Coupled Quantum Dots Research Articles

Simultaneous enhancements on emissions from quantum dot and quantum well by Ag nanoparticles for color conversion

Quantum dots (QDs) have been paid much attention on the color conversion for light-emitting diode (LED) in micro-display recently. However, it is hard to achieve high color conversion efficiency in a thin QD layer. In this paper, we fabricated silver nanoparticles (Ag NPs) with radii ranging mostly from 25 to 35 nm on a blue LED with a peak wavelength of 450 nm, then spin-coated QDs with a peak wavelength of 565 nm. Scanning electron microscopy, cathodoluminescence, photoluminescence (PL), and time-resolved PL measurements were performed. The PL emissions from quantum wells (QWs) of blue LED and QDs were enhanced by 10% and 32%, respectively, when the Ag NPs were included. The PL lifetimes of QWs and QDs were reduced by 10 and 6 times, respectively, compared to their initial states. Finite difference time domain software and the perturbation method were used to simulate the PL measurements and variable separation. It was concluded that the coupling of QDs and QWs with localized surface plasmon improves the external quantum efficiency and enhances the spontaneous emission rate in both QWs and QDs. This paper provides a new idea for designing high-efficiency color conversion micro-LED.

Design of a Frequency Multiplier Based on Laterally Coupled Quantum Dots for Optoelectronic Device Applications in the Terahertz Domain: Impact of Inhomogeneous Indium Distribution, Strain, Pressure, Temperature, and Electric Field

Design of a Frequency Multiplier Based on Laterally Coupled Quantum Dots for Optoelectronic Device Applications in the Terahertz Domain: Impact of Inhomogeneous Indium Distribution, Strain, Pressure, Temperature, and Electric Field

Both enhancement and strong coupling of quantum dots on asymmetric Fabry-Perot cavity at room temperature

Abstract The interaction of light and matter is an eternal theme in optics and optoelectronics. Until now, there is almost no report about realization of both strong coupling and enhancement simultaneously. In this study, the angle-resolved photoluminescence spectra of colloidal quantum dots on the surface of SiO2/Si material are investigated. When the PL spectrum peak overlaps with the Fabry–Perot (F-P) mode of SiO2 film, the PL spectrum near emission wavelength of bare colloidal quantum dots splits into two peaks, which is Rabi splitting. Moreover, a huge enhancement factor is obtained for the PL spectra in the short-wavelength region. Both extremely huge enhancement and large Rabi splitting are obtained with colloidal quantum dots coupled low-refractive-index/high-refractive-index dielectric material system.

An Exact Expression for Multidimensional Spectroscopy of a Spin‐Boson Hamiltonian

AbstractMultidimensional coherent spectroscopy is a powerful tool to characterize nonlinear optical response functions. Typically, multidimensional spectra are interpreted via a perturbative framework that straightforwardly provides intuition into the density matrix dynamics that give rise to specific spectral features. When the goal is to characterize system coupling to a thermal bath however, the perturbative formalism becomes unwieldy and yields less intuition. Here, an approach developed by Vagov et al. is extended to provide an exact expression for multidimensional spectra of a spin‐boson Hamiltonian up to arbitrary order of electric field interaction. The utility of this expression is demonstrated by modeling polaron formation and coherent exciton‐phonon coupling in quantum dots, which strongly agree with experiment.

Bright Nonblinking Photoluminescence with Blinking Lifetime from a Nanocavity-Coupled Quantum Dot.

Colloidal quantum dots (QDs) are excellent luminescent nanomaterials for many optoelectronic applications. However, photoluminescence blinking has limited their practical use. Coupling QDs to plasmonic nanostructures shows potential in suppressing blinking. However, the underlying mechanism remains unclear and debated, hampering the development of bright nonblinking dots. Here, by deterministically coupling a QD to a plasmonic nanocavity, we clarify the mechanism and demonstrate unprecedented single-QD brightness. In particular, we report for the first time that a blinking QD could obtain nonblinking photoluminescence with a blinking lifetime through coupling to the nanocavity. We show that the plasmon-enhanced radiative decay outcompetes the nonradiative Auger process, enabling similar quantum yields for charged and neutral excitons in the same dot. Meanwhile, we demonstrate a record photon detection rate of 17 MHz from a colloidal QD, indicating an experimental photon generation rate of more than 500 MHz. These findings pave the way for ultrabright nonblinking QDs, benefiting diverse QD-based applications.

