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Copper indium selenide (CISe) is a prototype infrared semiconductor with low toxicity and unique optical characteristics. Its quantum dots (QDs) accommodate ample intrinsic point defects which may actively participate in their rather complex photophysical processes. We synthesize CISe QDs with similar sizes but with distinct highly stoichiometry-deviating atomic ratios. The synthesis condition employing Se-rich precursors yields the Cu-deficient CISe QDs with special photophysical properties. The photoluminescence exhibits monotonic red shift from 680 to 775 nm when the ratio of Cu's proportion to In's decreases. The luminescence is found to stem from the copper vacancy and antisite defects. The CISe QDs exhibit Raman activity at 5.6, 6.9, and 8.7 THz that is separately assigned to Cu–Se and In–Se optical phonon modes and surface mode. [ABSTRACT FROM AUTHOR]

The rapid and accurate detection of pathogens is crucial for effective disease prevention and management in healthcare, food safety, and environmental monitoring. While conventional pathogen detection methods like culture-based techniques and PCR are sensitive and selective, they are often time-consuming, require skilled operators, and are not suitable for point-of-care or on-site testing. To address these limitations, innovative sensor technologies have emerged that leverage the unique properties of nanomaterials. Quantum dots (QDs) and magnetic nanomaterials are two classes of nanomaterials that have shown particular promise for pathogen sensing. This review comprehensively examines the synergistic applications of QDs and magnetic nanomaterials for detecting bacteria, viruses, phages, and parasites. [ABSTRACT FROM AUTHOR]

Zero-dimensional transition metal dichalcogenides (TMD) quantum dots (QDs) have attracted a lot of attention due to their interesting fundamental properties and various applications. Compared to TMD monolayers, the QD counterpart exhibits larger values for direct transition energies, exciton binding energies, absorption coefficient, luminescence efficiency, and specific surface area. These characteristics make them useful in optoelectronic devices. In this review, recent exciting progress on synthesis, optical properties, and applications of TMD QDs is highlighted. The first part of this article begins with a brief description of the synthesis approaches, which focus on microwave-assistant heating and pulsed laser ablation methods. The second part introduces the fundamental optical properties of TMD QDs, including quantum confinement in optical absorption, excitation-wavelength-dependent photoluminescence, and many-body effects. These properties are highlighted. In the third part, we discuss lastest advancements in optoelectronic devices based on TMD QDs These devices include light-emitting diodes, solar cells, photodetectors, optical sensors, and light-controlled memory devices. Finally, a brief summary and outlook will be provided. [ABSTRACT FROM AUTHOR]

Optical absorption spectra of GaSb/GaAs quantum-ring-with-dot structures (QRDSs) are calculated using Fermi's golden rule by which the electronic states involved in the optical transitions are obtained from the eight-band k ⋅ p method. The absorption spectra of multi-stacked QRDS layers show that the interband and intraband transitions are favorable to intermediate band solar cells (IBSCs). A drift-diffusion model with rate equations for a solar cell containing multi-stacked QRDS layers is formulated based on the absorption spectra. The external quantum efficiency (EQE) determined by the model with the AM1.5 solar spectrum and additional infrared light demonstrates that the confined hole states in the quantum ring (QR) parts of the QRDSs effectively function as an IB. The more efficient two-step photon absorption indicated by the enhancement of the EQE also suggests the potential of QRDSs for the IBSCs. [ABSTRACT FROM AUTHOR]

In this paper, we have examined the effectiveness exchange of optical vorticity via three-wave mixing (TWM) technique in a four-level quantum dot (QD) molecule by means of the electron tunneling effect. Our analytical analysis demonstrates that the TWM procedure can result in the production of a new weak signal beam that may be absorbed or amplified within the QD molecule. We have taken into account the electron tunneling as well as the relative phase of the applied lights to assess the absorption and dispersion characteristics of the newly generated light. We have discovered that the slow light propagation and signal amplification can be achieved. Our results show that the exchange of the orbital angular momentum of light can transfer from coupling optical vortex light to the new generated light in high efficiency. [ABSTRACT FROM AUTHOR]

How to control the charge and spin in nanodevices is an important topic in spintronics. In this letter, we theoretically propose a spin diode and spin valve (SV) device controlled by all-electrical means, which is composed of a quantum dot (QD) coupled to a pair of nonmagnetic electrodes. When both electric charge bias and spin bias exist within the device, the I – V curves of this device exhibit an asymmetric distribution, and this asymmetry can be manipulated by the gate voltage. More interestingly, if we apply an external magnetic field on the QD, we can observe significant high- and low-resistance state switching with respect to the magnetic field, which can function as a SV device. This device scheme can be compatible with current technologies and has potential applications in spintronics or quantum processing. [ABSTRACT FROM AUTHOR]

