exceeding 23%
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Wei, Changting, Xu, Bo, Zhang, Meng, Su, Zhenhuang, Gu, Jiawei, Guo, Wenrui, Gao, Xingyu, Su, Wenming, Cui, Zheng, Jeon, Seokwoo, Fan, Zhiyong, Zeng, Haibo, Wei, Changting, Xu, Bo, Zhang, Meng, Su, Zhenhuang, Gu, Jiawei, Guo, Wenrui, Gao, Xingyu, Su, Wenming, Cui, Zheng, Jeon, Seokwoo, Fan, Zhiyong, and Zeng, Haibo
- Abstract
Inkjet-printed quantum dot light-emitting diodes (QLEDs) are emerging as a promising technology for next-generation displays. However, the progress in fabricating QLEDs using inkjet printing technique has been slower compared to spin-coated devices, particularly in terms of efficiency and stability. The key to achieving high performance QLEDs lies in creating a highly ordered and uniform inkjet-printed quantum dot (QD) thin film. In this study, we present a highly effective strategy to significantly improve the quality of inkjet-printed CdZnSe/CdZnS/ZnS QD thin films through a pressure-assisted thermal annealing (PTA) approach. Benefiting from this PTA process, a high quality QD thin film with ordered packing, low surface roughness, high photoluminescence and excellent electrical property is obtained. The mechanism behind the PTA process and its profound impact on device performance have been thoroughly investigated and understood. Consequently, a record high external quantum efficiency (EQE) of 23.08% with an impressive operational lifetime (T50) of up to 343,342 h@100 cd m−2, and a record EQE of 22.43% with T50 exceeding to 1,500,463 h@100 cd m−2 are achieved in inkjet-printed red and green CdZnSe-based QLEDs, respectively. This work highlights the PTA process as an important approach to realize highly efficient and stable inkjet-printed QLEDs, thus advancing QLED technology to practical applications. © 2024 The Authors
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- 2024
5. Development of Quantum Dot Sources at Telecom C-band for Single/Entangled Photon Generation
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Larrondo, Jorge and Larrondo, Jorge
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Semiconductor quantum dots (QDs) are prime candidates for single and entangled photon sources in quantum information technologies due to their unique optical properties. This thesis investigates the development of QD sources operating at the telecom C-band ---around 1550 nm---, a critical aspect for long-distance applications in optical fibers. The research focuses on the design and optimization of InAs/GaAs QDs for efficient single photon emission within the telecom C-band. This thesis delves into the optimization of the quantum dot environment, by etching its matrix as a microlens (ML). The design process utilizes both simulations and lab fabrication techniques to achieve a source with high single photon throughput, a key requirement for quantum key distribution (QKD). To achieve this, the design optimizes factors such as material growth techniques, device structures, and microlens array configuration to enhance light collection efficiency by a microscope objective and Purcell effect for higher single-photon emission rate. The optimized microlens geometries, particularly the Gaussian and hemispherical shapes, significantly enhanced light extraction efficiency by the objective, achieving up to 40\% and 35\% respectively. The combined fabrication techniques of FIB milling, photolithography, and dry etching resulted in upgraded optical properties and minimal scattering in the microlenses. Furthermore, this work builds upon previous research conducted at the Royal Institute of Technology (KTH). The Quantum Nano Photonics (QNP) group successfully employed QDs to generate entangled photon states. This thesis extends this research by focusing on the design and optimization of a telecom C-band QD source suitable for long-distance transmission through existing fiber optic infrastructure over the Greater Stockholm Metropolitan Area, i.e. between the QNP-group lab at KTH AlbaNova campus and Ericsson HQ, in Kista, Stockholm. The feasibility of such transmission is explored by, Halvledarkvantprickar (QD) är utmärkta kandidater för enstaka och sammanflätade fotonkällor i kvantinformationsteknik på grund av deras unika optiska egenskaper. Denna avhandling undersöker utvecklingen av QD-källor som strålar på telekom C-band ---cirka 1550 nm---, en kritisk aspekt för långdistansapplikationer i optiska fiber. Forskningen fokuserar på design och optimering av InAs/GaAs QDs för effektiv emission av enstaka fotoner inom telekom C-bandet. Denna avhandling fördjupar sig i utformningen av kvantprickarkällan, med hjälp av en mikrolins (ML) array. Designprocessen använder både simuleringar och tillverkningstekniker för att uppnå en källa med hög enfotonrenhet, ett viktigt krav för kvantnyckeldistribution (QKD). För att uppnå detta optimerar designen faktorer som materialtillväxttekniker, enhetsstrukturer och mikrolinskonfiguration för att förbättra ljusinsamlingseffektiviteten och Purcell-effekten för ljusare och snabbare emission av enstaka fotoner. De optimerade mikrolinsgeometrierna, särskilt de gaussiska och halvsfäriska formerna, förbättrade avsevärt ljusextraktionseffektiviteten och nådde upp till 40\% respektive 35\%. De kombinerade tillverkningsteknikerna FIB-fräsning, fotolitografi och torretsning resulterade i uppgraderade optiska egenskaper och minimal spridning i de mikrolinserna. Vidare bygger detta arbete på tidigare forskning som bedrivits vid Kungliga Tekniska Högskolan (KTH). Quantum Nano Photonics-gruppen (QNP) använde framgångsrikt QD för att generera sammanflätade fotontillstånd. Denna avhandling utvidgar denna forskning genom att fokusera på design och optimering av en telekom C-band QD-källa lämplig för långdistansöverföring genom befintlig fiberoptisk infrastruktur över Storstockholmsområdet, dvs. mellan QNP-gruppens labb på KTH AlbaNova campus och Ericssons huvudkontor i Kista, Stockholm. Genomförbarheten av sådan överföring undersöks genom att demonstrera överföringen av enstaka fotoner från en QD-källa i QNP-labbet på KTH till E
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- 2024
6. Strong Light-Matter Coupling in Lead Halide Perovskite Quantum Dot Solids
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Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), European Commission, Junta de Andalucía, Air Force Office of Scientific Research (US), Office of Naval Research (US), Bujalance, Clara, Calió, Laura, Dirin, Dmitry N., Tiede, David O., Galisteo-López, Juan F., Feist, Johannes, García-Vidal, Francisco J., Kovalenko, Maksym V., Míguez, Hernán, Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), European Commission, Junta de Andalucía, Air Force Office of Scientific Research (US), Office of Naval Research (US), Bujalance, Clara, Calió, Laura, Dirin, Dmitry N., Tiede, David O., Galisteo-López, Juan F., Feist, Johannes, García-Vidal, Francisco J., Kovalenko, Maksym V., and Míguez, Hernán
- Abstract
Strong coupling between lead halide perovskite materials and optical resonators enables both polaritonic control of the photophysical properties of these emerging semiconductors and the observation of fundamental physical phenomena. However, the difficulty in achieving optical-quality perovskite quantum dot (PQD) films showing well-defined excitonic transitions has prevented the study of strong light-matter coupling in these materials, central to the field of optoelectronics. Herein we demonstrate the formation at room temperature of multiple cavity exciton-polaritons in metallic resonators embedding highly transparent Cesium Lead Bromide quantum dot (CsPbBr3-QD) solids, revealed by a significant reconfiguration of the absorption and emission properties of the system. Our results indicate that the effects of biexciton interaction or large polaron formation, frequently invoked to explain the properties of PQDs, are seemingly absent or compensated by other more conspicuous effects in the CsPbBr3-QD optical cavity. We observe that strong coupling enables a significant reduction of the photoemission line width, as well as the ultrafast modulation of the optical absorption, controllable by means of the excitation fluence. We find that the interplay of the polariton states with the large dark state reservoir plays a decisive role in determining the dynamics of the emission and transient absorption properties of the hybridized light-quantum dot solid system. Our results should serve as the basis for future investigations of PQD solids as polaritonic materials.
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- 2024
7. Strong light-matter coupling in lead halide perovskite quantum dot solids [Dataset]
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Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), European Commission, Junta de Andalucía, Air Force Office of Scientific Research (US), Office of Naval Research (US), Míguez, Hernán [0000-0003-2925-6360], Míguez, Hernán [h.miguez@csic.es], Bujalance, Clara, Calió, Laura, Dirin, Dmitry N., Tiede, David O., Galisteo-López, Juan F., Feist, Johannes, García-Vidal, Francisco J., Kovalenko, Maksym V., Míguez, Hernán, Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), European Commission, Junta de Andalucía, Air Force Office of Scientific Research (US), Office of Naval Research (US), Míguez, Hernán [0000-0003-2925-6360], Míguez, Hernán [h.miguez@csic.es], Bujalance, Clara, Calió, Laura, Dirin, Dmitry N., Tiede, David O., Galisteo-López, Juan F., Feist, Johannes, García-Vidal, Francisco J., Kovalenko, Maksym V., and Míguez, Hernán
- Abstract
Strong coupling between lead halide perovskite materials and optical resonators enables both the polaritonic control of the photophysical properties of these emerging semiconductors and the observation of novel fundamental physical phenomena. However, the difficulty to achieve optical-quality perovskite quantum dot (PQD) films showing well-defined excitonic transitions has prevented the study of strong light-matter coupling in these materials, central to the field of optoelectronics. Herein we demonstrate the formation at room temperature of multiple cavity exciton-polaritons in metallic resonators embedding highly transparent Cesium Lead Bromide quantum dot (CsPbBr3-QD) solids, revealed by a significant reconfiguration of the absorption and emission properties of the system. Our results indicate that the effects of biexciton interaction or large polaron formation, frequently invoked to explain the properties of PQDs, are seemingly absent or compensated by other more conspicuous effects in the CsPbBr3-QD optical cavity. We observe that strong coupling enables a significant reduction of the photoemission linewidth, as well as the ultrafast modulation of the optical absorption, controllable by means of the excitation fluence. We find that the interplay of the polariton states with the large dark state reservoir play a decisive role in determining the dynamics of the emission and transient absorption properties of the hybridized light-quantum dot solid system. Our results open the route for the investigation of PQD solids as polaritonic optoelectronic materials.