Multiphoton emission of single CdZnSe/ZnS quantum dots coupled with plasmonic Au nanoparticles.

The fluorescence blinking and low multiphoton emission of quantum dots (QDs) have limited their application in lasing, light-emitting diodes, and so on. Coupling of single QDs to plasmonic nanostructures is an effective approach to control the photon properties. Here plasmon-exciton systems including Au nanoparticles and CdZnSe/ZnS QDs were investigated at the single particle level. With the modulation of the local electromagnetic field, the fluorescence intensity of single QDs is increased, accompanied by a significant suppression in blinking behavior, and the lifetime is shortened from 15 ns to 2 ns. Moreover, the second-order photon intensity correlation at zero lag time g2(0) of coupled single QDs is larger than 0.5, indicating an increased probability of multiphoton emission. The enhancement factors of radiative and nonradiative decay rates of QDs coupled with Au nanoparticles are calculated. The sharply increased radiative decay rate can be comparable to the nonradiative Auger rate, leading to dominated multiple exciton radiative recombination with PL intensity enhancement, suppressed blinking, lifetime shortening, and multiphoton emission. The results of the exciton decay dynamics and emission properties of single QDs in this work are helpful in exploring the mechanism of plasmon-exciton interaction and optoelectronic application of single QDs.

Chiral Majorana fermions resonance exchange moudulated by quantum dot coupling strength

We study the resonance exchanges of two chiral Majorana fermions in two distinct systems theoretically in this work: one is an isolated Majorana zero mode interacting with complexes formed by two chiral Majorana fermions and a Majorana zero mode, and the other involves isolated quantum dots that are coupled to a system composed of Majorana fermions and a quantum dot. Our research results reveal that both of these coupled systems can facilitate the effective transmissions of the two chiral Majorana fermions as <inline-formula><tex-math id="M1">\begin{document}$ {\gamma _1} \to - {\gamma _2} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M1.png"/></alternatives></inline-formula>and <inline-formula><tex-math id="M2">\begin{document}$ {\gamma _2} \to - {\gamma _1} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M2.png"/></alternatives></inline-formula>, and the resonant tunneling effects in the two systems are equivalent. Therefore, quantum dots can replace Majorana zero modes to achieve resonant tunneling. In order to observe the resonance exchange of two chiral Majorana fermions with the two quantum dots, a circuit based on anomalous quantum Hall insulator proximity-coupled with s-wave superconductor is proposed as shown in figure. The numerical results indicate that the resonant exchange of chiral Majorana fermions can be modulated by the coupling strength between the two quantum dots, and it is particularly noteworthy that the tunneling process is independent of the superconducting phase. If one of the chiral Majorana fermions undergoes resonance coupling with another quantum dot or Majorana zero mode, an additional negative sign is obtained, leading to <inline-formula><tex-math id="M3">\begin{document}$ - {\gamma _2} \to {\gamma _1} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M3.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M3.png"/></alternatives></inline-formula>. After experiencing two resonance exchange processes, the final result is <inline-formula><tex-math id="M4">\begin{document}$ {\gamma _1} \to {\gamma _2} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M4.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M4.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M5">\begin{document}$ {\gamma _2} \to - {\gamma _1} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M5.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20240739_M5.png"/></alternatives></inline-formula>, which implies the realization of non-Abelian braiding operations. Our conclusion is that the modulation of coupling strength between two quantum dots can be used to achieve the switch of Majorana fermions braiding-like operation, which is independent of superconducting phase. Therefore, the designed scheme provides a new way for adjusting the braiding-like operation of Majorana fermions. These findings may have potential applications in the realization of topological quantum computers.

