Double Quantum Dot Research Articles

Composed Effects of Electron-Hole Exchange and Near-Field Interaction in Quantum-Dot-Confined Radiative Dipoles

Conservation of polarization is an important requirement for reliable single-photon emitters, which, in turn, are essential building blocks for light-based quantum information processing. In this work, we study the exciton-spin dynamics in a double quantum dot under the combined effects of electron-hole exchange and Förster resonance energy transfer. By means of numerical solutions of the quantum master equation, we simulate the time-dependent spin polarization for two neighboring dots. According to our results, under some conditions, the depolarization caused by the electron-hole exchange may be slowed by the near field-induced interdot energy transfer, suggesting a new mechanism to extend the exciton coherence time. This opens doors to alternative schemes for improved solid-state quantum light sources.

Double quantum dots in atomically-precise graphene nanoribbons

Bottom-up synthesized graphene nanoribbons (GNRs) are precise quantum materials, offering a high degree of tunability of their physical properties. While field-effect transistors and single quantum dot (QD) devices have been reported, the fabrication of double QD devices using GNRs remains challenging due to their nanometer-scale dimensions. In this study, we present a multi-gate double QD device based on atomically precise GNRs that are contacted by a pair of single-walled carbon nanotube electrodes. At low temperatures, the device can be tuned with multiple gates and reveals triangular features characteristic for charge transport through a double QD system. From these features, the QD level spacing, as well as the interdot tunnel coupling and lead-dot tunnel couplings are extracted. Double QD systems serve as essential building blocks for developing different types of qubits based on atomically precise GNRs.

Dispersive readout of a silicon quantum device using an atomic force microscope-based rf gate sensor

We demonstrate dispersive charge sensing of Si/SiGe single and double quantum dots by coupling sub-micron floating gates to a radio frequency reflectometry (rf-reflectometry) circuit using the tip of an atomic force microscope. Charge stability diagrams are obtained in the phase response of the reflected rf signal. We demonstrate single-electron dot-to-lead and dot-to-dot charge transitions with a signal-to-noise ratio (SNR) of 2 and integration time of τ=2.7 ms and τ=6.4 ms, respectively. The charge sensing SNR compares favorably with results obtained on conventional devices. Moreover, the small size of the floating gates largely eliminates the coupling to parasitic charge traps that can complicate the interpretation of the dispersive charge sensing data.

Shared control of a 16 semiconductor quantum dot crossbar array

The efficient control of a large number of qubits is one of the most challenging aspects for practical quantum computing. Current approaches in solid-state quantum technology are based on brute-force methods, where each and every qubit requires at least one unique control line—an approach that will become unsustainable when scaling to the required millions of qubits. Here, inspired by random-access architectures in classical electronics, we introduce the shared control of semiconductor quantum dots to efficiently operate a two-dimensional crossbar array in planar germanium. We tune the entire array, comprising 16 quantum dots, to the few-hole regime. We then confine an odd number of holes in each site to isolate an unpaired spin per dot. Moving forward, we demonstrate on a vertical and a horizontal double quantum dot a method for the selective control of the interdot coupling and achieve a tunnel coupling tunability over more than 10 GHz. The operation of a quantum electronic device with fewer control terminals than tunable experimental parameters represents a compelling step forward in the construction of scalable quantum technology.

Bound states in the continuum and Majorana zero modes in a double quantum dot interferometer: Ghost-Fano Majorana effect

Bound states in the continuum and Majorana zero modes in a double quantum dot interferometer: Ghost-Fano Majorana effect

Design space of quantum dot spin qubits

Solid-state qubits can be implemented with electrostatically confined quantum dots in semiconductors, allowing gate voltages to independently control the electrochemical potentials of each quantum dot. Quantum dots offer high levels of reliability and scalability. In this paper, along with our proposed approach based on the Generalized Hubbard model followed by Fermi’s Golden rule, the charge stability diagram of a double quantum dots system with two electrons has been studied extensively. The validity of the presented approach is confirmed by experimental data. Using Fermi’s Golden rule for mapping the charge stability diagram, we have deeply studied the temperature effects arising from both the Hamiltonian and transport. In addition, spin-exchange, pair-hopping, and the occupation-modulated hopping parameters on the states of the charge stability diagram are deeply discussed. Furthermore, we incorporate the Zeeman energies in the Hubbard model in order to theoretically study the spin splitting caused by an external magnetic field applied to the quantum dots. In particular, the aim of this paper is to rely on fundamental physical concepts in order to model and optimize the singlet–triplet qubit in quantum dots. In this study, the probabilities associated with singlet and triplet states have been modeled and analyzed under the impacts of intrinsic and extrinsic parameters. This will help us to find the optimal condition for coupling between double dots and provides us the design rules in terms of physical parameters to efficiently design, measure and sense, initialize, manipulate, and readout of the qubit state.