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- 2024
8. Spectroscopy of hot electron pair emission from a driven quantum dot
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Schulenborg, Jens, Fletcher, Jonathan D., Kataoka, Masaya, Splettstoesser, Janine, Schulenborg, Jens, Fletcher, Jonathan D., Kataoka, Masaya, and Splettstoesser, Janine
- Abstract
On-demand emission of individual electrons for the implementation of flying qubits and quantum electron-optics experiments requires precise knowledge and tunability of emission times and energies. Crucially, for confined electron sources such as driven quantum dots, the effect of local Coulomb interaction on these emission properties needs to be understood, in particular if multiple particles are emitted close in time or near simultaneously. This paper theoretically analyzes electron pair emission from an ac driven quantum dot, detailing the competing effects of the electron-electron interaction, the time-dependent potential forming the quantum dot, and of the quantum-state properties, such as degeneracy, on the emission times and energies. We complement a numerical analysis of the coherent Schrödinger evolution of two particles in a driven potential with a master-equation description for strongly interacting electrons tunneling stochastically into a weakly coupled conductor. This captures a broad range of different influences on the emitted particles and thereby guides the development of single-electron sources with higher control over two-particle emission properties., On-demand emission of individual electrons for the implementation of flying qubits and quantum electron-optics experiments requires precise knowledge and tunability of emission times and energies. Crucially, for confined electron sources such as driven quantum dots, the effect of local Coulomb interaction on these emission properties needs to be understood, in particular if multiple particles are emitted close in time or near simultaneously. This paper theoretically analyzes electron pair emission from an ac driven quantum dot, detailing the competing effects of the electron-electron interaction, the time-dependent potential forming the quantum dot, and of the quantum-state properties, such as degeneracy, on the emission times and energies. We complement a numerical analysis of the coherent Schrödinger evolution of two particles in a driven potential with a master-equation description for strongly interacting electrons tunneling stochastically into a weakly coupled conductor. This captures a broad range of different influences on the emitted particles and thereby guides the development of single-electron sources with higher control over two-particle emission properties.
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- 2024
9. Development of high-performance, cost-effective quantum dot lasers for data-centre and Si photonics applications
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Lu, Ying
- Abstract
Photonic technologies have been considered new methods to achieve high bandwidth data communication and transmission. Si-photonics was proposed to address the discrepancy between bulky photonic devices and advanced electronics and create high-density integrated photonics. One of the challenges is integrating all the components necessary for full-functionality photonic integrated circuits (PIC). Great efforts have been devoted to overcoming the inherent limitations of Group-IV materials to provide sufficient gain, efficient modulation and sensitive detections. Making Si the host material for efficient light emission poses the most stringent requirements and is the primary missing component in the Si-photonics platform. Incorporating III-V materials with the Si photonics platform and quantum dot (QD) structure is a promising solution to the problem of a fully-integrated and high-functioning PIC. High-performance QD lasers on III-V substrate or epitaxially on silicon have been developed in the last few decades with low threshold current density, low-temperature sensitivity, great reliability and large injection efficiency. Moreover, from the dynamic aspect, the intrinsic frequency of direct modulated laser and noise intensity is important for its applications in a data centre. QD is considered an alternative to quantum wells (QWs); however, the demonstrated QD laser has not fulfilled initial expectations, mainly due to its high gain compression and low differential gain. Another feature that needs to be noticed is feedback sensitivity, as the properties of semiconductor lasers are greatly degraded by reflection from external reflectors, such as the fibre connects and facets of integrated devices. QD devices are predicted to have stronger feedback resistance due to their large damping and small linewidth enhancement factor (LEF). These properties have attracted much research, and high-performance QD devices have been developed. In this thesis, we comprehensively investigated QD laser performance and applied our QD laser in the optical module instead of the commercial QW distributed feedback (DFB) laser. The background of Si photonics, the development of QD devices, and the fundamentals of QD lasers are presented in Chapter 1. The basic static and dynamic performances are demonstrated in Chapters 2 and 3. The GaAs-based QD laser provides a low threshold, high-temperature stability, and low noise operation with a limited small signal bandwidth. Chapter 4 provides a comprehensive study of the feedback resistance of the QD laser. The onset of coherence collapse is determined as -14 dB, verified by the static optical and electrical spectra and small signal response. Based on previous measurements, the QD laser is proven to be a high-performance, low-cost candidate for the Si-photonics module. In Chapter 5, the QD laser is used in practical applications, including a large signal transmission system with and without feedback and a commercial optical module. Although the intrinsic bandwidth of the QD laser is limited to around 5GHz due to the large damping and unoptimised capacitance, 30 Gbps data transmission has been demonstrated by a directly modulated QD laser. Large, high-speed signal modulation is achieved due to its high gain compression factor. Regarding the laser with intentional feedback, there is little degradation in the eye diagram under the whole feedback level up to -8dB. We also replaced the commercial QW DFB laser in 100G data-centre reach (DR)-1 optical module with our QD Fabry Perot (FP) laser without an isolator which gives a clear eye diagram under 53 Gbps 4-level pulse amplitude modulation (PAM4) with an extinction ratio (ER) of 4.7 dB. In conclusion, this thesis verifies the feasibility of adopting the QD laser as a light source for the Si-photonics module. The QD laser is selected over other lasers because of its low threshold, high-temperature stability and maximum operating temperature, and strong tolerance to unintentional feedback. This is the first project to measure critical feedback levels with different characteristics and to theoretically analyse the inconsistent value. More importantly, this thesis' most original contribution is investigating the commercial applications of QD lasers in a Si-photonics module in an isolator-free state. In summary, the QD laser has been proven to be a feasible solution for the next-generation optical system.
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- 2023
10. Oscillating photonic Bell state from a semiconductor quantum dot for quantum key distribution
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Pennacchietti, Matteo, Cunard, Brady, Nahar, Shlok, Zeeshan, Mohd, Gangopadhyay, Sayan, Poole, Philip J., Dalacu, Dan, Fognini, Andreas, Jöns, Klaus D., Zwiller, Val, Jennewein, Thomas, Lütkenhaus, Norbert, Reimer, Michael E., Pennacchietti, Matteo, Cunard, Brady, Nahar, Shlok, Zeeshan, Mohd, Gangopadhyay, Sayan, Poole, Philip J., Dalacu, Dan, Fognini, Andreas, Jöns, Klaus D., Zwiller, Val, Jennewein, Thomas, Lütkenhaus, Norbert, and Reimer, Michael E.
- Abstract
An on-demand source of bright entangled photon pairs is desirable for quantum key distribution (QKD) and quantum repeaters. The leading candidate to generate such pairs is based on spontaneous parametric down-conversion (SPDC) in non-linear crystals. However, its pair extraction efficiency is limited to 0.1% when operating at near-unity fidelity due to multiphoton emission at high brightness. Quantum dots in photonic nanostructures can in principle overcome this limit, but the devices with high entanglement fidelity (99%) have low pair extraction efficiency (0.01%). Here, we show a measured peak entanglement fidelity of 97.5% ± 0.8% and pair extraction efficiency of 0.65% from an InAsP quantum dot in an InP photonic nanowire waveguide. We show that the generated oscillating two-photon Bell state can establish a secure key for peer-to-peer QKD. Using our time-resolved QKD scheme alleviates the need to remove the quantum dot energy splitting of the intermediate exciton states in the biexciton-exciton cascade., QC 20240311
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- 2024
- Full Text
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11. Développement d’électronique froide à base de memristors pour la mise à l’échelle des calculateurs quantiques à base de boîtes quantiques
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Drouin, Dominique, Pioro-Ladrière, Michel, Mouny, Pierre-Antoine, Drouin, Dominique, Pioro-Ladrière, Michel, and Mouny, Pierre-Antoine
- Abstract
L’informatique quantique promet un impact social important en accélérant les avancées dans des domaines tels que la recherche médicale, l’ingénierie des matériaux et la modélisation climatique. Un défi technologique important de mise à l’échelle des bits quantiques (qubits) doit cependant être surmonté pour accéder à ces applications. Une telle mise à l’échelle requiert de réduire le nombre d’entrées/sorties entre l’électronique classique de contrôle et les qubits présents dans le cryostat, notamment dans le cadre des qubits sur silicium manipulés par des grilles électrostatiques. Chaque grille doit être connectée à l’électronique de contrôle par un câble sortant du cryostat limitant la taille des systèmes. Pour répondre aux exigences de cette mise à l’échelle, cette thèse de doctorat propose un concept d’électronique de contrôle froide basé des mémoires résistives (memristors) à base de TiOx. Ces composants présentent les avantages d’être non-volatile et d’avoir une résistance modifiable de manière analogique. La compatibilité avec les températures cryogéniques de ces memristors est démontrée jusqu’à 1.2 K. Ils présentent une programmation entièrement analogique sur une plage de résistance de 10 kΩ à 100 kΩ notamment permis par la mise en évidence du procédé de reforming cryogénique. Le concept de source de tension DC à base de memristors consiste à placer plusieurs memristors en parallèle dans la boucle de rétroaction d’un amplificateur transimpédance. Ainsi en changeant la résistance des memristors, le gain de l’amplificateur est changé et la tension de sortie est modifiée. La viabilité de ce concept est ensuite étudiée en réalisant des simulations basées sur des données expérimentales de caractérisations électriques de memristors TiOx. Le concept de source de tension DC à base de memristors démontre une plage de tension supérieure à 1 V et une résolution en tension de 1 mV répondant ainsi aux critères de polarisation pour les boîtes quantiques. La simulation du, Quantum computing promises to have a major social impact, accelerating advances in fields such as medical research, materials engineering and climate modeling. However, the technological challenge of scaling up qubits must be overcome before these applications can be realized. Such scaling requires a reduction of the inputs/outputs between the classical control electronics and the qubits in the cryostat, particularly in the case of silicon qubits controlled by electrostatic gates. Each gate must be biased by control electronics placed outside of the cryostat, limiting the size of maximum the quantum systems. To meet these scaling requirements, this PhD thesis proposes a concept for cryogenic control electronics based on TiOx memristors. These components offer the advantages of being non-volatile and having a fully analog programmability. These devices have been demonstrated to be compatible with cryogenic temperatures down to 1.2 K during this thesis. They feature fully analog programming over a resistance range from 10 kΩ to 100 kΩ, which is enabled by the cryogenic reforming process. The concept of a memristor-based DC source involves placing several memristors in parallel in the feedback loop of a transimpedance amplifier. Thus, by changing the resistance of the memristors, the gain of the amplifier is changed which yields to the tuning of the amplifier output voltage. The feasibility of this concept is then investigated by carrying out data-driven simulations based on data from cryogenic electrical characterizations of TiOx memristors. The memristor-based DC source concept demonstrates a voltage range of 1 V and a voltage resolution of 1 mV, thus meeting the biasing criteria for quantum dots. Simulations of the bising of a quantum dot by a memristors-based DC source hasvealso been carried out, demonstrating a low-noise charge stability diagram, thus validating the proposed concept. Finally, an experimental prototype was built using a commercial amplif
