Dot System Research Articles

Local Activity in a Self‐Assembled Quantum Dot System

AbstractResearch and development of memristor‐based neuromorphic networks has entered the stage of large‐scale application. However, the understanding of the adopted memristors is still vague, meaning a thorough study of their local activity is urgently necessary. Here, an electrode tip is created to focus the electrical field on the active locality, where the NbO quantum dot (QD) self‐assembles in the middle of the Nb‐doped AlNO film. The QD size can fluctuate under an appropriately controlled electron beam or electrical field, suggesting reversible nucleation behavior. The QD system periodically pulses when the input is enhanced to a co‐tunneling threshold or to one that activates the oscillation of the QD size. These two mechanisms are attributed to the local activity accounting for the information‐energy conversion of the QD system. This study presents a more precise and low energy‐consumption approach for neuromorphic computing by manipulating the local activity.

Classical Force Field Parameters for InP and InAs Quantum Dots with Various Surface Passivations.

Classical molecular dynamics (MD) simulations on realistic colloidal quantum dot (QD) systems are often hampered by missing force field (FF) parameters for an accurate description of the QD-ligand interface. However, such calculations are of major interest, specifically for studying the surface chemistry of colloidal nanocrystals. In this work, we have utilized a previously published stochastic optimization algorithm to obtain FF parameters for InP and InAs QDs capped by Cl, amine, carboxylate, and thiolate ligands. Our FF parameters are interfaced with well-established FFs for organic molecules, allowing for the simulation of InP and InAs QDs with a broad range of organic ligands in explicit apolar solvents. The quality of our FF parameters was assessed by comparing properties of the classical MD simulations with ab initio MD simulations and experimental and theoretical values from the literature.

Transient dynamics of subradiance and superradiance in open optical ensembles

We introduce a computational Maxwell-Bloch framework for investigating out-of-equilibrium optical emitters in open systems. To do so, we compute the pulse-induced dynamics of each emitter from fundamental light-matter interactions and self-consistently calculate their radiative coupling, including phase inhomogeneity from propagation effects. This semiclassical framework is applied to open quantum dots systems with different densities and dipolar coupling. We observe signatures of superradiant behavior, such as directionality and faster decay, as well as subradiant emission. We compare and discuss the computed light emission obtained with our method and a Master equation approach. Our framework enables quantitative investigations of large optical ensembles in the time domain and could be used to design new systems with enhanced superradiant and subradiant properties.

Photoinduced Modulation of the Dielectric Permittivity in a System of Interacting Quantum Dots in an External Electric Field

Photoinduced Modulation of the Dielectric Permittivity in a System of Interacting Quantum Dots in an External Electric Field

Realistic Protocol to Measure Entanglement at Finite Temperatures.

It is desirable to relate entanglement of many-body systems to measurable observables. In systems with a conserved charge, it was recently shown that the number entanglement entropy (NEE)-i.e., the entropy change due to an unselective subsystem charge measurement-is an entanglement monotone. Here we derive finite-temperature equilibrium relations between Rényi moments of the NEE, and multipoint charge correlations. These relations are exemplified in quantum dot systems where the desired charge correlations can be measured via a nearby quantum point contact. In quantum dots recently realizing the multichannel Kondo effect we show that the NEE has a nontrivial universal temperature dependence which is now accessible using the proposed methods.

Energy shift and subharmonics induced by nonlinearity in a quantum dot system

The presence of anticrossings induced by coupling between two states causes curvature in energy levels, yielding a nonlinearity in the quantum system. When the system is driven back and forth along the bending energy levels, subharmonic transitions and energy shifts can be observed, which would cause a significant influence as the system is applied to quantum computing. In this paper, we study a longitudinally driven singlet-triplet (ST) system in a double quantum dot (DQD) system, and illustrate the consequences of nonlinearity by driving the system close to the anticrossings. We provide a straightforward theory to quantitatively describe the energy shift and subharmonics caused by nonlinearity, and find good agreement between our theoretical result and the numerical simulation. Our results reveal the existence of nonlinearity in the vicinity of anticrossings and provide a direct way of analytically assessing its impact, which can be applied to other quantum systems without excessive labor.

