Quantum Dot Arrays Research Articles

Efficient characterization of a double quantum dot using the Hubbard model

Semiconductor quantum dots are favorable candidates for quantum information processing due to their long coherence time and potential scalability. However, the calibration and characterization of interconnected quantum dot arrays have proven to be challenging tasks. One method to characterize the configuration of such an array involves using the Hubbard model. In this paper, we present an efficient characterization algorithm that efficiently extracts the Hubbard model parameters, including tunnel coupling and capacitive coupling energy, from experimental stability diagrams. Leveraging the dual-annealing optimizer, we determine the set of Hubbard parameters that best characterize the experimental data. We compare our method with an alternate, well-established measure of tunnel coupling and find good agreement within the investigated regime. Our extracted tunnel couplings range from 69 to 517 μeV, and we discuss the limiting factors of our method.

Protecting coherence from the environment via Stark many-body localization in a Quantum-Dot Simulator

Semiconductor platforms are emerging as a promising architecture for storing and processing quantum information, e.g., in quantum dot spin qubits. However, charge noise coming from interactions between the electrons is a major limiting factor, along with the scalability of many qubits, for a quantum computer. We show that a magnetic field gradient can be implemented in a semiconductor quantum dot array to induce a local quantum coherent dynamical ℓ−bit exhibiting the potential to be used as logical qubits. These dynamical ℓ−bits are responsible for the model being many-body localized. We show that these dynamical ℓ−bits and the corresponding many-body localization are protected from all noises, including phonons, for sufficiently long times if electron-phonon interaction is not non-local. We further show the implementation of thermalization-based self-correcting logical gates. This thermalization-based error correction goes beyond the standard paradigm of decoherence-free and noiseless subsystems. Our work thus opens a new venue for passive quantum error correction in semiconductor-based quantum computers.

Deformation effect on graphene quantum dot/graphane and silicene quantum dot/silicane array

This article presents a design for the two-dimensional heterostructure systems (2DHS) consisting of graphene quantum dot (QD) array in graphane (GQD/Graphane) and silicene QD array in silicane (SiQD/Silicane). First-principles method was used to evaluate the effect of deformation on the magnetism and electronic properties of these 2DHS. For the band engineering, the tuning range of the energy gap of GQD/Graphane and SiQD/Silicane 2DHS can be up to 1.20 and 1.35 eV, respectively, through strains ranging from −7% to 10 %. A strain-sharing effect is found, wherein the hydrogenated region shares a portion of strain within the QD array. This effect is stronger in SiQD/silicane than in GQD/graphane. Strain sharing enhances band coupling between the QDs and their hydrogenated counterpart in the low-energy region. This alters the electronic properties of the 2DHS and the magnetic properties of triangular and parallelogram SiQD/Silicane arrays under large compressive strain. Strain modulates the band gap of 2DHS, triggers a phase transition from semiconductor to metal in SiQD/Silicane systems under homogeneous strain, and removes the magnetism of triangular and parallelogram SiQD arrays under compressive strain. These findings suggest that the 2DHS could be promising for designing nanoelectronic devices and binary logic based on nanoscale magnetism.

Magneto-optical properties of a quantum dot array interacting with a far-infrared photon mode of a cylindrical cavity

Magneto-optical properties of a quantum dot array interacting with a far-infrared photon mode of a cylindrical cavity

Recent advances of photolithography patterning of quantum dots for micro-display applications

The preparation of red, green, and blue quantum dot (QD) pixelated arrays with high precision, resolution, and brightness poses a significant challenge on the development of advanced micro-displays for virtual, augmented, and mixed reality applications. Alongside the controlled synthesis of high-performance QDs, a reliable QD patterning technology is crucial in overcoming this challenge. Among the various methods available, photolithography-based patterning technologies show great potentials in producing ultra-fine QD patterns at micron scale. This review article presents the recent advancements in the field of QD patterning using photolithography techniques and explores their applications in micro-display technology. Firstly, we discuss QD patterning through photolithography techniques employing photoresist (PR), which falls into two categories: PR-assisted photolithography and photolithography of QDPR. Subsequently, direct photolithography techniques based on photo-induced crosslinking of photosensitive groups and photo-induced ligand cleavage mechanisms are thoroughly reviewed. Meanwhile, we assess the performance of QD arrays fabricated using these photolithography techniques and their integration into QD light emitting diode display devices as well as color conversion-based micro light emitting diode display devices. Lastly, we summarize the most recent developments in this field and outline future prospects.