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- 2024
12. Can People Accurately Draw Statistical Inferences from Dot Plots?
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Jaramillo, Sara, Jaramillo, Sara, Rottman, Benjamin, Jaramillo, Sara, Jaramillo, Sara, and Rottman, Benjamin
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What sorts of graphical formats best convey effect size and degree of certainty of a finding? Confidence intervals are commonly used to show uncertainty, yet lay people and experts fail to correctly interpret their meaning. There has been a recent push to present individual data points rather than only presenting aggregated summary statistics (e.g., means, confidence intervals, lines of best fit). But it is unclear how well people can aggregate raw data presented in a graphical format. Across two studies, we presented participants with hypothetical study outcomes of two independent groups in three graph styles: dot plots, mean with 95% confidence interval (CI) plots, combined plots, and bee plots. We asked participants to make judgments about the effect size using the Common Language Effect Size or Bayes Factors. Participants were more likely to underestimate effect sizes and Bayes Factors for dot plots and bee plots compared to mean + 95% CI plots and combined plots. These findings suggest that people have trouble making statistical inferences when presented with raw data points in graphs.
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- 2024
13. Bandgap study of quantum dot-sized SiGe alloy nanocrystals prepared in a nonthermal capacitively-coupled plasma by ambient scanning tunneling spectroscopy
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Uddin, Md Seraj, Khatun, Salma, Vijayan, C., Rath, J. K., Uddin, Md Seraj, Khatun, Salma, Vijayan, C., and Rath, J. K.
- Abstract
The manuscript aims to elucidate the evolution of the bandgap and the semiconducting nature of quantum dot-sized SiGe alloy nanocrystals prepared at different plasma conditions in VHF PECVD. The technique of scanning tunneling spectroscopy (STS) is used for this, considering its highly localized nature, and to study the individual NCs. The STS analysis gives the density of states (DOS) spectrum of the SiGe alloy NCs. The present STS study reveals a dependence of the bandgap of SiGe alloy NCs on plasma parameters. The SiGe alloy NCs also exhibited a shallow p-type character despite the fact that no dopants were used during the deposition. Besides this, the midgap defect states are also observed in some of the samples. Further, a comparative bandgap study of the SiGe alloy NCs with its bulk indicates quantum confinement. These new findings from the QD-sized SiGe alloy NCs are important for the conceptual design and practical development of quantum dot-based third-generation solar cells.
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- 2024
14. Stability Study of Quantum Dot Color Converted Mini/Micro-LED Displays
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Cheng, Yuanjie, Lo, Chi Chuen, Qiu, Xing, Xu, Hua, Tao, Mian, Lee, Shi-wei, Cheng, Yuanjie, Lo, Chi Chuen, Qiu, Xing, Xu, Hua, Tao, Mian, and Lee, Shi-wei
- Abstract
The implementation of quantum dot color conversion (QDCC) technology in mini/micro-LED display applications has attracted considerable interest due to its remarkable fabrication yield and superior optical performance. However, the stability problems of the QDCC devices need to be addressed as they can lead to a significant decrease in light output. This study explores the stability of QDCC film under thermal heat and moisture conditions, particularly at 85°C5% RH and 85°C85%RH. The results of our study demonstrate that the QDCC film is susceptible to degradation from moisture. Moreover, our investigation reveals that the QDCC film with a protection coating exhibits a much better stability compared to the sample lacking such a coating. © 2024 Japan Institute of Electronics Packaging.
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- 2024
15. Passive mode-locking of p-doped quantum dot semiconductor lasers
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Auth, D., Korenev, V. V., Savelyev, A. V., Maximov, M. V., Zhukov, A. E., Breuer, S., Auth, D., Korenev, V. V., Savelyev, A. V., Maximov, M. V., Zhukov, A. E., and Breuer, S.
- Abstract
Quantum dot based monolithic edge-emitting semiconductor lasers at 1.25 µm are ideal sources for the generation of broad optical frequency combs for optical communication applications. In this work, InAs/InGaAs quantum dot lasers with different total laser length to absorber length ratio and with different p-doping concentrations in the GaAs barrier sections are investigated experimentally in dependence on the gain injection current and absorber reverse bias voltage. A smaller mode-locking area is found for the p-doped device in dependence on the laser biasing conditions. For the undoped active region 1.3 ps short pulse widths at a pulse repetition rate of 20 GHz with a pulse-to-pulse timing jitter of 111 fs are reported for an absorber section length of 12% to the total cavity length. For an undoped and p-doped device short pulse emission between 2.5 ps and 5.5 ps is attained and a shorter absorber section length of 8% or 5%.
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- 2024
16. Mechanism of quantum yield enhancement in Si quantum dots by high-pressure water vapor annealing from single-dot studies
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Lu, Xi, Zhou, Jingjian, Gelloz, Bernard, Sychugov, Ilya, Lu, Xi, Zhou, Jingjian, Gelloz, Bernard, and Sychugov, Ilya
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High-pressure water vapor annealing (HWA) was recently demonstrated as a method that can substantially improve the photoluminescence quantum yield (PLQY) of silicon quantum dots (Si QDs) with the oxide shell. In this Letter, the mechanism of this enhancement is studied optically on a single-dot level. HWA treatment is performed on Si QDs formed on a silicon-on-insulator wafer, and their photoluminescence (PL) properties were examined before and after the treatment. Our experiments show a 2.5 time enhancement in the average blinking duty cycle of Si QDs after 2.6 MPa HWA treatment without changing the average ON-state PL intensity. This observation proves the carrier trapping process is suppressed on the HWA-built Si/SiO2 interface. We also discussed the mechanism behind the PLQY enhancement of HWA-treated Si QDs by comparing single-dot-level data to reported ensemble PL Si QDs results. HWA treatment is found to mainly brighten "grey" (not 100% efficient) QDs, a mechanism different from changing dark (non-emitting) to bright (100% efficient) Si QDs by ligand passivation.
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- 2024
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17. Autonomous self-healing hybrid energy harvester based on the combination of triboelectric nanogenerator and quantum dot solar cell
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Xiao, Tianxiao, Tu, Suo, Tian, Ting, Chen, Wei, Cao, Wei, Liang, Suzhe, Guo, Renjun, Liu, Liangzhen, Li, Yanan, Guan, Tianfu, Liu, Haochen, Wang, Kai, Schwartzkopf, Matthias, Fischer, Roland A., Roth, Stephan V., Müller-Buschbaum, Peter, Xiao, Tianxiao, Tu, Suo, Tian, Ting, Chen, Wei, Cao, Wei, Liang, Suzhe, Guo, Renjun, Liu, Liangzhen, Li, Yanan, Guan, Tianfu, Liu, Haochen, Wang, Kai, Schwartzkopf, Matthias, Fischer, Roland A., Roth, Stephan V., and Müller-Buschbaum, Peter
- Abstract
Realization of multi-source energy harvesting with one single device would maximize power output. Thus, it is emerging as a promising strategy towards renewable energy generation and has attracted worldwide attention in the past decades. Capable of capturing mechanical energy that is ubiquitous in the ambient environment, triboelectric nanogenerator (TENG) has been considered a novel yet effective source towards next-generation energy harvesting. In this work, a flexible hybrid energy harvester (HEH) is developed via the rational integration of autonomous self-healing TENG and high bending-stable lead sulfide quantum dot (PbS QD) solar cell, enabling independent electricity generation by two different mechanisms. The single-electrode mode TENG component with self-healing is realized by a polydimethylsiloxane/Triton X-100 (PDMS/TX100) mixture as the dielectric layer and the shared gold (Au) electrode, which generates 0.39 µA of output current (Iout), 24.6 V of output voltages (Vout), 15.4 nC of transfer charges (Qsc), and 7.80 mW m−2 of output power peak density. The thin-film solar cell component is based on a PbS QD layer as the light absorber with a planar structure fabricated under low-cost and compatible conditions, achieving 22.8 mA cm−2 of short-circuit current density (Jsc) and 4.92% of power conversion efficiency (PCE). As a proof of concept, an electronic watch is successfully powered by harnessing ambient mechanical and solar energy with a hybridized energy cell. This approach will offer more opportunities to construct a versatile platform towards remote monitoring and smart home systems., QC 20240424
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- 2024
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18. Certification Grade Quantum Dot Luminescent Solar Concentrator Glazing with Optical Wireless Communication Capability for Connected Sustainable Architecture
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Meinardi, F, Bruni, F, Castellan, C, Meucci, M, Umair, A, La Rosa, M, Catani, J, Brovelli, S, Meinardi, Francesco, Bruni, Francesco, Castellan, Claudio, Meucci, Marco, Umair, Ali Muhammad, La Rosa, Marcello, Catani, Jacopo, Brovelli, Sergio, Meinardi, F, Bruni, F, Castellan, C, Meucci, M, Umair, A, La Rosa, M, Catani, J, Brovelli, S, Meinardi, Francesco, Bruni, Francesco, Castellan, Claudio, Meucci, Marco, Umair, Ali Muhammad, La Rosa, Marcello, Catani, Jacopo, and Brovelli, Sergio
- Abstract
Energy sustainability and interconnectivity are the two main pillars on which cutting-edge architecture is based and require the realization of energy and intelligent devices that can be fully integrated into buildings, capable of meeting stringent regulatory requirements and operating in real-world conditions. Luminescent solar concentrators, particularly those based on near-infrared emitting reabsorption-free quantum dots, are considered good candidates for the realization of semi-transparent photovoltaic glazing, but despite important advances in optical property engineering strategies, studies of finished devices suitable for real-world operation are still lacking. In this paper, the first example of a fully assembled quantum dot luminescent solar concentrator-based photovoltaic glazing is demonstrated that meets all international standards for photovoltaic and building elements. It is also shown that these devices are capable of functioning as efficient Visible Light Communication (VLC) receivers even under full sunlight, thus combining energy and wireless connectivity functions in a realistic solution for smart, sustainable buildings.