Time-resolved super-resolution microscopy was used in conjunction with scanning electron microscopy to image individual colloidal CdSe/CdS semiconductor quantum dots (QD) and QD dimers. The photoluminescence (PL) lifetimes, intensities, and structural parameters were acquired with nanometer scale spatial resolution and sub-nanosecond time resolution. The combination of these two techniques was more powerful than either alone, enabling us to resolve the PL properties of individual QDs within QD dimers as they blinked on and off, measure interparticle distances, and identify QDs that may be participating in energy transfer. The localization precision of our optical imaging technique was ∼3 nm, low enough that the emission from individual QDs within the dimers could be spatially resolved. While the majority of QDs within dimers acted as independent emitters, at least one pair of QDs in our study exhibited lifetime and intensity behaviors consistent with resonance energy transfer from a shorter lifetime and lower intensity donor QD to a longer lifetime and higher intensity acceptor QD. For this case, we demonstrate how the combined super-resolution optical imaging and scanning electron microscopy data can be used to characterize the energy transfer rate. [ABSTRACT FROM AUTHOR]

Quantum dots (QD) are rapidly making their way into several application sectors including optoelectronics, and there is a strong need to focus on non-toxic QDs. In this work, we have synthesized graphene QDs in the size range of 1.4–4.2 nm from inexpensive graphite by oxidative cleavage using a sulphuric and nitric acid mixture. A subsequent hydrogen peroxide oxidation step, investigated using two thermal budgets, has resulted in QDs with excellent photoluminescence (PL) intensity. Prolonged, higher temperature oxidation results in smaller size GQDs. X-ray photoelectron spectroscopy analysis confirmed the role of ·OH radicals in the oxidation process and Raman analysis revealed that the higher thermal budget oxidation results in lower defect density. To overcome the challenges in device adaptability due to the inherent acidity in the QDs, a post-synthesis neutralization process was devised. The neutralized GQDs were formed into a film to be used as the active layer in a photodetector device. Fluorescence decay analysis showed there is no significant change in lifetime because of the film formation process. The fabricated GQD photodetector device exhibited high photocurrent under ultraviolet illumination with an ON/OFF ratio of 400% at an applied bias of ±1 V. The device performance underlines the high potential for the non-toxic, top-down synthesized GQDs for application in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Single-photon emitters play a crucial role in integrated photonic quantum systems across various material platforms. In this study, we present a cavity-enhanced quantum dot single-photon source in a high-index contrast material platform (GaAs-on-insulator). A quantum dot is embedded in a microring resonator with a quality factor of approximately 9000, where the cavity-induced light enhancement results in a spontaneous emission acceleration factor of around 2.6, and we achieve a $g^{(2)}(0)$ as low as 0.03 ± 0.02 and post-selected two-photon interference visibility of 51.7 $\%\pm3.2\%$ for the single-photon source. This demonstration shows the potential of the GaAs-on-Insulator platform for scalable on-chip quantum information processing.

This study presents a machine learning-based procedure to automate the charge tuning of semiconductor spin qubits with minimal human intervention, addressing one of the significant challenges in scaling up quantum dot technologies. This method exploits artificial neural networks to identify noisy transition lines in stability diagrams, guiding a robust exploration strategy leveraging neural network uncertainty estimations. Tested across three distinct offline experimental datasets representing different single-quantum-dot technologies, this approach achieves a tuning success rate of over 99% in optimal cases, where more than 10% of the success is directly attributable to uncertainty exploitation. The challenging constraints of small training sets containing high diagram-to-diagram variability allowed us to evaluate the capabilities and limits of the proposed procedure.

Quantum dots have the potential to be one of the brightest deterministic single photon sources with high end applications in quantum computing and cluster state generation. In this work, we re-examine the design of plain micropillars by meticulously examining the structural effects of the decay into leaky channels beyond an atom-like cavity estimation. We show that precise control of the side losses with the diameter and avoidance of propagating Bloch modes in the distributed Bragg reflectors can result in easy-to-manufacture broadband ( $\mathit{Q}\approx750$ –2500) micropillars, allowing for broad optical coherent control pulses necessary for high single photon purity ( $ {\gt}$ 99.2%–99.99% achievable) while simultaneously demonstrating extremely high efficiency out the top (90.5%–96.4%). We also demonstrate that such cavities naturally decouple from the phonon sideband, with the phonon sideband reducing by a factor of 5–33 allowing us to predict that the photons should show 98.5%–99.8% indistinguishability without the need for filtering.