Magnetic Properties of A Cavity‐Embedded Square Lattice of Quantum Dots or Antidots

AbstractQuantum electrodynamical density functional theory is applied to obtain the electronic density, spin polarization, as well as orbital and spin magnetizations of square periodic arrays of quantum dots or antidots subjected to the influence of a far‐infrared cavity photon field. A gradient‐based exchange‐correlation functional adapted to a 2D electron gas in a transverse homogeneous magnetic field is used in the theoretical framework and calculations. The obtained results predict a non‐trivial effect of the cavity field on the electron distribution in the unit cell of the superlattice, as well as on the orbital and spin magnetizations. The number of electrons per unit cell of the superlattice is shown to play a crucial role in the modification of the magnetization via the electron–photon coupling. The calculations show that cavity photons strengthen the diamagnetic effect in the quantum dot structure, while they weaken the paramagnetic effect in the antidot structure. As the number of electrons per unit cell of the lattice increases, the electron–photon interaction reduces the exchange forces that will otherwise promote strong spin splitting for both the dot and the antidot arrays.

Majorana Qubits and Non-Abelian Physics in Quantum Dot–Based Minimal Kitaev Chains

The possibility of engineering artificial Kitaev chains in arrays of quantum dots coupled via narrow superconducting regions has emerged as an attractive way to overcome the disorder issues that complicate the realization and detection of topological superconducting phases in other platforms. Although a true topological phase would require long chains, a two-site chain realized in a double quantum dot can already be tuned to points in parameter space where it hosts zero-energy states that seem identical to the Majorana bound states that characterize a topological phase. These states have been named “poor man’s Majorana bound states” (PMMs) because they lack formal topological protection. In this work, we propose a pathway for next-generation experiments on PMMs. The pathway starts with experiments to characterize a single pair of PMMs by measuring the Majorana quality and then moves on to initialization and readout of the parity of a PMM pair, which allows the measurement of quasiparticle poisoning times. The next step is to couple two PMM systems to form a qubit. We discuss measurements of the coherence time of such a qubit, as well as a test of Majorana fusion rules in the same setup. Finally, we propose and analyze three different types of braidinglike experiments that require more complex device geometries. Our conclusions are supported by calculations based on a realistic model with interacting and spinful quantum dots, as well as by simpler models to gain physical insight. Our calculations show that it is indeed possible to demonstrate non-Abelian physics in minimal two-site Kitaev chains despite the lack of a true topological phase. However, our findings also reveal that doing so requires some extra care, appropriately modified protocols, and awareness of the details of this particular platform. Published by the American Physical Society 2024

High‐Resolution Full‐Color Quantum Dots Patterning for Display Applications Based on Femtosecond Laser‐induced Forward Transfer

AbstractColloidal quantum dots (QDs) have been widely studied in display panels due to their near‐unity fluorescence quantum yield and the ability to tune colors across a wide gamut. However, the challenge persists in creating full‐color QD arrays with the necessary precision for high‐resolution display applications in the next generation. This paper introduces a femtosecond laser‐induced forward transfer (FsLIFT) technology that integrates deposition pattern and alignment in a single transfer step. This development enables the fabrication of high‐resolution full‐color QD films. The ability of FsLIFT to precisely locate red, green, and blue QDs in a designated position allows to obtain arbitrarily shaped full‐color patterns and pixel arrays with a resolution of 1.78 µm. In addition, the potential for optoelectronic devices is ensured by the preserved photophysical properties, high smoothness, and continuity of the transferred QD films. Consequently, the light‐emitting diodes (LEDs) are successfully fabricated based on the transferred QD films. This study expects that the introduced straightforward patterning technology, offering high freedom, precision, and repeatability, will contribute to advancing the development of full‐color high‐resolution displays based on QDs.

Improved Single-Shot Qubit Readout Using Twin rf-SET Charge Correlations

High-fidelity qubit readout is critical in order to obtain the thresholds needed to implement quantum error-correction protocols and achieve fault-tolerant quantum computing. Large-scale silicon qubit devices will have densely packed arrays of quantum dots with multiple charge sensors that are, on average, farther away from the quantum dots, entailing a reduction in readout fidelities. Here, we present a readout technique that enhances the readout fidelity in a linear SiMOS four-dot array by amplifying correlations between a pair of single-electron transistors, known as a twin SET. By recording and subsequently correlating the twin SET traces as we modulate the dot detuning across a charge transition, we demonstrate a reduction in the charge readout infidelity by over one order of magnitude compared to traditional readout methods. We also study the spin-to-charge conversion errors introduced by the modulation technique and conclude that faster modulation frequencies avoid relaxation-induced errors without introducing significant spin-flip errors, favoring the use of the technique at short integration times. This method not only allows for faster and higher-fidelity qubit measurements but it also enhances the signal corresponding to charge transitions that take place farther away from the sensors, enabling a way to circumvent the reduction in readout fidelities in large arrays of qubits. Published by the American Physical Society 2024

Continuous wave laser fabrication of small pitch/size perovskite pixels realizes high-resolution color conversion micro-LED displays.