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- 2024
19. Electron-hole asymmetric magnetotransport of graphene-colloidal quantum dot device
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Huang, Yuqing, Kang, N., Huang, Yuqing, and Kang, N.
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Interfacing graphene with other low-dimensional material has gained attentions recently due to its potential to stimulate new physics and device innovations for optoelectronic and electronic applications. Here, we exploit a solution-processed approach to introduce colloidal quantum dot (CQD) to the bilayer graphene device. The magnetotransport properties of the graphene device is drastically altered due to the presence of the CQD potential, leading to the observation of AB-like oscillation in the quantum Hall regime and screening of the intervalley scattering. The anomalous magnetotransport behavior is attributed to the coulombic scattering introduced by the CQDs and is shown to be highly asymmetric depending on the polarity of the transport carriers. These results prove the potential of such flexible method for engineering microscopic scattering process and performance of the graphene device that may lead to intriguing device application in such hybrid system., Funding Agencies|National Natural Science Foundation of China [12374035, 11974026]; National Key Research and Devel- opment Program of China [2017YFA0303304]; Science Foundation of Jihua Laboratory [2021B0301030003-03]; Knut and Alice Wallenberg Foundation [KAW 2020.0029]
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- 2024
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20. The Utility of Dot Phrases and SmartPhrases in Improving Physician Documentation of Interpreter Use
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Jaradeh, Katrin, Jaradeh, Katrin, Hsiang, Elaine, Singh, Malini K., Peabody, Christopher R., Straube, Steven, Jaradeh, Katrin, Jaradeh, Katrin, Hsiang, Elaine, Singh, Malini K., Peabody, Christopher R., and Straube, Steven
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Background: Patients with limited English proficiency (LEP) experience significant healthcare disparities. Clinicians are responsible for using and documenting their use of certified interpreters for patient encounters when appropriate. However, the data on interpreter use documentation in the emergency department (ED) is limited and variable. We sought to assess the effects of dot phrase and SmartPhrase implementation in an adult ED on the rates of documentation of interpreter use.Methods: We conducted an anonymous survey asking emergency clinicians to self-report documentation of interpreter use. We also retrospectively reviewed documentation of interpreter-services use in ED charts at three time points: 1) pre-intervention baseline; 2) post-implementation of a clinician-driven dot phrase shortcut; and 3) post-implementation of a SmartPhrase.Results: Most emergency clinicians reported using an interpreter “almost always” or “often.” Our manual audit revealed that at baseline, interpreter use was documented in 35% of the initial clinician note, 4% of reassessments, and 0% of procedure notes; 52% of discharge instructions were written in the patients’ preferred languages. After implementation of the dot phrase and SmartPhrase, respectively, rates of interpreter-use documentation improved to 43% and 97% of initial clinician notes, 9% and 6% of reassessments, and 5% and 35% of procedure notes, with 62% and 64% of discharge instructions written in the patients’ preferred languages.Conclusion: There was a discrepancy between reported rates of interpreter use and interpreter-use documentation rates. The latter increased with the implementation of a clinician-driven dot phrase and then a SmartPhrase built into the notes. Ensuring accurate documentation of interpreter use is an impactful step in language equity for LEP patients.
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- 2024
21. Effect of Connectivity on the Carrier Transport and Recombination Dynamics of Perovskite Quantum-Dot Networks
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Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Junta de Andalucía, European Commission, Wake Forest University, Tiede, David O., Romero-Pérez, Carlos, Koch, Katherine A., Ucer, K. Burak, Calvo, Mauricio E., Srimath Kandada, Ajay Ram, Galisteo-López, Juan F., Míguez, Hernán, Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Junta de Andalucía, European Commission, Wake Forest University, Tiede, David O., Romero-Pérez, Carlos, Koch, Katherine A., Ucer, K. Burak, Calvo, Mauricio E., Srimath Kandada, Ajay Ram, Galisteo-López, Juan F., and Míguez, Hernán
- Abstract
Quantum-dot (QD) solids are being widely exploited as a solution-processable technology to develop photovoltaic, light-emission, and photodetection devices. Charge transport in these materials is the result of a compromise between confinement at the individual QD level and electronic coupling among the different nanocrystals in the ensemble. While this is commonly achieved by ligand engineering in colloidal-based systems, ligand-free QD assemblies have recently emerged as an exciting alternative where nanostructures can be directly grown into porous matrices with optical quality as well as control over their connectivity and, hence, charge transport properties. In this context, we present a complete photophysical study comprising fluence- and temperature-dependent time-resolved spectroscopy to study carrier dynamics in ligand-free QD networks with gradually varying degrees of interconnectivity, which we achieve by changing the average distance between the QDs. Analysis of the photoluminescence and absorption properties of the QD assemblies, involving both static and time-resolved measurements, allows us to identify the weight of the different recombination mechanisms, both radiative and nonradiative, as a function of QD connectivity. We propose a picture where carrier diffusion, which is needed for any optoelectronic application and implies interparticle transport, gives rise to the exposure of carriers to a larger defect landscape than in the case of isolated QDs. The use of a broad range of fluences permits extracting valuable information for applications demanding either low- or high-carrier-injection levels and highlighting the relevance of a judicious design to balance recombination and diffusion.
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- 2024
22. Effect of Connectivity on the Carrier Transport and Recombination Dynamics of Perovskite Quantum-Dot Networks [Dataset]
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Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), European Commission, Junta de Andalucía, Wake Forest University, Calvo, Mauricio E. [0000-0002-1721-7260], Míguez, Hernán [0000-0003-2925-6360], Tiede, David O., Romero-Pérez, Carlos, Koch, Katherine A., Ucer, K. Burak, Calvo, Mauricio E., Srimath Kandada, Ajay Ram, Galisteo-López, Juan F., Míguez, Hernán, Ministerio de Ciencia e Innovación (España), Agencia Estatal de Investigación (España), European Commission, Junta de Andalucía, Wake Forest University, Calvo, Mauricio E. [0000-0002-1721-7260], Míguez, Hernán [0000-0003-2925-6360], Tiede, David O., Romero-Pérez, Carlos, Koch, Katherine A., Ucer, K. Burak, Calvo, Mauricio E., Srimath Kandada, Ajay Ram, Galisteo-López, Juan F., and Míguez, Hernán
- Abstract
Quantum-dot (QD) solids are being widely exploited as a solution-processable technology to develop photovoltaic, light-emission, and photodetection devices. Charge transport in these materials is the result of a compromise between confinement at the individual QD level and electronic coupling among the different nanocrystals in the ensemble. While this is commonly achieved by ligand engineering in colloidal-based systems, ligand-free QD assemblies have recently emerged as an exciting alternative where nanostructures can be directly grown into porous matrices with optical quality as well as control over their connectivity and, hence, charge transport properties. In this context, we present a complete photophysical study comprising fluence- and temperature-dependent timeresolved spectroscopy to study carrier dynamics in ligand-free QD networks with gradually varying degrees of interconnectivity, which we achieve by changing the average distance between the QDs. Analysis of the photoluminescence and absorption properties of the QD assemblies, involving both static and timeresolved measurements, allows us to identify the weight of the different recombination mechanisms, both radiative and nonradiative, as a function of QD connectivity. We propose a picture where carrier diffusion, which is needed for any optoelectronic application and implies interparticle transport, gives rise to the exposure of carriers to a larger defect landscape than in the case of isolated QDs. The use of a broad range of fluences permits extracting valuable information for applications demanding either low- or high-carrier-injection levels and highlighting the relevance of a judicious design to balance recombination and diffusion.