Quantum dense coding and teleportation based on two coupled quantum dot molecules influenced by intrinsic decoherence, tunneling rates, and Coulomb coupling interaction

Quantum dense coding and teleportation based on two coupled quantum dot molecules influenced by intrinsic decoherence, tunneling rates, and Coulomb coupling interaction

Prospecting Quantum Correlations and Examining Teleportation Fidelity in a Pair of Coupled Double Quantum Dots System

AbstractThe topic of improving the ability of quantum systems to retain non‐local features and enhance the efficiency of quantum protocols continues. This study delves into the thermal investigation of quantum correlations and teleportation fidelity of a two‐qubit teleported state using excess electrons in a coupled double quantum dots system as a quantum channel. The study employs three reliable quantum quantifiers to prospect the resourcefulness and non‐classicality of the system. The findings suggest that preserving quantum correlations and optimizing teleportation fidelity require minimizing tunneling coupling and maximizing Coulomb interaction. The study has significant implications for quantum physics and its practical applications in quantum information processing.

Abstract C136: Magnetic nanoparticles and quantum dots coupled visual confirmation of cervical cancer cells from cytology samples: A cost-effective, quick and suitable test for rural Indian set-up

Abstract Introduction Screening and management of cervical cancer is a National health priority of developed and developing countries like India. Cervical cancer screening and diagnosis are currently done by cervical pap screening, colposcopy, and nucleic acid hybridization and amplification assays, which are time-consuming and require specialized facilities. These shortcomings pose severe restrictions on the feasibility of the techniques for a country like India.Aim and objectives Bearing this in mind, we aimed to develop a simple, cost-effective, and visual detection of cervical cancer, based on magnetic nanoparticles coupled quantum dots immuno-nano-fluorescence assay (MNCQDINFA).Materials and methods The detection system comprised of magnetic nanoparticles(MNP) and quantum dots (QD) conjugated specific polyclonal antibodies complex generated against recombinantly purified individual domains (domainN and domainC) of HPV-16 oncoprotein E7, which is deregulated and overexpressed to detectable limits by transformed cervical cancer cells only [1-3]. The assay procedure involves incubating processed cervical cytology samples with MNP-Ab (domainN) complex, magnet-induced pelleting, incubation with QD-Ab (domainC) complex, magnet-assisted washing, and final reconstitution in sample buffer and visualization under UV (Figure). Reconstituted sample in the presence of UV gives fluorescence as an indication of the presence of E7 protein thus cervical cancer cells. Results This method produces a visual fluorescence exclusively in the presence of transformed cervical cancer cells under UV light. Analytical assays showed that a minimum of 0.1µg of E7 protein could be detected specifically from a pool of cellular proteins. HPV 16-positive cervical cancer cell lysates showed concordant results. Both the diagnostic sensitivity and specificity of the assay were determined to be 100%. Conclusion The proposed invention is a simple, visual (naked eye), quick (4 hours), and cost-effective (INR 200-300) cervical cancer cells detection method necessary to identify the candidates at risk so that suitable and timely intervention can be provided.

Light-Driven Metabolic Pathways in Non-Photosynthetic Biohybrid Bacteria.

Biomanufacturing via microorganisms relies on carbon substrates for molecular feedstocks and a source of energy to carry out enzymatic reactions. This creates metabolic bottlenecks and lowers the efficiency for substrate conversion. Nanoparticle biohybridization with proteins and whole cell surfaces can bypass the need for redox cofactor regeneration for improved secondary metabolite production in a non-specific manner. Here we propose using nanobiohybrid organisms (Nanorgs), intracellular protein-nanoparticle hybrids formed through the spontaneous coupling of core-shell quantum dots (QDs) with histidine-tagged enzymes in non-photosynthetic bacteria, for light-mediated control of bacterial metabolism. This proved to eliminate metabolic constrictions and replace glucose with light as the source of energy in Escherichia coli, with an increase in growth by 1.7-fold in 75 % reduced nutrient media. Metabolomic tracking through carbon isotope labeling confirmed flux shunting through targeted pathways, with accumulation of metabolites downstream of respective targets. Finally, application of Nanorgs with the Ehrlich pathway improved isobutanol titers/yield by 3.9-fold in 75 % less sugar from E. coli strains with no genetic alterations. These results demonstrate the promise of Nanorgs for metabolic engineering and low-cost biomanufacturing.