As a new generation of display technology, micro-light-emitting diodes (micro-LEDs) have been widely recognized owing to their excellent performance in brightness, contrast ratio, resolution, etc. This work proposes a continuous wave (CW) laser writing strategy to achieve perovskite quantum dots (PQDs) array with small pixel size and pitch, overcoming the processing difficulties and limitations of mass transfer. Since PQDs have highly dynamic surface ligand states and low ionic bond energy, suitable laser power can quench PQDs and form an array area. The use of low-power CW lasers in the laser direct writing process, on the one hand, greatly maintains the luminescence performance and edge flatness of each PQD array, and the pixel pitch (1.5 μm-9 μm)/size can be adjusted arbitrarily, which meets the high-resolution micro-display requirements. On the other hand, we found that after the low-power laser quenches the PQDs, its residual oxide can absorb photons, thus reducing the backlight leakage in color conversion micro-LEDs. Finally, red/green/blue three-color conversion micro-LED and laser projection displays were realized; these results provide a feasible strategy for next-generation micro-LED displays.

Investigation of p- and n-Type Quantum Dot Arrays Manufactured in 22nm FDSOI CMOS at 2-4 K and 300 K

Investigation of <i>p</i>- and <i>n</i>-Type Quantum Dot Arrays Manufactured in 22nm FDSOI CMOS at 2-4 K and 300 K

Direct in situ photolithography of ultra-stable CsPbBr3 quantum dot arrays based on crosslinking polymerization.

CsPbX3 (X = Br, Cl, I) perovskite quantum dots (PQDs) are the rising star for various display applications owing to their excellent opto-electrical properties, such as an adjustable spectrum, narrow emission linewidth and high quantum yield. However, these PQDs are well known to suffer from intrinsic instability under atmospheric conditions. In this work, a novel photosensitive ligand, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (XBPO), was employed as a dual-functional reagent for PQD surface engineering. The XBPO ligand could cleave to produce phenylphosphinyl radicals and trimethylbenzoyl radicals under UV light irradiation. The phenylphosphinyl radicals with PO bonds could effectively passivate the PQD surface defects, leading to quantum yield improvement. The CsPbBr3 and CsPbI3 PQDs with XBPO modification could achieve a photoluminescence quantum yield (PLQY) of near unity and 92%, respectively. Additionally, the in situ encapsulation of the PQDs was achieved by the subsequent crosslinking polymerization, which significantly improved the stability of the PQDs against solvents and the environment. By combining a standard photolithography procedure, we demonstrated a micro-pattern of CsPbBr3 PQDs. These results establish a universal route for PQD patterning, compatible with the existing photolithography processes, which could facilitate the application of PQDs in next-generation display technology.

Capacitive crosstalk in gate-based dispersive sensing of spin qubits

In gate-based dispersive sensing, the response of a resonator attached to a quantum dot gate is detected by a reflected radio frequency signal. This enables fast readout of spin qubits and tune up of arrays of quantum dots but comes at the expense of increased susceptibility to crosstalk, as the resonator can amplify spurious signals and induce fluctuations in the quantum dot potential. We attach tank circuits with superconducting NbN inductors and internal quality factors Qi&amp;gt;1000 to the interdot barrier gate of silicon double quantum dot devices. Measuring the interdot transition in transport, we quantify radio frequency crosstalk that results in a ring-up of the resonator when neighboring plunger gates are driven with frequency components matching the resonator frequency. This effect complicates qubit operation and scales with the loaded quality factor of the resonator, the mutual capacitance between device gate electrodes, and with the inverse of the parasitic capacitance to ground. Setting qubit frequencies below the resonator frequency is expected to substantially suppress this type of crosstalk.

Single-electron routing in a silicon quantum-dot array

Single-electron routing in a silicon quantum-dot array

Readout using resonant tunneling in silicon spin qubits

Spin qubit systems are one of the promising candidates for quantum computing. The quantum dot (QD) arrays are intensively investigated by many researchers. Because the energy-difference between the up-spin and down-spin states is very small, the detection of the qubit state is of prime importance in this field. Moreover, many wires are required to control qubit systems. Therefore, the integration of qubits and wires is also an important issue. In this study, the measurement process of QD arrays is theoretically investigated using resonant tunneling, controlled by a conventional transistor. It is shown that the number of possible measurements during coherence time can exceed a hundred under the backaction of the measurements owing to the nonlinear characteristics of resonant tunneling. It is also discussed to read out the measurement results by the conventional transistor.