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- 2024
23. Exciton Transport in a Germanium Quantum Dot Ladder
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Hsiao, T. (author), Cova Fariña, P. (author), Oosterhout, S.D. (author), Jirovec, D. (author), Zhang, X. (author), van Diepen, C.J. (author), Lawrie, W.I.L. (author), Wang, C.A. (author), Sammak, A. (author), Scappucci, G. (author), Veldhorst, M. (author), Vandersypen, L.M.K. (author), Hsiao, T. (author), Cova Fariña, P. (author), Oosterhout, S.D. (author), Jirovec, D. (author), Zhang, X. (author), van Diepen, C.J. (author), Lawrie, W.I.L. (author), Wang, C.A. (author), Sammak, A. (author), Scappucci, G. (author), Veldhorst, M. (author), and Vandersypen, L.M.K. (author)
- Abstract
Quantum systems with engineered Hamiltonians can be used to study many-body physics problems to provide insights beyond the capabilities of classical computers. Semiconductor gate-defined quantum dot arrays have emerged as a versatile platform for realizing generalized Fermi-Hubbard physics, one of the richest playgrounds in condensed matter physics. In this work, we employ a germanium 4×2 quantum dot array and show that the naturally occurring long-range Coulomb interaction can lead to exciton formation and transport. We tune the quantum dot ladder into two capacitively coupled channels and exploit Coulomb drag to probe the binding of electrons and holes. Specifically, we shuttle an electron through one leg of the ladder and observe that a hole is dragged along in the second leg under the right conditions. This corresponds to a transition from single-electron transport in one leg to exciton transport along the ladder. Our work paves the way for the study of excitonic states of matter in quantum dot arrays., QCD/Vandersypen Lab, BUS/TNO STAFF, QCD/Veldhorst Lab, QCD/Scappucci Lab, QN/Veldhorst Lab, QN/Vandersypen Lab
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- 2024
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24. Evaluation of Lag of Accommodation with Full-Field Diffusion Optics Technology™ (DOT) Contrast Management Spectacle Lenses in Emmetropic Children
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Jabeen,Asiya, Luensmann,Doerte, Woods,Jill, Hill,Jennifer, Jones,Lyndon, Jabeen,Asiya, Luensmann,Doerte, Woods,Jill, Hill,Jennifer, and Jones,Lyndon
- Abstract
Asiya Jabeen,1 Doerte Luensmann,1 Jill Woods,1 Jennifer S Hill,2 Lyndon Jones1 1Centre for Ocular Research & Education (CORE), School of Optometry & Vision Science, University of Waterloo, Waterloo, ON, Canada; 2SightGlass Vision, Inc, Palo Alto, CA, USACorrespondence: Asiya Jabeen, Centre for Ocular Research & Education (CORE), School of Optometry & Vision Science, University of Waterloo, Waterloo, ON, Canada, Tel +1 519-888-5467, Ext. 36210, Fax +1 519-888-4303, Email ajabeen@uwaterloo.caPurpose: To evaluate the impact on the lag of accommodation (LOA) in emmetropic children after short-term wear of full-field Diffusion Optics TechnologyTM (DOT) spectacle lenses, designed to modulate retinal contrast to control myopia progression.Patients and Methods: This was a single-visit, prospective, randomized, subject-masked study of emmetropes (ametropes ± 1.00D or less in each meridian) with no history of myopia control treatment. Unaided logMAR visual acuity was measured, and ocular dominance was determined using the sighting method. In a randomized order, participants wore plano full-field contrast management (DOT) spectacles (no clear central aperture) or control spectacles (standard single vision spectacle lenses). Each participant was given 5 minutes for adaptation to the respective lenses before open field autorefraction measurements were taken at 6 meters and 40 cm. Ten measurements were taken for each eye. Data were evaluated from the right eye and the dominant eye separately.Results: A total of 30 participants (20 females and 10 males) with a mean age of 10.4 ± 2.8 (7 to 17) years completed the study. There was no significant difference in right eye mean LOA with contrast management spectacles 0.57 ± 0.39D versus control spectacles 0.62 ± 0.34D; Wilcoxon test, p = 0.37. For dominant eyes, LOA values were 0.60 ± 0.40D and 0.68 ± 0.33D with contrast management spectacles and control spectacles, respectively (p = 0.14). Additionally, no signifi
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- 2024
25. Perancangan Sistem Tampilan Informasi Kelas Pelatihan Menggunakan Dot Matrix P10 dan Security Door Lock Berbasis Arduino: Studi Kasus di BBPVP Bekasi
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Rhomadon, Ahmad Arif Falah, Arifin, Muhammad Latif, Sunardi, Ariyawan, Rhomadon, Ahmad Arif Falah, Arifin, Muhammad Latif, and Sunardi, Ariyawan
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Ruang kelas menjadi sarana dalam melaksanakan kegiatan belajar mengajar pada berbagai jenis pembelajaran, seperti pembelajaran sekolah formal dan sekolah informal. Kondisi belajar yang kondusif sangat diperlukan untuk proses belajar yang optimal. Pada ruang kelas di BBPVP Bekasi Jurusan Teknik Elektronika gedung Workshop Elektronika, seringkali terjadi interupsi saat kegiatan belajar mengajar berlangsung. Akibatnya kegiatan belajar menjadi tidak kondusif karena interupsi dari instruktur atau siswa pelatihan salah masuk ruang kelas. Karena itu, dibuat alat pengunci pintu otomatis beserta akses masuk berupa sensor RFID, sekaligus tampilan kelas pelatihan beserta waktu real time yang ditampilkan pada Dot Matrix P10 berbasis Arduino. Akses masuk kelas hanya dapat diakses pada jam aktif kegiatan belajar, yaitu pukul 07.00-15.00 WIB, kecuali akses instruktur yang dapat diakses kapanpun. Alat tersebut diterapkan di ruang kelas lab 11 pelatihan BBPVP Bekasi Gedung Workshop Elektronika dan mampu menurunkan interupsi saat kegiatan belajar sedang berlangsung sehingga kegiatan belajar menjadi lebih kondusif.
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- 2024
26. A phase transition between positional and semantic learning in a solvable model of dot-product attention
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Cui, Hugo, Behrens, Freya, Krzakala, Florent, Zdeborová, Lenka, Cui, Hugo, Behrens, Freya, Krzakala, Florent, and Zdeborová, Lenka
- Abstract
We investigate how a dot-product attention layer learns a positional attention matrix (with tokens attending to each other based on their respective positions) and a semantic attention matrix (with tokens attending to each other based on their meaning). For an algorithmic task, we experimentally show how the same simple architecture can learn to implement a solution using either the positional or semantic mechanism. On the theoretical side, we study the learning of a non-linear self-attention layer with trainable tied and low-rank query and key matrices. In the asymptotic limit of high-dimensional data and a comparably large number of training samples, we provide a closed-form characterization of the global minimum of the non-convex empirical loss landscape. We show that this minimum corresponds to either a positional or a semantic mechanism and evidence an emergent phase transition from the former to the latter with increasing sample complexity. Finally, we compare the dot-product attention layer to linear positional baseline, and show that it outperforms the latter using the semantic mechanism provided it has access to sufficient data.
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- 2024
27. Dot-depth three, return of the J-class
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Place, Thomas, Zeitoun, Marc, Place, Thomas, and Zeitoun, Marc
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We look at concatenation hierarchies of classes of regular languages. Each such hierarchy is determined by a single class, its basis: level $n$ is built by applying the Boolean polynomial closure operator (BPol), $n$ times to the basis. A prominent and difficult open question in automata theory is to decide membership of a regular language in a given level. For instance, for the historical dot-depth hierarchy, the decidability of membership is only known at levels one and two. We give a generic algebraic characterization of the operator BPol. This characterization implies that for any concatenation hierarchy, if $n$ is at least two, membership at level $n$ reduces to a more complex problem, called covering, for the previous level, $n-1$. Combined with earlier results on covering, this implies that membership is decidable for dot-depth three and for level two in most of the prominent hierarchies in the literature. For instance, we obtain that the levels two in both the modulo hierarchy and the group hierarchy have decidable membership.
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- 2024
28. Quantum dot-based thermal spectroscopy and imaging of optically trapped microspheres and single cells
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Haro-González, P., Ramsay, W.T., Martínez Maestro, Laura, Del Rosal, B., Santacruz-Gomez, K., Iglesias-De La Cruz, M.D.C., Sanz-Rodríguez, F., Chooi, J.Y., Sevilla, P.R., Bettinelli, M., Choudhury, D., Kar, A.K., Solé, J.G., Jaque, D., Paterson, L., Haro-González, P., Ramsay, W.T., Martínez Maestro, Laura, Del Rosal, B., Santacruz-Gomez, K., Iglesias-De La Cruz, M.D.C., Sanz-Rodríguez, F., Chooi, J.Y., Sevilla, P.R., Bettinelli, M., Choudhury, D., Kar, A.K., Solé, J.G., Jaque, D., and Paterson, L.