Optically Addressing Exciton Spin and Pseudospin in Nanomaterials for Spintronics Applications.

Oriented exciton spins that can be generated and manipulated optically are of interest for a range of applications, including spintronics, quantum information science, and neuromorphic computing architectures. Although materials that host such excitons often lack practical coherence times for use on their own, strategic transduction of the magnetic information across interfaces can combine fast modulation with longer-term storage and readout. Several nanostructure systems have been put forward due to their interesting magneto-optical properties and their possible manipulation using circularly polarized light. These material systems are presented here, namely two-dimensional (2D) systems due to the unique spin-valley coupling properties and quantum dots for their exciton fine structure. 2D magnets are also discussed for their anisotropic spin behavior and extensive 2D magnetic states that are not yet fully understood but could pave the way for emergent techniques of magnetic control. This review also details the experimental and theoretical tools to measure and understand these systems along with a discussion on the progress of optical manipulation of spins and magnetic order transitions.

Electron–phonon interaction and electronic correlations in transport through electrostatically and tunnel coupled quantum dots

We investigate two equivalent capacitively and tunnel coupled quantum dots, each coupled to its own pair of leads. Local Holstein type electron–phonon coupling at the dots is assumed. To study many-body effects we use the finite-U mean-field slave boson approach. For vanishing interdot interaction, weak e–ph coupling and finite tunneling, molecular orbital spin Kondo effects occur for single electron or single hole occupations. Phonons influence both correlations and tunneling and additionally they shift the energies of the dots. Depending on the dot energies and the strength of electron–phonon coupling, the system is occupied by a different number of electrons that effectively interact with each other repulsively or attractively leading to a number of different ground states of DQD. Among them are Kondo-like states with spin, orbital or charge correlations resulting from polaron cotunneling processes and states with magnetic intersite correlations.

Nonlinear optical properties of coupled quantum dots in peanut configuration

ABSTRACT This paper presents a theoretical investigation of nonlinear properties of coupled quantum dots in the peanut configuration. A complete Hamiltonian is formulated using the adiabatic method and the confinement energy is represented in a cylindrical coordinate system. The effective energy for the slow subsystem is analysed and graphed as a function of a fixed value of axial coordinate for both the asymmetric and symmetric peanut QD cases. The electron motion in the presence of an electric field in the vertical direction is considered, and the eigenfunctions and energy spectrum of electron motion are determined for the same direction utilising the finite element method. The dependence of the first three energy levels on the electric field is shown, and the electron probability density for the ground state and the first excited state is plotted. In addition, calculations for the nonlinear optical properties are presented, particularly optical rectification, second harmonic generation and third harmonic generation. The results demonstrate that these properties can be effectively controlled by varying the external electric field. The findings suggest that coupled peanut QDs hold significant potential for applications in high-performance optoelectronic devices.

Construction of Dual S‐Scheme Heterojunction Based Co9S8 QDs Coupling with NiS/CdS Concave Cubic Derived from Prussian Blue Analog for Enhanced Photocatalytic Hydrogen Evolution

AbstractThe design and development of high‐efficiency and low‐energy consumption catalysts for hydrogen evolution are critical to mitigating environmental problems. Herein, amorphous Co9S8 quantum dots (QDs) are prepared by hydrothermal method and loaded on concave cubic NiS/CdS derived from Prussian blue analog (PBA) to construct an efficient Co9S8 QDs/NiS/CdS dual S‐scheme heterojunction photocatalysts, showing excellent photocatalytic hydrogen performance of 13.45 mmol·g−1·h−1, which is 5.42 times higher than that of pure CdS. The improved photocatalytic performance is ascribed to the creation of a double S‐scheme heterojunction, quantum confinement effect, and a concave cubic structure, accelerating electron transport and offering ample surface active sites. The possible mechanism is demonstrated with valence band XPS (VB‐XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) calculations. This work provides insight into the exploration of PBA‐based photocatalysts to improve photocatalytic hydrogen evolution and provides an effective strategy for the design of photocatalysts with double the S‐scheme heterojunction.