The Nobel Prizes in Physics (2022) and Chemistry (2023) heralded the recognition of quantum information science and the synthesis of quantum dots (QDs), respectively. This acknowledgment has propelled colloidal QDs and perovskite nanocrystals to the forefront of quantum technologies. Their distinct emission properties, facilitating the efficient generation of both single photons and photon pairs, render them particularly captivating. Moreover, their adaptability to diverse structures, ranging from traditional electronics to nanopatterned frameworks, underscores their pivotal role in shaping quantum technologies. Despite notable strides in synthesis, certain properties require refinement for enhanced applicability in quantum information, encompassing emission brightness, stability, single-photon indistinguishability, and entanglement fidelity of photon pairs. Here we offer an overview of recent achievements in plasmon-exciton quantum emitters (QEs) based on luminescent semiconductor nanocrystals. Emphasizing the utilization of the light-matter coupling phenomenon, we explore how this interaction enables the manipulation of quantum properties without altering the chemical structure of the emitters. This approach addresses critical aspects for quantum information applications, offering precise control over emission rate, intensity, and energy. The development of these hybrid systems represents a significant stride forward, demonstrating their potential to overcome existing challenges and advance the integration of QEs into cutting-edge quantum technology applications.

This study investigates nanobeam cavities on a GaAs-on-insulator (GaAsOI) chip with InAs quantum dots (QDs), including design, fabrication, and experimental characterization. The nanobeam cavities are optimized for high photon coupling efficiency and pronounced light-matter interaction. Numerical studies yield Q factors up to about 1400, a coupling efficiency of nearly 70 $\%$ and a maximum Purcell factor of approximately 100. Experimentally, these devices have a Q factor of about 1300, and comparing the lifetime of QDs in on-resonance and off-resonance conditions, a Purcell factor of $10.46\pm0.14$ is obtained. Moreover, in the single-emitter regime, we observe strong multiphoton suppression with $g^{(2)}(0) = 0.297$ . Our results demonstrate the high potential of nanobeam cavities on a GaAsOI platform for quantum photonic applications.

One of the most important feature in the Kondo physics is the universal scaling behavior. In this study, we analyze the transport behavior of the spin thermocurrent driven by a small temperature bias and under a weak magnetic field. We conclude that the spin thermocurrent exhibits a universal scaling behavior, similar to the spin susceptibility. The validity of our conclusion is also checked by using the numerically exact hierarchical equations of motion approach. From our fitting result of the scaling function, it is found that the Kondo temperature can be determined by the maximum of the spin thermocurrent at $T/T_K = 0.383$ .

We explore the dynamical behaviors of the measurement uncertainty and quantum correlation for a vertical quantum-dot system in the presence of magnetic field, including electron-electron interaction and Coulomb-blocked systems. Stemming from the quantum-memory-assisted entropic uncertainty relation, the uncertainty of interest is associated with temperature and parameters related to the magnetic field. Interestingly, the temperature has two kinds of influences on the variation of measurement uncertainty with respect to the magnetic-field-related parameters. We also discuss the relation between the lower bound of Berta et al. and the quantum discord. It is found that there is a natural competition between the quantum discord and the entropy min Πi B S Πi B (ρ A | B ) . Finally, we bring in two improved bounds to offer a more precise limit to the entropic uncertainty. [ABSTRACT FROM AUTHOR]

We theoretically investigate the four wave mixing (FWM) and normal mode splitting (NMS) in coupled double quantum dots cavity system in the presence of a third-order Kerr nonlinear χ (3) medium. The FWM generated in the system has narrow spectral width and this can be tuned by nonlinear medium strength, the coupling strength between two coupled quantum dots and pump strength. Further, we study NMS that can also be tuned by various physical parameters and show that energy exchange between different modes is possible. The proposed model have potential applications in the field of quantum information processing. [ABSTRACT FROM AUTHOR]

InN/InGaN quantum dots (QDs) are found to establish a nonlinear constant phase element (CPE) response over a wide frequency range, measured by electrochemical impedance spectroscopy (EIS). The intrinsic surface donors together with the near-surface electron accumulation layer form the fractional capacitor. The magnitude of the impedance and the phase angle depend on the QD structural parameters and contact area. Importantly, they consistently change with applied voltage, constituting the nonlinear CPE response. A noise-filtering DC voltmeter with the phase angle as readout is proposed. [ABSTRACT FROM AUTHOR]