Charge-sensing of a Ge/Si core/shell nanowire double quantum dot using a high-impedance superconducting resonator

Spin qubits in germanium are a promising contender for scalable quantum computers. Reading out of the spin and charge configuration of quantum dots formed in Ge/Si core/shell nanowires is typically performed by measuring the current through the nanowire. Here, we demonstrate a more versatile approach on investigating the charge configuration of these quantum dots. We employ a high-impedance, magnetic-field resilient superconducting resonator based on NbTiN and couple it to a double quantum dot in a Ge/Si nanowire. This allows us to dispersively detect charging effects, even in the regime where the nanowire is fully pinched off and no direct current is present. Furthermore, by increasing the electro-chemical potential far beyond the nanowire pinch-off, we observe indications for depleting the last hole in the quantum dot by using the second quantum dot as a charge sensor. This work opens the door for dispersive readout and future spin-photon coupling in this system.

Spectral Response of a Microresonator Containing a Double Quantum Dot Modified by Coulomb Interaction of Localized Electrons

Spectral Response of a Microresonator Containing a Double Quantum Dot Modified by Coulomb Interaction of Localized Electrons

Tunneling magnetoresistance calculation for double quantum dot connected in parallel shape to ferromagnetic Leads

In this paper, a theoretical model for electron transport through symmetric system consisting of two baths interferometer with one single-level quantum dot in each of its arms was considered. In this model, the dots are attached to ferromagnetic leads with parallel and antiparallel magnetic configurations. Green's function technique in this model was used. Our focus is on the Transport characteristics of conductance (G) and tunnel magnetoresistance (TMR). A special attention to the influence of an applied magnetics flux on the characteristics of conductance and tunneling magnetoresistance was paid. Concerning the study of the conductance, it was found that the effect of bonding (antibonding) states is most obvious in quantum dots at various values of the magnetic field. The change in spin-polarization value was seen to affect the increase and decrease in the conductance value. We noticed a difference in calculation of TMR in the bonding and the antibonding states, where the results show Strong dissonance in bonding state and strong attraction in antibonding state.

Applications of Hybrid Metal Nanoparticle-Quantum Dot in Biomedical Applications

Nanomaterials are at the forefront of the fast-paced development of nanotechnology. These materials are outstanding and indispensable in various human activities as long as their size-dependent characteristics. One of the most promising applications of nanomaterials is biomedical. This work reviews the hybrid quantum dot-metal nanoparticle applications in biomedical. An analytical model for the double quantum dot

In situ growth of Bi/Ag double quantum dots on hollow Bi2MoO6 microspheres: Enhancement of the surface plasmon resonance effect on PMS activation

In this work, the effect of Bi/Ag double quantum dots on plasmon resonance and PMS activation was investigated. Bi/Ag double quantum dots were generated in situ on hollow Bi2MoO6 microspheres by stepwise irradiation using a high-energy β electron beam. The formation of Bi/Ag DQDs greatly optimized the drawbacks of Bi2MoO6 in terms of light absorption. Synergistic introduction of DQDs greatly reduced the band gap from 2.72 eV to 2.12 eV. The Bi−Ag@Bi2MoO6 − 400/PMS system degraded ciprofloxacin with kinetic constants 10 and 12 times higher than those of the Bi@Bi2MoO6/PMS and Bi2MoO6/PMS systems. The formation of an electron transfer path from Ag QDs to Bi QDs enhanced the SPR effect of Bi QDs.·O2− and 1O2 played a major role in the CIP degradation process. This study will provide a new strategy for enhancing the Bi plasmon resonance effect and provide a technical method to the efficient degradation of antibiotics in water.

Probing Two Driven Double Quantum Dots Strongly Coupled to a Cavity.

We experimentally and theoretically study a driven hybrid circuit quantum electrodynamics (cQED) system beyond the dispersive coupling regime. Treating the cavity as part of the driven system, we develop a theory applicable to such strongly coupled and to multiqubit systems. The fringes measured for a single driven double quantum dot (DQD)-cavity setting and the enlarged splittings of the hybrid Floquet states in the presence of a second DQD are well reproduced with our model. This opens a path to study Floquet states of multiqubit systems with arbitrarily strong coupling and reveals a new perspective for understanding strongly driven hybrid systems.