Inverse current induced thermoelectric conversion in a parallel-coupled double quantum dot system

We investigate the thermoelectric transport and conversion of a parallel-coupled double quantum dot system, which consisting of two capacitively coupled quantum dots in the Coulomb-blockade regime. We found that the system exhibits an unconventional thermoelectric conversion process induced by the inverse current effect, which is attributed to the increased Coulombic interaction between quantum dots, resulting in strong asymmetry in the system. We study the transport properties of steady-state particle current and heat current, and analyze the influence of Coulomb interaction on the thermodynamic characteristics of unconventional thermoelectric heat engines and refrigerators.

Cooling by Coulomb Heat Drag Based on Three Coupled Quantum Dots

We establish a model for a four-terminal thermoelectric system, based on three coupled quantum dots, which consists of a left/right electron reservoir (the source and the drain), two thermal reservoirs and three coupled quantum dots. Based on the master equation theory, we derive the expressions of the electron current and heat flow among the three quantum dots and the corresponding reservoir. We show that the source can be cooled by passing a thermal current between the two thermal reservoirs, with no net heat exchange between the thermal reservoirs and the electron reservoirs. This effect is called the Coulomb heat drag effect. Then, we define the coefficient of performance (COP) and the cooling power. The influence of the main system parameters, such as charging energy, energy level, and temperature, on the performance of the four-terminal thermoelectric system is analyzed in detail. By choosing appropriate parameters one can obtain the maximum cooling power and the corresponding COP. Finally, we also show that the Maxwell demon effect can be realized by using nonequilibrium thermal reservoirs in our four-terminal thermoelectric system.

Fusion protocol for Majorana modes in coupled quantum dots

Fusion protocol for Majorana modes in coupled quantum dots

Coulomb staircase in an asymmetrically coupled quantum dot

We investigate the Coulomb blockade in quantum dots asymmetrically coupled to the leads for an arbitrary voltage bias focusing on the regime where electrons do not thermalise during their dwell time in the dot. By solving the quantum kinetic equation, we show that the current–voltage characteristics are crucially dependent on the ratio of the Fermi energy to charging energy on the dot. In the standard regime when the Fermi energy is large, there is a Coulomb staircase which is practically the same as in the thermalised regime. In the opposite case of the large charging energy, we identify a new regime in which only one step is left in the staircase, and we anticipate experimental confirmation of this finding.

Laser‐Printed Plasmonic Metasurface Supporting Bound States in the Continuum Enhances and Shapes Infrared Spontaneous Emission of Coupled HgTe Quantum Dots

AbstractIn order to advance the development of quantum emitter‐based devices, it is essential to enhance light‐matter interactions through coupling between semiconductor quantum dots with high quality factor resonators. Here, efficient tuning of the emission properties of HgTe quantum dots in the infrared spectral region is demonstrated by coupling them to a plasmonic metasurface that supports bound states in the continuum. The plasmonic metasurface, composed of an array of gold nanobumps, is fabricated using single‐step direct laser printing, opening up new opportunities for creating exclusive 3D plasmonic nanostructures and advanced photonic devices in the infrared region. A 12‐fold enhancement of the photoluminescence in the 900–1700 nm range is observed under optimal coupling conditions. By tuning the geometry of the plasmonic arrays, controllable shaping of the emission spectra is achieved, selectively enhancing specific wavelength ranges across the emission spectrum. The observed enhancement and shaping of the emission are attributed to the Purcell effect, as corroborated by systematic measurements of radiative lifetimes and optical simulations based on the numerical solution of Maxwell's equations. Moreover, coupling of the HgTe photoluminescence to high quality factor modes of the metasurface improves emission directivity, concentrating output within an ≈20° angle.