We fabricated inorganic–organic hybrid quantum-dot light-emitting-diodes (QD-LEDs) consisting of several types of solution-processed n-type oxide electron injection layers (EILs)/quantum-dot (QD) and poly (9-vinylcarbazole) (PVK) blend light emitting layer (EMLs)/4,4-bis(carbazole-9yl)bihpheyl (CBP)/a-NPD/1,4,5,8,9, 11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) hole injection layer/Al structures. We compared the electrical properties of hybrid QD-LEDs with solution-processed n-type oxide electron injection layers consisting of Al-doped ZnO nano-particles (AZO-NP), polyethyleneimine (PEI), titanium oxide nanosheet (TiO-NS) on PEI (PEI/TiO-NS), and AZO-NP/TiO-NS multilayers. The combination of the PEI dipole layer and ultra-thin TiO-NS nanosheet (∼1 nm) layers reduced the potential barrier at ITO/TiO-NS interface. However, a considerable barrier height of >0.3 eV exists at the TiO-NS/QD interface. The use of small-work function AZO-NP (3.9 eV) effectively improves external quantum efficiency (EQE) compared with relatively large work-function AZO-NP (4.3 eV) and TiO-NS (4.1 eV). The capacitance–voltage curves and the current density–voltage–luminance curves strongly depend on the thickness of the QD:PVK blend (2:1 in weight) layer, and we obtained the optimized thickness for EML as ca. 30 nm. With the improved charge balance and morphology, an EQE of above 3.0% is obtained for green light-emitting QD-LED and an EQE of 0.86% for blue light-emitting QD-LED. [ABSTRACT FROM AUTHOR]

We theoretically propose an all-electrically controlled spin-current diode consisting of a quantum dot sandwiched between one normal electrode and one ferromagnetic electrode. By applying a spin bias V S across one electrode, the spin current distribution shows a rectification effect; that is, in the forward spin bias regime, a spin current can tunnel through the junction, while in the reverse bias regime, the current is tiny. Such asymmetry in the spin-current profile suggests diode-like behaviour with respect to the spin bias. Moreover, the polarity direction of this spin-current diode can be manipulated and reversed by adjusting the gate voltage, which is much more feasible than the approach with traditional charge-current diodes. The present device can be realized by current technologies and has potential applications in spintronics or quantum information processing. [ABSTRACT FROM AUTHOR]

Random signal generation in a ring resonator laser is achieved with quantum-dot semiconductor optical amplifiers. The lasing spectra were obtained over a wide range of wavelengths, and the individual longitudinal modes acted as the channels for random number generation. [ABSTRACT FROM AUTHOR]

We experimentally studied the influence of both impurity density and dangling-bond density on PL emissions from group-IV-semiconductor quantum-dots (IV-QDs) of Si and SiC fabricated by hot-ion implantation technique, to improve the PL intensity (I PL) from IV-QDs embedded in two types of insulators of quartz-glass (QZ) with low impurity density and thermal-oxide (OX) layers. First, we verified the I PL reduction in the IV-QDs in QZ. However, we demonstrated the I PL enhancement of IV-QDs in doped QZ, which is attributable to multiple-level emission owing to acceptor and donor ion implantations into QZ. Secondly, we confirmed the large I PL enhancement of IV-QDs in QZ and OX, owing to forming-gas annealing with H2/N2 mixed gas, which are attributable to the reduction of the dangling-bond density in IV-QDs. Consequently, it is possible to improve the I PL of IV-QDs by increasing impurity density and reducing dangling-bond density. [ABSTRACT FROM AUTHOR]

Two kinds of raw material combinations for the hot injection method were investigated for the chemical synthesis of SnSSe nanosheets and nanocrystals, which are low-toxic optoelectronic materials. When SnSe quantum dots were synthesized by mainly using oleic acid as the Se precursor solvent, the quantum dots changed from spherical to cubic as the size increased. The growth condition dependence of the nanocrystal formation process was discussed. When SnSSe nanocrystals were synthesized by mainly using trioctylphosphine as the S Se precursor solvent, it was found that the nanocrystal shape changed from dot to rod or sheet by reducing the proportion of S. The bandgap energy did not simply depend on the composition ratio of S but was affected by the change in the nanocrystal shape depending on the quantum confinement effect. [ABSTRACT FROM AUTHOR]

New characteristics of the Kondo effect, arising from spin chirality induced by the Berry phase in the equilibrium state, are investigated. The analysis is based on the hierarchical equations of motion (HEOM) approach in a triangular triple quantum-dot (TTQD) structure. In the absence of magnetic field, TTQD has four-fold degenerate chiral ground states with degenerate spin chirality. When a perpendicular magnetic field is applied, the chiral interaction is induced by the magnetic flux threading through TTQD and the four-fold degenerate states split into two chiral state pairs. The chiral excited states manifest as chiral splitting of the Kondo peak in the spectral function. The theoretical analysis is confirmed by the numerical computations. Furthermore, under a Zeeman magnetic field B, the chiral Kondo peak splits into four peaks, owing to the splitting of spin freedom. The influence of spin chirality on the Kondo effect signifies an important role of the phase factor. This work provides insight into the quantum transport of strongly correlated electronic systems. [ABSTRACT FROM AUTHOR]