Energetics of Microwaves Probed by Double Quantum Dot Absorption.

We explore the energetics of microwaves interacting with a double quantum dot photodiode and show wave-particle aspects in photon-assisted tunneling. The experiments show that the single-photon energy sets the relevant absorption energy in a weak-drive limit, which contrasts the strong-drive limit where the wave amplitude determines the relevant-energy scale and opens up microwave-induced bias triangles. The threshold condition between these two regimes is set by the fine-structure constant of the system. The energetics are determined here with the detuning conditions of the double dot system and stopping-potential measurements that constitute a microwave version of the photoelectric effect.

Effect of Induced Transition on the Quantum Entanglement and Coherence in Two‐Coupled Double Quantum Dot System

AbstractStudying quantum properties in solid‐state systems is a significant avenue for research. In this scenario, double quantum dots appear as a versatile platform for technological breakthroughs in quantum computation and nanotechnology. This work inspects the thermal entanglement and quantum coherence in two‐coupled DODs, where the system is exposed to an external stimulus that induces an electronic transition within each subsystem. The results show that the introduction of external stimulus induces a quantum level crossing that relies upon the Coulomb potential changing the degree of quantum entanglement and coherence of the system. Thus, the quantum properties of the system can be tuned by changing the transition frequency, leading to the enhancement of its quantum properties.

Interference effects in coupled triple quantum dot systems

Electronic transport through a coupled triple quantum dot (TQD) system is theoretically studied using Equilibrium Green’s function approach. The TQD system is systematically investigated for T-shape configuration and triangular shape configuration. T-shape (triangular shape) configuration corresponds to the TQD structure in which two quantum dots (QD)s are connected to the left and right leads in series and third one is side coupled to the right one (both) the QDs. In the electronic transmission spectrum of T-shape configuration, it is found that an antiresonance peak occurs at the QDs energy level and width of the peak increases with the increase in the tunnel coupling of the side coupled QD. Further, an asymmetric Fano lineshape is also observed while investigating transition from the T-shape to the triangular shape configuration. Interestingly, this Fano peak is found to occur when side coupled QD is weakly coupled to both the serially coupled QDs and its appearance becomes more prominent when the side coupled QD is symmetrically coupled to both the QDs. Both these effects reveal quantum interference effects that take place between discrete states and the continuum in electron transport through multiple channels in T-shape and triangular shape geometries.

Dynamics of Superconducting Correlations Induced by Hopping in Serial Double Quantum Dot System

Dynamics of Superconducting Correlations Induced by Hopping in Serial Double Quantum Dot System

Optimal thermoelectric induced by Cooper pair splitting

We study the optimal output power and efficiency of the thermoelectric induced by Cooper pair splitting(CPS). Due to its particular properties such as additional electron injection to the Quantum Dots system, Cooper pair splitting has been regarded as a powerful and available candidate of quantum heat engine. It is well known that elastic cotunnelling process coexist with CPS and several parameters such as temperature difference, bias voltage, Coulomb interaction. Which is most important is one of the key problems to determine the performance of the heat engine. We show the parametric dependence of the output power and efficiency and find the optimal performance of this heat engine with CPS through genetic algorithm.

Variable and Orbital-Dependent Spin-Orbit Field Orientations in an InSb Double Quantum Dot Characterized via Dispersive Gate Sensing

Utilizing dispersive gate sensing (DGS), we investigate the spin-orbit field (${\mathbf{B}}_{\mathrm{SO}}$) orientation in a many-electron double quantum dot (DQD) defined in an $\mathrm{In}\mathrm{Sb}$ nanowire. While characterizing the interdot tunnel couplings, we find the measured dispersive signal depends on the electron-charge occupancy, as well as on the amplitude and orientation of the external magnetic field. The dispersive signal is mostly insensitive to the external field orientation when a DQD is occupied by a total odd number of electrons. For a DQD occupied by a total even number of electrons, the dispersive signal is reduced when the finite external magnetic field aligns with the effective ${\mathbf{B}}_{\mathrm{SO}}$ orientation. This fact enables the identification of ${\mathbf{B}}_{\mathrm{SO}}$ orientations for different DQD electron occupancies. The ${\mathbf{B}}_{\mathrm{SO}}$ orientation varies drastically between charge transitions, and is generally neither perpendicular to the nanowire nor in the chip plane. Moreover, ${\mathbf{B}}_{\mathrm{SO}}$ is similar for pairs of transitions involving the same valence orbital, and varies between such pairs. Our work demonstrates the practicality of DGS in characterizing spin-orbit interactions in quantum dot systems, without requiring any current flow through the device.