- Abstract
Laser-induced thermal effects in optically trapped microspheres and single cells are investigated by quantum dot luminescence thermometry. Thermal spectroscopy has revealed a non-localized temperature distribution around the trap that extends over tens of micrometers, in agreement with previous theoretical models besides identifying water absorption as the most important heating source. The experimental results of thermal loading at a variety of wavelengths reveal that an optimum trapping wavelength exists for biological applications close to 820 nm. This is corroborated by a simultaneous analysis of the spectral dependence of cellular heating and damage in human lymphocytes during optical trapping. This quantum dot luminescence thermometry demonstrates that optical trapping with 820 nm laser radiation produces minimum intracellular heating, well below the cytotoxic level (43 degrees C), thus, avoiding cell damage., Universidad Autonoma de Madrid, Comunidad Autónoma de Madrid, Ministerio de Educación y Ciencia (España), Malta Consolider-Ingenio, Caja Madrid Foundation, Fondazione Cariverona, Fundacion Dr. Manuel Morales, Banco Santander, CEAL-UAM through the UAM-NUS cooperation project, UK Research & Innovation (UKRI), Engineering & Physical Sciences Research Council (EPSRC), Heriot Watt University Life Science Interface Theme Scholarship, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub
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- 2024
29. Generating Shuttling Procedures for Constrained Silicon Quantum Dot Array
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Sato, Naoto, Sekiguchi, Tomonori, Utsugi, Takeru, Mizuno, Hiroyuki, Sato, Naoto, Sekiguchi, Tomonori, Utsugi, Takeru, and Mizuno, Hiroyuki
- Abstract
In silicon quantum computers, a single electron is trapped in a microstructure called a quantum dot, and its spin is used as a qubit. For large-scale integration of qubits, we previously proposed an approach of arranging the quantum dots in a two-dimensional array and sharing a control gate in a row or column of the array. In our array, the shuttling of electrons is a useful technique to operate the target qubit independently and avoid crosstalk. However, since the shuttling is also conducted using shared control gates, the movement of qubits is complexly constrained. We therefore propose a formal model on the basis of state transition systems to describe those constraints and operation procedures on the array. We also present an approach to generate operation procedures under the constraints. Utilizing this approach, we present a concrete method for our 16 $\times$ 8 quantum dot array. By implementing the proposed method as a quantum compiler, we confirmed that it is possible to generate operation procedures in a practical amount of time for arbitrary quantum circuits. We also demonstrated that crosstalk can be avoided by shuttling and that the fidelity in that case is higher than when crosstalk is not avoided.
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- 2024
30. Reducing the Impact of Defects in Quantum-Dot Cellular Automata (QCA) Approximate Adders at Nano Scale
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Alfonso Sanchez-Macian, Alonso Martin-Toledano, Jefferson Andres Bravo-Montes, García Herrero, Francisco Miguel, Juan Antonio Maestro, Alfonso Sanchez-Macian, Alonso Martin-Toledano, Jefferson Andres Bravo-Montes, García Herrero, Francisco Miguel, and Juan Antonio Maestro
- Abstract
Quantum-dot Cellular Automata (QCA) has been studied for some time as a candidate to replace traditional CMOS circuits. QCA circuits are implemented using majority-logic gates and inverters as primitive elements. Different types of defects affecting QCA during synthesis and manufacturing have been identified. Due to the use of the majority logic gate as the main building block of logic designs, the probability and impact of a defect affecting this type of element is significant. The effect can be translated into a change of the boolean expression implemented by the gate. QCA Approximate adders have been proposed for image processing and other applications. This paper analyzes the effect of QCA majority gate defects in the processing of images when using approximate adders. This is done by evaluating the variation in the value of common error distance metrics in the presence of defects. Mitigation of these defects by combining approximate and exact adders and selective introduction of fault-tolerant majority gates in different bits is analyzed. The technique achieves a reduction of around 75% of the average normalized mean error distance (NMED). Specific image-based metrics such as PSNR and SSIM are also evaluated in two different experiments, with an increase of up to 225% and 226% respectively. The increase in area is limited to around 40%., Depto. de Arquitectura de Computadores y Automática, Fac. de Informática, TRUE, pub
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- 2024
31. Andreev quantum dot chains in indium antimonide nanowires
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Wu, Hao and Wu, Hao
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Kitaev chain is a theoretical model of a one-dimensional topological superconductor with Majorana zero modes at the two ends of the chain. Intending to emulate Kitaev chain, we build a tight-binding model of a 3-site quantum dot chain. Simulations of the energy spectrum and transport suggest partial-separated Majorana zero modes localize at two end sites within a narrow parameter window. Theory indicates that the triple-dot states acquire Majorana polarization in the fine-tuned regime (Kitaev regime) when Andreev states in all three dots reach zero-energy in a narrow range of magnetic field. A zero-bias peak extends in magnetic fields would appear. We build a chain of three Andreev quantum dots in a semiconductor InSb nanowire. We observe Andreev bound states in each of the three dots, study their magnetic field and gate voltage dependence, and observe dot-dependent zero-bias conductance peaks in magneto-transport spectroscopy. We interpret zero-bias peaks as Andreev states along the triple-dot chain crossing zero-energy at finite magnetic fields. In our device, transport is dominated by one of the quantum dots in the chain, which has a zero-bias crossing at lower magnetic fields than the other two dots, placing the Kitaev regime with Majorana end modes out of reach. The device geometry is suitable for studying the correlation of two end states with non-local measurements. A hard induced superconducting gap surviving to higher magnetic fields is desired. Devices with greater uniformity or independent control over superconductor-semiconductor coupling should realize the Kitaev chain with a high yield. We characterize hybrid InSb nanowire/Sn shell devices fabricated with in-situ shadow technique and observe a hard induced superconducting gap that persists up to 4T in magnetic field. The two-electron charging effect, a hallmark of charge parity stability, is observed in a small island of Sn/InSb. We also study a double quantum dot in a hybrid InAs nanowire/Al shell dev
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- 2024
32. Towards scalable cryogenic quantum dot biasing using memristor-based DC sources
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Mouny, Pierre-Antoine, Dawant, Raphaël, Dufour, Patrick, Valdenaire, Matthieu, Ecoffey, Serge, Pioro-Ladrière, Michel, Beillard, Yann, Drouin, Dominique, Mouny, Pierre-Antoine, Dawant, Raphaël, Dufour, Patrick, Valdenaire, Matthieu, Ecoffey, Serge, Pioro-Ladrière, Michel, Beillard, Yann, and Drouin, Dominique
- Abstract
Cryogenic memristor-based DC sources offer a promising avenue for in situ biasing of quantum dot arrays. In this study, we present experimental results and discuss the scaling potential for such DC sources. We first demonstrate the operation of a commercial discrete operational amplifier down to 1.2K which is used on the DC source prototype. Then, the tunability of the memristor-based DC source is validated by performing several 250mV-DC sweeps with a resolution of 10mV at room temperature and at 1.2K. Additionally, the DC source prototype exhibits a limited output drift of $\approx1\mathrm{\mu Vs^{-1}}$ at 1.2K. This showcases the potential of memristor-based DC sources for quantum dot biasing. Limitations in power consumption and voltage resolution using discrete components highlight the need for a fully integrated and scalable complementary metal-oxide-semiconductor-based (CMOS-based) approach. To address this, we propose to monolithically co-integrate emerging non-volatile memories (eNVMs) and 65nm CMOS circuitry. Simulations reveal a reduction in power consumption, down to $\mathrm{10\mu W}$ per DC source and in footprint. This allows for the integration of up to one million eNVM-based DC sources at the 4.2K stage of a dilution fridge, paving the way for near term large-scale quantum computing applications.
- Published
- 2024
33. Epitaxially regrown quantum dot photonic crystal surface emitting lasers
- Author
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Kyaw, Aye S. M., King, Ben C., McKenzie, Adam F., Bian, Zijun, Kim, Daehyun, Gerrard, Neil D., Nishi, Kenichi, Takemasa, Keizo, Sugawara, Mitsuru, Childs, David T. D., Hill, Calum H., Taylor, Richard J. E., Hogg, Richard A., Kyaw, Aye S. M., King, Ben C., McKenzie, Adam F., Bian, Zijun, Kim, Daehyun, Gerrard, Neil D., Nishi, Kenichi, Takemasa, Keizo, Sugawara, Mitsuru, Childs, David T. D., Hill, Calum H., Taylor, Richard J. E., and Hogg, Richard A.
- Abstract
Quantum dot-based epitaxially regrown photonic crystal surface emitting lasers are demonstrated at room temperature. The GaAs-based devices, which are monolithically integrated on the same wafer, exhibit ground state lasing at ∼1230 nm and excited state lasing at ∼1140 nm with threshold current densities of 0.69 and 1.05 kA/cm2, respectively.
- Published
- 2024
34. Monolithic integration of quantum dot lasers on 300 mm silicon photonic wafers
- Author
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Feng, Kaiyin, Bowers, John E1, Feng, Kaiyin, Feng, Kaiyin, Bowers, John E1, and Feng, Kaiyin
- Abstract
Rapid development of the Si photonics industry and its applications in data communication calls for the making of on-chip light sources integrated on the Silicon-on-Insulator (SOI) platform for mass production. Monolithic integration of III-V lasers, especially quantum dot (QD) lasers has gained increasing attention as a key technology to realize efficient, cost-effective, industrial-scale integration of light sources for Si photonics. In this thesis, we demonstrate for the first time, QD lasers grown and fabricated for electrically pumped lasing both on a planar template and in-pocket-template on 300 mm Si wafers. O-band edge-emitting in-pocket lasers are fabricated on Si with robust performance of continuous wave lasing up to 60 \textdegree C, a maximum double-sided output power of 124.8 mW at 20 °C and high fabrication yield. We also demonstrate for the first time, on-chip etched-facet lasers directly butt-coupled to SiN waveguides made on a 300-mm scale foundry-processed Si photonics wafer, characterized with fiber-coupling from on-chip edge couplers at waveguide output. Process developments addressing issues such as polycrystal deposition on surface, high aspect-ratio pocket geometry, and complications on growth interface affecting coupling are established. Perspectives on scaling this QD laser process on a 300 mm scale in a Si photonics foundry is also discussed, including remaining challenges of improving laser performance and yield, and prospects on the implementation of fully monolithic integration with a III-V/Si co-processing foundry.
- Published
- 2024
35. Explainable Classification Techniques for Quantum Dot Device Measurements
- Author
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Schug, Daniel, Kovach, Tyler J., Wolfe, M. A., Benson, Jared, Park, Sanghyeok, Dodson, J. P., Corrigan, J., Eriksson, M. A., Zwolak, Justyna P., Schug, Daniel, Kovach, Tyler J., Wolfe, M. A., Benson, Jared, Park, Sanghyeok, Dodson, J. P., Corrigan, J., Eriksson, M. A., and Zwolak, Justyna P.