In this paper, we analyze superstructural transitions during epitaxial growth of two-dimensional layers and the formation of quantum dots by the Stranskiâ€"Krastanov mechanism in elastically stressed systems by the reflection high-energy electron diffraction method. Detailed dependences of the periodicity parameter N of the 2 × N reconstruction on the effective thickness of the deposited material in a wide range of growth temperatures during epitaxy of germanium on a silicon surface with a crystallographic orientation (001) are obtained. Superstructural transitions and the change in the value of the parameter N at low temperatures of epitaxy in this system have been investigated for the first time. It is shown that the length of dimer rows in such a reconstruction during the growth of pure germanium on silicon can reach a value of no less than N  = 11. A relationship is found between the value of the parameter N, determined by elastic strains in the system, and the critical thickness of the transition from two-dimensional to three-dimensional growth. Based on this relationship, a physical mechanism is proposed that explains the nature of the temperature dependence of the critical thickness of the Stranskiâ€"Krastanov transition, which has been the subject of constant scientific disputes until now. [ABSTRACT FROM AUTHOR]

The electrical control of a spin qubit in a quantum dot (QD) relies on spinâ€"orbit coupling (SOC), which could be either intrinsic to the underlying crystal lattice or heterostructure, or extrinsic via, for example, a micro-magnet. In experiments, micromagnets have been used as a synthetic SOC to enable strong coupling of a spin qubit in quantum dots with electric fields. Here we study theoretically the spin relaxation, pure dephasing, spin manipulation, and spinâ€"photon coupling of an electron in a QD due to the synthetic SOC induced spinâ€"orbit mixing. We find qualitative difference in the spin dynamics in the presence of a synthetic SOC compared with the case of the intrinsic SOC. Specifically, spin relaxation due to the synthetic SOC and deformation potential phonon emission (or Johnson noise) shows B 0 5 (or B 0) dependence with the magnetic field, which is in contrast with the B 0 7 (or B 0 3 ) dependence in the case of the intrinsic SOC. Moreover, charge noise induces fast spin dephasing to the first order of the synthetic SOC, which is in sharp contrast with the negligible spin pure dephasing in the case of the intrinsic SOC. These qualitative differences are attributed to the broken time-reversal symmetry (T -symmetry) of the synthetic SOC. An SOC with broken T -symmetry (such as the synthetic SOC from a micro-magnet) eliminates the ‘Van Vleck cancellation’ and causes a finite longitudinal spinâ€"electric coupling that allows the longitudinal coupling between spin and electric field, and in turn allows spin pure dephasing. Finally, through proper choice of magnetic field orientation, the electric-dipole spin resonance via the synthetic SOC can be improved with potential applications in spin-based quantum computing. [ABSTRACT FROM AUTHOR]

Electron spins in gate-defined lateral quantum dots (QDs) are a suitable platform for qubits and have the capacity for coherent coupling to free-space photons. Superposition state transfer from single photon polarizations to single spins has been realized using a GaAs gate-defined QD. However, its efficiency is limited by the small size of the QDs. Here, we use a surface plasmon antenna on a GaAs gate-defined QD and demonstrate that the photoelectron detection probability is enhanced by 5.3â€"9.2 times. This result contributes to the development of photonâ€"spin quantum interface using gate-defined lateral QDs. [ABSTRACT FROM AUTHOR]

We study (In,Ga)(As,Sb)/GaAs quantum dots (QDs) embedded in a GaP (100) matrix, which are overgrown by a thin GaSb capping layer with variable thickness. QD samples are studied by temperature-dependent photoluminescence, and we observe that the QD emission shows anomalous temperature dependence, i.e. increase of energy with temperature increase from 10 K to ∼70 K, followed by energy decrease for larger temperatures. With the help of fitting of luminescence spectra by Gaussian bands with energies extracted from eight band $\textbf{k}\cdot\textbf{p}$ theory with multiparticle corrections calculated using the configuration interaction method, we explain the anomalous temperature dependence as mixing of momentum direct and indirect exciton states. We also find that the k -indirect electron–hole transition in type-I regime at temperatures ${\lt} 70$ K is optically more intense than k -direct. Furthermore, we identify a band alignment change from type-I to type-II for QDs overgrown by more than one monolayer of GaSb. Finally, we predict the retention time of (In,Ga)(As,Sb)/GaAs/AlP/GaP QDs capped with GaSb layers with varying thickness, for usage as storage units in the QD-Flash nanomemory concept and observe that by using only a 2 ML-thick GaSb capping layer, the projected storage time surpasses the non-volatility limit of ten years.