Multiple steady states and dark states induced by nonlocal dissipation in a double quantum dot

Both multiple steady states and dark states have potential applications in the quantum information processing in the presence of dissipation. Here, we propose to implement multiple steady states and dark states in a double quantum dot (DQD) system using quantum reservoir engineering. By coupling the DQD to shared reservoirs, multiple steady states of both four- and two-fold degeneracy can be achieved for specific parameters. It is proved that the occurrence of such multiple steady states is attributed to the strong symmetry of the Lindblad master equation. The multiple steady states can be well revealed by the occupation number of the DQD, which exhibits a discontinuity at the strong-symmetric points and changes drastically in the vicinities of these points. In the regime of unique steady state, the system can be stabilized to a pure state, dubbed dark state, with intact coherence in spite of the dissipation. Our work shows that a variety of novel steady states can be implemented in the DQD system, which paves the way for engineering multiple steady states and dark states in the DQD system.

Attitudes toward the Integration of Radiographers into the First-Line Interpretation of Imaging Using the Red Dot System.

The red dot system uses expertise in the identification of anomalies to assist radiologists in distinguishing radiological abnormalities and managing them before the radiologist report is sent. This is a small step on the road to greater role development for radiographers. This practice has existed for more than 20 years in the UK. Today, it is only the UK seeking to legislate radiographer reports. The aim of this paper is to put focus on this issue, determine whether radiographer reports are necessary, and explore whether there are any benefits that can be highlighted to encourage health authorities worldwide to allow radiographers to write clinical reports. Additionally, this study was conducted to evaluate the role of radiographers (non-radiologists) in medical image interpretation, using 95 samples that were collected randomly and a representative sample of radiographers and radiologists of both genders. The SPSS program was used for the statistical analysis of the samples and to scientifically explain the results. We found that radiologists have no objections to the participation of radiographers in diagnosis assistance, interpretation, and clinical reporting through the red dot system. Therefore, there was support for the future implementation of such a system in health care.

Effect of the number of quantum dots on transport properties of multiple quantum dot systems in T-shaped topology

Effect of the number of quantum dots on transport properties of multiple quantum dot systems in T-shaped topology

Beneficial Intrinsic Hole Trapping and Its Amplitude Variation in a Highly Photoluminescent Toxic-Metal-Free Quantum Dot.

Intrinsic hole trapping as well as hole detrapping have not been observed for any quantum dot (QD) or perovskite nanocrystal (PNC) system. Moreover, amplitude variation of intrinsic hole trapping (or detrapping) has not been reported at all for any QD or PNC system. However, for a CuInS2-based core/alloy-shell (CAS) QD system, (a) both intrinsic hole trapping and detrapping have been observed and (b) very significant amplitude variations of hole trapping (∼16 to ∼42%) and hole detrapping (∼44 to 23%) have been observed. Unlike detrimental electron trapping, hole trapping has been shown to be beneficial, having a direct correlation toward increasing PLQY to 96%. Simultaneous electron and hole trapping has been shown to be quite beneficial for the CuInS2-based CAS QD system leading to the longest ON time (∼130 s) for which a nontoxic metal-based QD remains only in the ON-state without blinking.