- Abstract
In the physical sciences, there is an increased need for robust feature representations of image data: image acquisition, in the generalized sense of two-dimensional data, is now widespread across a large number of fields, including quantum information science, which we consider here. While traditional image features are widely utilized in such cases, their use is rapidly being supplanted by Neural Network-based techniques that often sacrifice explainability in exchange for high accuracy. To ameliorate this trade-off, we propose a synthetic data-based technique that results in explainable features. We show, using Explainable Boosting Machines (EBMs), that this method offers superior explainability without sacrificing accuracy. Specifically, we show that there is a meaningful benefit to this technique in the context of quantum dot tuning, where human intervention is necessary at the current stage of development., Comment: 5 pages, 3 figures
- Published
- 2024
36. Enhancing Small Object Encoding in Deep Neural Networks: Introducing Fast&Focused-Net with Volume-wise Dot Product Layer
- Author
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Tofik, Ali, Pratim, Roy Partha, Tofik, Ali, and Pratim, Roy Partha
- Abstract
In this paper, we introduce Fast&Focused-Net, a novel deep neural network architecture tailored for efficiently encoding small objects into fixed-length feature vectors. Contrary to conventional Convolutional Neural Networks (CNNs), Fast&Focused-Net employs a series of our newly proposed layer, the Volume-wise Dot Product (VDP) layer, designed to address several inherent limitations of CNNs. Specifically, CNNs often exhibit a smaller effective receptive field than their theoretical counterparts, limiting their vision span. Additionally, the initial layers in CNNs produce low-dimensional feature vectors, presenting a bottleneck for subsequent learning. Lastly, the computational overhead of CNNs, particularly in capturing diverse image regions by parameter sharing, is significantly high. The VDP layer, at the heart of Fast&Focused-Net, aims to remedy these issues by efficiently covering the entire image patch information with reduced computational demand. Experimental results demonstrate the prowess of Fast&Focused-Net in a variety of applications. For small object classification tasks, our network outperformed state-of-the-art methods on datasets such as CIFAR-10, CIFAR-100, STL-10, SVHN-Cropped, and Fashion-MNIST. In the context of larger image classification, when combined with a transformer encoder (ViT), Fast&Focused-Net produced competitive results for OpenImages V6, ImageNet-1K, and Places365 datasets. Moreover, the same combination showcased unparalleled performance in text recognition tasks across SVT, IC15, SVTP, and HOST datasets. This paper presents the architecture, the underlying motivation, and extensive empirical evidence suggesting that Fast&Focused-Net is a promising direction for efficient and focused deep learning.
- Published
- 2024
37. Surface Topological Plexcitons: Strong Coupling in a Bi2Se3 Topological Insulator Nanoparticle-Quantum Dot Molecule
- Author
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Kountouris, George, Yannopapas, Vassilios, Kountouris, George, and Yannopapas, Vassilios
- Abstract
Strong coupling of quantum states with electromagnetic modes of topological matter offer an interesting platform for the exploration of new physics and applications. In this work, we report a novel hybrid mode, a surface topological plexciton, arising from strong coupling between the surface topological plasmon mode of a (Formula presented.) topological insulator nanoparticle and the exciton of a two-level quantum emitter. We study the power absorption spectrum of the system by working within the dipole and rotating-wave approximations, using a density matrix approach for the emitter, and a classical dielectric-function approach for the topological-insulator nanoparticle. We show that a Rabi-type splitting can appear in the spectrum suggesting the presence of strong coupling. Furthermore, we study the dependence of the splitting on the separation of the two nanoparticles as well as the dipole moment of the quantum emitter. These results can be useful for exploring exotic phases of matter, furthering research in topological insulator plasmonics, as well as for applications in the far-infrared and quantum computing.
- Published
- 2024
38. FedDr+: Stabilizing Dot-regression with Global Feature Distillation for Federated Learning
- Author
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Kim, Seongyoon, Jeong, Minchan, Kim, Sungnyun, Cho, Sungwoo, Ahn, Sumyeong, Yun, Se-Young, Kim, Seongyoon, Jeong, Minchan, Kim, Sungnyun, Cho, Sungwoo, Ahn, Sumyeong, and Yun, Se-Young
- Abstract
Federated Learning (FL) has emerged as a pivotal framework for the development of effective global models (global FL) or personalized models (personalized FL) across clients with heterogeneous, non-iid data distribution. A key challenge in FL is client drift, where data heterogeneity impedes the aggregation of scattered knowledge. Recent studies have tackled the client drift issue by identifying significant divergence in the last classifier layer. To mitigate this divergence, strategies such as freezing the classifier weights and aligning the feature extractor accordingly have proven effective. Although the local alignment between classifier and feature extractor has been studied as a crucial factor in FL, we observe that it may lead the model to overemphasize the observed classes within each client. Thus, our objectives are twofold: (1) enhancing local alignment while (2) preserving the representation of unseen class samples. This approach aims to effectively integrate knowledge from individual clients, thereby improving performance for both global and personalized FL. To achieve this, we introduce a novel algorithm named FedDr+, which empowers local model alignment using dot-regression loss. FedDr+ freezes the classifier as a simplex ETF to align the features and improves aggregated global models by employing a feature distillation mechanism to retain information about unseen/missing classes. Consequently, we provide empirical evidence demonstrating that our algorithm surpasses existing methods that use a frozen classifier to boost alignment across the diverse distribution.
- Published
- 2024
39. Implementing and Optimizing the Scaled Dot-Product Attention on Streaming Dataflow
- Author
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Sohn, Gina, Zhang, Nathan, Olukotun, Kunle, Sohn, Gina, Zhang, Nathan, and Olukotun, Kunle
- Abstract
Transformer models serve as the backbone of many state-ofthe-art language models, and most use the scaled dot-product attention (SDPA) mechanism to capture relationships between tokens. However, the straightforward implementation of SDPA has quadratic compute and memory complexity with respect to the sequence length. On processor architectures such as GPUs and TPUs, there is a robust body of prior work. However, little work has been performed on non-processor architectures.In this work, we show how the architecture and execution model of Streaming Dataflow Accelerators can help tackle this challenge. We first define abstract hardware that adopts a streaming execution model, and we implement a cycle-accurate simulator of the abstract hardware using the Dataflow Abstract Machine simulation framework. Second, we implement the naive SDPA algorithm on this abstract hardware and show it requires linear (O(N)) intermediate memory. Third, we then modify the naive algorithm, taking inspiration from prior processor-oriented works, by reordering the multiplication and division operations. Finally, we map the modified algorithm to abstract hardware, and confirm that the implementation computes SDPA at full throughput while only using a constant amount (O(1)) of intermediate memory., Comment: 4 pages, 3 figures
- Published
- 2024
40. Active region doping strategies in O-band InAs/GaAs quantum-dot lasers
- Author
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Jarvis, Lydia
- Subjects
QC Physics - Abstract
Three techniques for improving gain in InAs quantum dot lasers are examined. Silicon photonics is a promising solution for meeting increasing global data bandwidth demands. However, silicon itself is a poor emitter due to its indirect bandgap. One potential candidate for light sources for on-chip devices is the monolithic growth of III-V quantum dot materials onto silicon, however, III-V quantum dot materials exhibit reduced gain due to the differences in the population of electron and hole states and ultimately because of the difference in electron and hole effective masses. P-type modulation doping is a well-established strategy for improving gain in InAs quantum dot lasers on both native GaAs and silicon substrates. The doping density and positioning is optimised for a given wafer design, and ground state lasing at room temperature for a 400um lasing cavity is demonstrated, in addition to reduced sensitivity of threshold current to temperature. Optimized p-type modulation doping is compared to a relatively new approach to enhancing gain - direct n-type doping of the quantum dots. It is found to improve the gain in low loss operation, unlike p-type modulation doping. However, direct n-type doping detrimentally showed increased threshold current dependence compared with p-type modulation doping and decreased the maximum temperature at which ground state lasing could be attained. A novel third method is investigated in which both p-type modulation doping and direct n-type doping are applied to a device simultaneously, referred to as co-doping. Co-doping reduced the threshold current density from 245 A/cm^2 to 132 A/cm^2 at 27C and 731 A/cm^2 to 312 A/cm^2 at 97C, compared to undoped devices. The reduction was greater than for either individual doping strategy alone. Co-doping also retained the beneficial reduction in the sensitivity of the threshold current density to temperature provided by the p-type modulation doping.
- Published
- 2022
41. Gate-based sensing of silicon quantum dot devices towards 2D scaling
- Author
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Duan, Jingyu
- Abstract
This thesis focuses on using the radio-frequency reflectometry technique for dispersive gate sensing of foundry fabricated silicon nanowire quantum dot devices. I will attempt to answer three questions relating to the scalability of these devices. How do electron and hole spin qubits perform in silicon quantum dots? How do we implement and distribute the placement of dispersive gate sensors in scaled-up quantum dot arrays? And how does a single dopant in the silicon channel affect the gate-defined quantum dot? First, I investigate the difference between electron and hole quantum dots in an ambipolar nanowire device which successfully demonstrated reconfigurable single and double electron and hole quantum dots in the same crystalline environment. I further investigate the effective bath temperature of two-dimensional electron gas and two-dimensional hole gas by performing the thermometry experiment on the same type of device. Secondly, I demonstrate a two-dimensional quantum dot array enabled by a floating gate architecture between silicon nanowires. An analytical model is developed to study the capacitive coupling between remote quantum dots over different distances. Coupling strength under different qubit encodings is also discussed to show the best implementation for neighbour silicon nanowires. Finally, the in-situ dispersive gate sensing allows the measurement of the inter-dot transition between the bismuth donor-dot system. The novel implementation with bismuth donor can open up the possibility of a hybrid singlet-triplet qubit or transferring a coherent spin state between the quantum dot and the donor.