A major challenge in generating single photons with a single emitter is to excite the emitter while avoiding laser leakage into the collection path. Ideally, any scheme to suppress this leakage should not result in a loss in the efficiency of the single-photon source. Here, we investigate a scheme in which a single emitter, a semiconductor quantum dot, is embedded in a microcavity. The scheme exploits the splitting of the cavity mode into two orthogonally-polarised modes: one mode is used for excitation, the other for collection. By linking the experiment to theory, we show that the best population inversion is achieved with a laser pulse detuned from the quantum emitter. The Rabi oscillations exhibit an unusual dependence on pulse power. Our theory describes them quantitatively, enabling us to determine the absolute population inversion. By comparing the experimental results with our theoretical model, we determine a population inversion of $98\%^{+1\%}_{-5\%}$ for optimal laser detuning. The Rabi oscillations depend on the sign of the laser-pulse detuning, a phenomenon arising from the non-trivial effect of phonons on the exciton dynamics. The exciton–phonon interaction is included in the theory and gives excellent agreement with all the experimental results.

The performance and scalability of silicon spin qubits depend directly on the value of the conduction band valley splitting (VS). In this work, we investigate the influence of electromagnetic fields and the interface width on the VS of a quantum dot in a Si/SiGe heterostructure. We propose a new three-dimensional theoretical model within the effective mass theory for the calculation of the VS in such heterostructures that takes into account the concentration fluctuation at the interfaces and the lateral confinement. With this model, we predict that the electric field is an important parameter for VS engineering, since it can shift the probability distribution away from small VSs for some interface widths. We also obtain a critical softness of the interfaces in the heterostructure, above which the best option for spin qubits is to consider an interface as wide as possible.

We study the property of magnetopolaron in a parabolic quantum dot under the Rashba spinâ€"orbit interaction (RSOI) by adopting an unitary transformation of Leeâ€"Lowâ€"Pines type and the variational method of Pekar type with and without considering the temperature. The temporal spatial distribution of the probability density and the relationships of the oscillating period with the RSOI constant, confinement constant, electronâ€"phonon coupling strength, phonon wave vector and temperature are discussed. The results show that the probability density of the magnetopolaron in the superposition of the ground and first excited state takes periodic oscillation (T 0/period) in the presence or absence of temperature. Because of the RSOI, the oscillating period is divided into different branches. Also, the results indicate that the oscillating period increases (decreases) when the RSOI constant, electron-phonon coupling strength and phonon wave vector (the confinement constant) increase in a proper temperature, and the temperature plays a significant role in determining the properties of the polaron. [ABSTRACT FROM AUTHOR]

The spin transport properties are theoretically investigated when a quantum dot (QD) is side-coupled to Majorana bound states (MBSs) driven by a symmetric dipolar spin battery. It is found that MBSs have a great effect on spin transport properties. The peak-to-valley ratio of the spin current decreases as the coupling strength between the MBS and the QD increases. Moreover, a non-zero charge current with two resonance peaks appears in the system. In the extreme case where the dotâ€"MBS coupling strength is strong enough, the spin current and the charge current are both constants in the non-resonance peak range. When considering the effect of the Zeeman energy, it is interesting that the resonance peak at the higher energy appears one shoulder. And the shoulder turns into a peak when the Zeeman energy is big enough. In addition, the coupling strength between the two MBSs weakens their effects on the currents of the system. These results are helpful for understanding the MBSs signature in the transport spectra. [ABSTRACT FROM AUTHOR]

Terahertz (THz) vector beams with spatially textured polarization are proposed to steer the spin and spatial distributions of two interacting electrons in a quantum dot. We study theoretically the spatiotemporal evolution of the spin and the charge-current densities and quantify the behavior of entanglement by calculating the concurrence. Both aspects are shown to be controllable efficiently and on the picosecond (ps) time scale by the parameters of the driving fields. Analyzing two different materials, GaAs and InGaAs, with different electron g -factors, we study the relationship between the g -factor and type of spin–orbit coupling required to produce efficient interlevel transitions. The results are useful for applications of quantum dots as basic nanoscale hardware elements in quantum information technology and for producing swiftly the appropriate spin and charge currents on demand.