Peculiarities of Growth of InAs Quantum Dot Arrays with Low Surface Density by Molecular Beam Epitaxy

Peculiarities of Growth of InAs Quantum Dot Arrays with Low Surface Density by Molecular Beam Epitaxy

Investigation of the Photoelectric Characteristics of GaAs Solar Cells with Different InGaAs Quantum Dot Array Positioning in the i-Region

Investigation of the Photoelectric Characteristics of GaAs Solar Cells with Different InGaAs Quantum Dot Array Positioning in the i-Region

Cryogenic multiplexing using selective area grown nanowires

Bottom-up grown nanomaterials play an integral role in the development of quantum technologies but are often challenging to characterise on large scales. Here, we harness selective area growth of semiconductor nanowires to demonstrate large-scale integrated circuits and characterisation of large numbers of quantum devices. The circuit consisted of 512 quantum devices embedded within multiplexer/demultiplexer pairs, incorporating thousands of interconnected selective area growth nanowires operating under deep cryogenic conditions. Multiplexers enable a range of new strategies in quantum device research and scaling by increasing the device count while limiting the number of connections between room-temperature control electronics and the cryogenic samples. As an example of this potential we perform a statistical characterization of large arrays of identical quantum dots thus establishing the feasibility of applying cross-bar gating strategies for efficient scaling of future selective area growth quantum circuits. More broadly, the ability to systematically characterise large numbers of devices provides new levels of statistical certainty to materials/device development.

The effect of 1 MeV electron irradiation on charge carrier localization in graphene quantum dot array of reduced graphene oxide

This paper presents a study of the effect of 1 MeV electron irradiation on the localization of charge carriers in graphene quantum dots (GQDs) located in a reduced graphene oxide (RGO). The electrical properties were analyzed in a wide temperature range of 4.2–340 K for fluences of 0–160 × 1015 cm−2. The localization length, dielectric permittivity, and density of localized states were estimated. It was found that the conductivity and charge localization parameters exhibit non-monotonic behavior depending on the electron fluences. It can change several times in the vicinity of a fluence of 10 × 1015 cm−2 compared to the higher or lower fluence. It is shown that electron irradiation affects the disordered surrounding matrix, which leads to an increase in the content of oxygen and functional groups. At the same time, the size of the sp2‑carbon domains does not depend on the fluence. It is assumed that electron irradiation indirectly affects the properties of GQDs. The transformation of the surrounding disordered matrix leads to a modification of the electronic properties of the GQDs array and the RGO as a whole. The non-monotonic behavior of the RGO conductivity upon irradiation is due to the features of the energy spectrum of the GQDs array, which is characterized by the presence of periodic peaks in the density of states. The irradiation-induced structural modification likely leads to a shift in the Fermi level and a change in the density of states. It is shown that the RGO behaves like a wide-band doped semiconductor. The difference is that the impurity level was formed by GQDs. At temperatures above 310 K, the RGO conductivity exhibits an Arrhenius behavior with an activation energy of about 60 meV due to charge carrier delocalization at thermal ejection into the extended band.

Nagaoka ferromagnetism in an array of phosphorene quantum dots.

We consider an array of four quantum dots defined in phosphorene containing three excess electrons, i.e., in the conditions of near half filling when itinerant Nagaoka ferromagnetism is expected to appear in a square array with isotropic interdot hopping. The interdot hopping in the array arranged in a square inherits the anisotropy from the form of the phosphorene conduction band. We apply the configuration interaction method for discussion of the appearance and stability of the spin-polarized ground state and discuss the compensation of the effective mass anisotropy by the geometry of the quantum dot array. Our study shows strong stability of Nagaoka ferromagnetism for optimized geometry of the array, with the Nagaoka gap as large as ∼230µeV. A phase diagram for the ground-state spin ordering versus the geometric parameters of the array is presented. We study the suppression of the ferromagnetism in a transition of the [Formula: see text] array to a quasi-1D chain and indicate that the shift of one of the quantum dots away from the array center is enough to transform the system to a quantum dot chain. A shift in the zigzag crystal direction induces the low-spin ground state more effectively than a shift along the armchair direction. We also discuss the robustness of the spin ordering against detuning one of the dots. The ferromagnetic ground-state survives as long as the detuning is not large enough to trap one of the electrons within a single quantum dot (for positive detuning) or remove one of the quantum dots of the accessible energy range (for negative detuning).