- Published
- 2022
42. One‐Dimensionally Arranged Quantum‐Dot Superstructures Guided by a Supramolecular Polymer Template
- Author
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20802226, 20372724, Yamauchi, Mitsuaki, Nakatsukasa, Kanako, Kubo, Naoki, Yamada, Hiroko, Masuo, Sadahiro, 20802226, 20372724, Yamauchi, Mitsuaki, Nakatsukasa, Kanako, Kubo, Naoki, Yamada, Hiroko, and Masuo, Sadahiro
- Abstract
Colloidal quantum dots (QDs) exhibit important photophysical properties, such as long-range energy diffusion, miniband formation, and collective photoluminescence, when aggregated into well-defined superstructures, such as three-dimensional (3D) and two-dimensional (2D) superlattices. However, the construction of one-dimensional (1D) QD superstructures, which have a simpler arrangement, is challenging; therefore, the photophysical properties of 1D-arranged QDs have not been studied previously. Herein, we report a versatile strategy to obtain 1D-arranged QDs using a supramolecular polymer (SP) template. The SP is composed of self-assembling cholesterol derivatives containing two amide groups for hydrogen bonding and a carboxyl group as an adhesion moiety on the QDs. Upon mixing the SP and dispersed QDs in low-polarity solvents, the QDs self-adhered to the SP and self-arranged into 1D superstructures through van der Waals interactions between the surface organic ligands of the QDs, as confirmed by transmission electron microscopy. Furthermore, we revealed efficient photoinduced fluorescence resonance energy transfer between the 1D-arranged QDs by an in-depth analysis of the emission spectra and decay curves.
- Published
- 2024
43. Possible charge ordering and anomalous transport in graphene/graphene quantum dot heterostructure
- Author
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Gómez Pérez, Inmaculada Jénnifer, Roy, Rajarshi, Holec, David, Michal, Lukáš, Hemzal, Dušan, Sarkar, Saikat, Gundam, Sandeep Kumar, Nečas, David, Dhankhar, Meena, Kaushik, Preeti, Zajickova, Lenka, Gómez Pérez, Inmaculada Jénnifer, Roy, Rajarshi, Holec, David, Michal, Lukáš, Hemzal, Dušan, Sarkar, Saikat, Gundam, Sandeep Kumar, Nečas, David, Dhankhar, Meena, Kaushik, Preeti, and Zajickova, Lenka
- Abstract
[Abstract] Observations of superconductivity and charge density waves (CDW) in graphene have been elusive thus far due to weak electron–phonon coupling (EPC) interactions. Here, we report a unique observation of anomalous transport and multiple charge ordering phases at high temperatures (T1 ∼ 213K, T2 ∼ 325K) in a 0D−2D van der Waals (vdW) heterostructure comprising of single layer graphene (SLG) and functionalized (amine) graphene quantum dots (GQD). The presence of functionalized GQD contributed to charge transfer with shifting of the Dirac point ∼ 0.05 eV above the Fermi level (ab initio simulations) and carrier density n ∼ −0.3 × 1012 cm−2 confirming p-doping in SLG and two-fold increase in EPC interaction was achieved. Moreover, we elucidate the interplay between electron–electron and electron–phonon interactions to substantiate high temperature EPC driven charge ordering in the heterostructure through analyses of magnetotransport and weak anti-localization (WAL) ramework. Our results provide impetus to investigate strongly correlated phenomena such as CDW and superconducting phase transitions in novel graphene based heterostructures.
- Published
- 2024
44. Elongated quantum dot as a distributed charge sensor
- Author
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Patomäki, S. M., Williams, J., Berritta, F., Lainé, C., Fogarty, M. A., Leon, R. C. C., Jussot, J., Kubicek, S., Chatterjee, A., Govoreanu, B., Kuemmeth, F., Morton, J. J. L., Gonzalez-zalba, M. F., Patomäki, S. M., Williams, J., Berritta, F., Lainé, C., Fogarty, M. A., Leon, R. C. C., Jussot, J., Kubicek, S., Chatterjee, A., Govoreanu, B., Kuemmeth, F., Morton, J. J. L., and Gonzalez-zalba, M. F.
- Published
- 2024
45. Quantum dot coupled to a suspended-beam mechanical resonator:From the unresolved- to the resolved-sideband regime
- Author
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Spinnler, Clemens, Nguyen, Giang N., Wang, Ying, Erbe, Marcel, Javadi, Alisa, Zhai, Liang, Scholz, Sven, Wieck, Andreas D., Ludwig, Arne, Lodahl, Peter, Midolo, Leonardo, Warburton, Richard J., Spinnler, Clemens, Nguyen, Giang N., Wang, Ying, Erbe, Marcel, Javadi, Alisa, Zhai, Liang, Scholz, Sven, Wieck, Andreas D., Ludwig, Arne, Lodahl, Peter, Midolo, Leonardo, and Warburton, Richard J.
- Published
- 2024
46. Non-Abelian Holonomy of Majorana Zero Modes Coupled to a Chaotic Quantum Dot
- Author
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Geier, Max, Krøjer, Svend, Von Oppen, Felix, Marcus, Charles M., Flensberg, Karsten, Brouwer, Piet W., Geier, Max, Krøjer, Svend, Von Oppen, Felix, Marcus, Charles M., Flensberg, Karsten, and Brouwer, Piet W.
- Published
- 2024
47. Majorana Qubits and Non-Abelian Physics in Quantum Dot–Based Minimal Kitaev Chains
- Author
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Tsintzis, Athanasios, Souto, Rubén Seoane, Flensberg, Karsten, Danon, Jeroen, Leijnse, Martin, Tsintzis, Athanasios, Souto, Rubén Seoane, Flensberg, Karsten, Danon, Jeroen, and Leijnse, Martin
- Published
- 2024
48. Exciton Transport in a Germanium Quantum Dot Ladder
- Author
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Hsiao, T.-k., Cova Fariña, P., Oosterhout, S. D., Jirovec, D., Zhang, X., Van Diepen, C. J., Lawrie, W. I. L., Wang, C.-a., Sammak, A., Scappucci, G., Veldhorst, M., Demler, E., Vandersypen, L. M. K., Hsiao, T.-k., Cova Fariña, P., Oosterhout, S. D., Jirovec, D., Zhang, X., Van Diepen, C. J., Lawrie, W. I. L., Wang, C.-a., Sammak, A., Scappucci, G., Veldhorst, M., Demler, E., and Vandersypen, L. M. K.
- Published
- 2024
49. Possible charge ordering and anomalous transport in graphene/graphene quantum dot heterostructure
- Author
-
Roy, Rajarshi, Holec, David, Michal, Lukáš, Hemzal, Dušan, Sarkar, Saikat, Sandeep Kumar, Gundam, Nečas, David, Dhankhar, Meena, Kaushik, Preeti, Jénnifer Gómez, I., Zajíčková, Lenka, Roy, Rajarshi, Holec, David, Michal, Lukáš, Hemzal, Dušan, Sarkar, Saikat, Sandeep Kumar, Gundam, Nečas, David, Dhankhar, Meena, Kaushik, Preeti, Jénnifer Gómez, I., and Zajíčková, Lenka
- Abstract
Observations of superconductivity and charge density waves (CDW) in graphene have been elusive thus far due to weak electron-phonon coupling (EPC) interactions. Here, we report a unique observation of anomalous transport and multiple charge ordering phases at high temperatures ( T1 ∼ 213K , T2 ∼ 325K ) in a 0D−2D van der Waals (vdW) heterostructure comprising of single layer graphene (SLG) and functionalized (amine) graphene quantum dots (GQD). The presence of functionalized GQD contributed to charge transfer with shifting of the Dirac point ∼ 0.05 eV above the Fermi level (ab initio simulations) and carrier density n ∼ − 0.3 × 1012 cm−2 confirming p-doping in SLG and two-fold increase in EPC interaction was achieved. Moreover, we elucidate the interplay between electron-electron and electron-phonon interactions to substantiate high temperature EPC driven charge ordering in the heterostructure through analyses of magnetotransport and weak anti-localization (WAL) framework. Our results provide impetus to investigate strongly correlated phenomena such as CDW and superconducting phase transitions in novel graphene based heterostructures.
- Published
- 2024
50. Let's Think Dot by Dot: Hidden Computation in Transformer Language Models
- Author
-
Pfau, Jacob, Merrill, William, Bowman, Samuel R., Pfau, Jacob, Merrill, William, and Bowman, Samuel R.
- Abstract
Chain-of-thought responses from language models improve performance across most benchmarks. However, it remains unclear to what extent these performance gains can be attributed to human-like task decomposition or simply the greater computation that additional tokens allow. We show that transformers can use meaningless filler tokens (e.g., '......') in place of a chain of thought to solve two hard algorithmic tasks they could not solve when responding without intermediate tokens. However, we find empirically that learning to use filler tokens is difficult and requires specific, dense supervision to converge. We also provide a theoretical characterization of the class of problems where filler tokens are useful in terms of the quantifier depth of a first-order formula. For problems satisfying this characterization, chain-of-thought tokens need not provide information about the intermediate computational steps involved in multi-token computations. In summary, our results show that additional tokens can provide computational benefits independent of token choice. The fact that intermediate tokens can act as filler tokens raises concerns about large language models engaging in unauditable, hidden computations that are increasingly detached from the observed chain-of-thought tokens., Comment: 17 pages, 10 figures
- Published
- 2024
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