Conversion of temperature gradients to charge currents in quantum dot systems enables probing various concepts from highly efficient energy harvesting and fundamental thermodynamics to spectroscopic possibilities complementary to conventional bias device characterization. In this work, we present a proof-of-concept study of a device architecture where bottom-gates are capacitively coupled to an InAs nanowire and double function as local joule heaters. The device design combines the ability to heat locally at different locations on the device with the electrostatic definition of various quantum dot and barrier configurations. We demonstrate the versatility of this combined gating- and heating approach by studying, as a function of the heater location and bias, the Seebeck effect across the barrier-free nanowire, fit thermocurrents through quantum dots for thermometry and detect the phonon energy using a serial double quantum dot. The results indicate symmetric heating effects when the device is heated with different gates and we present detection schemes for the electronic and phononic heat transfer contribution across the nanowire. Based on this proof-of-principle work, we propose a variety of future experiments.

The electrical control of a spin qubit in a quantum dot (QD) relies on spin–orbit coupling (SOC), which could be either intrinsic to the underlying crystal lattice or heterostructure, or extrinsic via, for example, a micro-magnet. In experiments, micromagnets have been used as a synthetic SOC to enable strong coupling of a spin qubit in quantum dots with electric fields. Here we study theoretically the spin relaxation, pure dephasing, spin manipulation, and spin–photon coupling of an electron in a QD due to the synthetic SOC induced spin–orbit mixing. We find qualitative difference in the spin dynamics in the presence of a synthetic SOC compared with the case of the intrinsic SOC. Specifically, spin relaxation due to the synthetic SOC and deformation potential phonon emission (or Johnson noise) shows ${B}_{0}^{5}$ (or B _0 ) dependence with the magnetic field, which is in contrast with the ${B}_{0}^{7}$ (or ${B}_{0}^{3}$ ) dependence in the case of the intrinsic SOC. Moreover, charge noise induces fast spin dephasing to the first order of the synthetic SOC, which is in sharp contrast with the negligible spin pure dephasing in the case of the intrinsic SOC. These qualitative differences are attributed to the broken time-reversal symmetry ( T -symmetry) of the synthetic SOC. An SOC with broken T -symmetry (such as the synthetic SOC from a micro-magnet) eliminates the ‘Van Vleck cancellation’ and causes a finite longitudinal spin–electric coupling that allows the longitudinal coupling between spin and electric field, and in turn allows spin pure dephasing. Finally, through proper choice of magnetic field orientation, the electric-dipole spin resonance via the synthetic SOC can be improved with potential applications in spin-based quantum computing.

We study the energy levels of graphene magnetic circular quantum dot surrounded by an infinite graphene sheet in the presence of an electrostatic potential. We solve Dirac equation to derive the solutions of energy spectrum associated with different regions composing our system. Using the continuum model and applying boundary conditions at the interface, we obtain analytical results for the energy levels. The dependence of the energy levels on the quantum dot radius, magnetic field and electrostatic potential is analyzed for the two valleys K and $K^{\prime} $ . We show that the energy levels exhibit characteristics of interface states and have an energy gap.

For their ultra-wide color gamut, high efficiency, robustness, and solution processability, Cd-based alloy semiconductor quantum dots (AQDs) continue to proliferate by driving innovations in the fields of optoelectronics, photovoltaics, multiplex bio-imaging, and cancer research. Herein, non-toxic, low-cost isopropyl alcohol vapor-based oxidative treatment protocol is developed and applied to tune the light emission spectrum of crystalline core–shell CdSe _1−x S _x /ZnS quantum dots. As evidenced by the results of structural investigations, these AQDs when exposed to vapors produced ultrasonically from 10:1 isopropyl alcohol-to-water mix undergo an isotropic, diameter non-specific size reduction at the rate of ∼1.3 Å min ^−1 . Nonlinear time-dependent spectral shifts, revealed experimentally, are consistent with the results of the effective-mass approximation treatment. The emission yields are seen to undergo an initial drop, yet to plateau as the etch time increases. The study opens a door to a soft, top-down monotonic tailoring of the light emission characteristics and opto-electronic response of stoichiometrically- and hierarchically-complex core–shell constructs in technologically-viable group II–VI nano-semiconductors as well as AQD-based catalytic conversion of organic compounds.