Study of quantum speed limit of of transport process of single quantum dot system in dissipative environment

We theoretically study the quantum speed limit (QSL) of the single dot system in dissipative environment based on quantum dot transport theory and Bures angle metric method. The theoretical results show that in the dissipative environment, different tunneling probabilities have different effects. The increase of left tunneling probability has a weak effect on the accelerating capability of the system, due to the Coulomb blocking effect and quantum coherence. On the other hand, the right tunneling probability has a significant influence on the accelerating capability of the system, the accelerating capability is promoted with the increase of right tunneling probability because of the effect of channel blocking and co-tunneling. The increase of energy displacement promotes the accelerating capability of the system and changes the oscillation frequency of the system, owing to its taking longer time for the system to evolve to a target state. The effect of the relaxation rate for the system's accelerating capability is not monotonic, there is an interesting turning point due to the change of electron layout number. When the relaxation rate is less than this point, the accelerating capability of the system will oscillate. When the relaxation rate is higher than this point, the change of accelerating capability is monotonically suppressed by the relaxation rate. In general, the increase of the relaxation rate weakens the acceleration capability of the system. Our results provide theoretical reference for studying the QSL time in a semiconductor device affected by numerous factors.

Quantum dots: experience and prospects of application in analytical systems

The article is of a review nature, in which the dynamics of publication activity is analyzed and the possibilities of using quantum dots to solve various analytical problems are evaluated. The attention is paid to both traditional and relatively rare areas of analytical application of these nanostructures. A brief review of the types, advantages and disadvantages of synthesis methods, the influence of external factors on the band gap and luminescence intensity of inorganic nanosized phosphors, quantum dots of different nature, is presented. The areas of application and the main tasks solved with the use of quantum dots are systematized. Their analytical characteristics, operational properties and ways of regulating them are discussed. An effective way to control the analytical properties of the systems based on quantum dots is a directional change of the affinity for components by varying the nature of the stabilizing or modifying shell. Semiconductor colloidal quantum dots coated with a larger bandgap shell were selected for analytical use as the most commonly used systems due to their good photostability and fluorescence quantum yield. The advantages and disadvantages of other types of shells, as well as ways of modifying them, are shown. Solutions for organic analysis and medical diagnostics are considered. Systems of quantum dots used as biosensors with various guiding agents are considered, and their properties, advantages and disadvantages compared. Little studied issues and solutions in the direction of using quantum dots for developing sensor systems and their use for non-invasive analysis of living systems based on the results of detection of volatile organic compounds are identified.

On Noise-Sensitive Automatic Tuning of Gate-Defined Sensor Dots

In gate-defined quantum dot systems, the conductance change of electrostatically coupled sensor dots allows the observation of the quantum dots' charge and spin states. Therefore, the sensor dots must be optimally sensitive to changes in its electrostatic environment. A series of conductance measurements varying the two sensor-dot-forming barrier gate voltages serve to tune the dot into a corresponding operating regime. In this paper, we analyze the noise characteristics of the measured data and define a criterion to identify continuous regions with a sufficient signal-gradient-to-noise ratio. Hence, accurate noise estimation is required when identifying the optimal operating regime. Therefore, we evaluate several existing noise estimators, modify them for 1D data, optimize their parameters, and analyze their quality based on simulated data. The estimator of Chen et al. [1] turns out to be best suited for our application concerning minimally scattering results. Furthermore, using this estimator in an algorithm for flank-of-interest classification in measured data shows the relevance and applicability of our approach.

Double protein directed synthesis of chemically etched sulfur doped quantum dots for signal "on-off-on" sensing of glutathione mediated by copper ions.

In this study, a novel "on-off-on" fluorescent probe was suggested for sensitive and selective assay of glutathione (GSH). The as-fabricated nanoswitch employs a Cu2+-sulfur quantum dot system (SQ-dots/Cu2+). The surface reactivity and water solubility of SQ-dots were improved through capping with egg white and bovine serum albumin proteins. The surface functional groups on the surface of double protein-protected SQ-dots enhanced the interaction with Cu2+ ions, resulting in the aggregation induced quenching of SQ-dots. Addition of GSH, a strong Cu2+ ion chelator, disassembles the large aggregates into relatively smaller ones, restoring the fluorescence emission of SQ-dots. Under optimized conditions, the fluorescence intensity was increased by increasing GSH amounts within the range of 0.13-550 μM with a detection limit (S/N = 3) of 0.04 μM. The SQ-dots/Cu2+ system was successfully applied for the detection of GSH in different matrices such as dietary supplements, human serum, and vegetable extract samples. The as-fabricated probe holds great potential for the synthesis of other functionalized SQ-dots for (bio) sensing.