Si quantum dots (QDs) have a significant improvement in luminous efficiency compared with bulk Si, achieved by alleviating the forbiddance of no-phonon Γ – Γ radiative transition determined by the law of momentum conservation. Two divergent mechanisms have been proposed to account for the breakdown of momentum conservation in Si QDs, one is due to the space-confinement-induced spread of k -space wave functions associated with Heisenberg uncertainty principle Δ r · Δ k > 1/2, and the other is due to the interface-effect-induced intervalley mixing between indirect and direct bandgap states. Both mechanisms could cause a small overlap of the electron and hole wave functions in k -space and make vertical transitions allowed, which leads to the zero-phonon light emission. In this work, we unravel the hierarchical relationship between these two primary mechanisms in the process of zero-phonon light emission from indirect bandgap QDs, by performing semiempirical pseudopotential calculation including many-body interaction on the room-temperature luminescent properties of a series of Si, Ge, and Ge/Si core/shell QDs. We show that the space confinement mechanism is dominant in both Si and Ge indirect bandgap QDs, and the interface-induced intervalley coupling mechanism plays a minor role. While in Ge/Si core/shell QDs, the interface-induced intervalley coupling mechanism has a more pronounced contribution to enhanced light emission, implying one can further enhance light emission via engineering interface based on the intervalley coupling mechanism. Given this, we further engineer the Ge QD interface by bringing four motifs of Si/Ge multiple layers from previously inverse designed Si/Ge superlattices and core/shell nanowires for light emitters. We show that two out of four motifs always give rise to two orders of magnitude enhancement in light emission relative to the Ge and Si QDs. We demonstrate that the interface engineering can enhance light emission in indirect bandgap QDs substantially and regulate the intervalley coupling mechanism as the primary factor over the space confinement mechanism in breaking the momentum conservation law.

Universal quantum gates are the core elements in quantum information processing. We design two schemes to realize more general (SWAP) ^1/ ^m and controlled-(swap) ^1/ ^m gates (for integer $m\geqslant 1$ ) by directing flying single photons to solid-state quantum dots. The parameter m is easily controlled by adjusting two quarter-wave plates and one half-wave plate. Additional computational qubits are not required to construct the two gates. Evaluations of the gates indicate that our proposals are feasible with current experimental technology.

We combine electrostatic and magnetic confinement to define a quantum dot in bilayer graphene. The employed geometry couples n -doped reservoirs to a p -doped dot. At magnetic field values around $B=2$ T, Coulomb blockade is observed. This demonstrates that the coupling of the copropagating modes at the p – n interface is weak enough to form a tunnel barrier, facilitating transport of single charge carriers onto the dot. This result may be of use for quantum Hall interferometry experiments.

Many quantum dot qubits operate in regimes where the energy splittings between qubit states are large and phonons can be the dominant source of decoherence. The recently proposed charge quadrupole qubit, based on one electron in a triple quantum dot, employs a highly symmetric charge distribution to suppress the influence of long-wavelength charge noise. To study the effects of phonons on the charge quadrupole qubit, we consider Larmor and Ramsey pulse sequences to identify favorable operating parameters. We show that phonon-induced decoherence increases with the qubit frequency, in contrast to the effects of charge noise. We also show that there is an optimum value of the tunnel coupling of the qubit at which the decohering effects of phonons and charge noise are small enough to be consistent with single qubit gate fidelities > 99.99%.

We investigate the dynamics of charge-state coherence in a degenerate double-dot Aharonov–Bohm interferometer with finite inter-dot Coulomb interactions. The quantum coherence of the charge states is found to be sensitive to the transport setup configurations, involving both the single-electron impurity channels and the Coulomb-assisted ones. We numerically demonstrate the emergence of a complete coherence between the two charge states, with the relative phase being continuously controllable through the magnetic flux. Interestingly, a fully coherent charge qubit arises at the double-dots electron pair tunneling resonance condition, where the chemical potential of one electrode is tuned at the center between a single-electron impurity channel and the related Coulomb-assisted channel. This pure quantum state of charge qubit could be experimentally realized at the current–voltage characteristic turnover position, where differential conductance sign changes. We further elaborate the underlying mechanism for both the real-time and the stationary charge-states coherence in the double-dot systems of study.

We theoretically investigate the propagation of heat currents in a three-terminal quantum dot engine. Electron–electron interactions introduce state-dependent processes which can be resolved by energy-dependent tunneling rates. We identify the relevant transitions which define the operation of the system as a thermal transistor or a thermal diode. In the former case, thermal-induced charge fluctuations in the gate dot modify the thermal currents in the conductor with suppressed heat injection, resulting in huge amplification factors and the possible gating with arbitrarily low energy cost. In the latter case, enhanced correlations of the state-selective tunneling transitions redistribute heat flows giving high rectification coefficients and the unexpected cooling of one conductor terminal by heating the other one. We propose quantum dot arrays as a possible way to achieve the extreme tunneling asymmetries required for the different operations.