Entanglement and thermokinetic uncertainty relations in coherent mesoscopic transport

A deeper understanding of the differences between quantum and classical dynamics promises great potential for emerging technologies. Nevertheless, some aspects remain poorly understood, particularly concerning the role of quantum coherence in open quantum systems. On the one hand, coherence leads to entanglement and even nonlocality. On the other, it may lead to a suppression of fluctuations, causing violations of thermo-kinetic uncertainty relations (TUR and KUR) that are valid for classical processes. These represent two different manifestations of coherence, one depending only on the state of the system (static) and one depending on two-time correlation functions (dynamical). Here we employ these manifestations of coherence to determine when mesoscopic quantum transport can be captured by a classical model based on stochastic jumps, and when such a model breaks down, implying nonclassical behavior. To this end, we focus on a minimal model of a double quantum dot coupled to two thermal reservoirs. In this system, quantum tunneling induces Rabi oscillations and results in both entanglement and nonlocality, as well as TUR and KUR violations. These effects, which describe the breakdown of a classical description, are accompanied by a peak in coherence. Our results provide guiding principles for the design of out-of-equilibrium devices that exhibit nonclassical behavior.

A vertical gate-defined double quantum dot in a strained germanium double quantum well

A vertical gate-defined double quantum dot in a strained germanium double quantum well

Wigner-molecularization-enabled dynamic nuclear polarization

Multielectron semiconductor quantum dots (QDs) provide a novel platform to study the Coulomb interaction-driven, spatially localized electron states of Wigner molecules (WMs). Although Wigner-molecularization has been confirmed by real-space imaging and coherent spectroscopy, the open system dynamics of the strongly correlated states with the environment are not yet well understood. Here, we demonstrate efficient control of spin transfer between an artificial three-electron WM and the nuclear environment in a GaAs double QD. A Landau–Zener sweep-based polarization sequence and low-lying anticrossings of spin multiplet states enabled by Wigner-molecularization are utilized. Combined with coherent control of spin states, we achieve control of magnitude, polarity, and site dependence of the nuclear field. We demonstrate that the same level of control cannot be achieved in the non-interacting regime. Thus, we confirm the spin structure of a WM, paving the way for active control of correlated electron states for application in mesoscopic environment engineering.

Molecularly imprinted polymers embedded with double perovskite quantum dots: A ratiometric fluorescence sensor for visible and fluorescent determination of Rhein

A ratiometric fluorescence sensor based on molecularly imprinted polymers embedded with double perovskite quantum dots (green fluorescent CsPbBr3 (GPQDs) and red fluorescent CsPbI3 (RPQDs)) were prepared for the visible and fluorescent determination of Rhein. Double perovskite quantum dots were synthesized by a one-pot method with in-situ hydrolysis, and the fluorescent probes containing GPQDs and RPQDs with molecularly imprinted cavities (MIPs@RPQDs/GPQDs@SiO2) were synthesized by sol gel method. And the synthesized MIPs@RPQDs/GPQDs@SiO2 can emit two stable and independent fluorescence peaks at 520 nm with green fluorescence and at 695 nm with red fluorescence respectively. Since Rhein could specifically quench the red fluorescence without affecting the green fluorescence at 520 nm, a ratiomitric fluorescence sensor could be and was constructed with GPQDs as the internal standard signal and the RPQDs as the response signal. The sensor had a good linear relationship with the concentration of Rhein between 15 and 135 nM, and the detection limit was 1.90 nM (S/N = 3). Moreover, Rhein could be detected by observing the color transformation of the fluorescent probe directly with naked eyes. In addition, Rhein in the traditional Chinese medicine Rheum palmatum L. had been detected by the constructed ratiometric fluorescene probe with satisfactory.

Thermal entanglement and quantum coherence of a single electron in a double quantum dot with Rashba interaction

In this work, we study the thermal quantum coherence and fidelity in a semiconductor double quantum dot. The device consists of a single electron in a double quantum dot with Rashba spin-orbit coupling in the presence of an external magnetic field. In our scenario, the thermal entanglement of the single electron is driven by the charge and spin qubits, the latter controlled by Rashba coupling. Analytical expressions are obtained for thermal concurrence and correlated coherence using the density matrix formalism. The main goal of this work is to provide a good understanding of the effects of temperature and several parameters in quantum coherence. In addition, our findings show that we can use the Rashba coupling to tune in the thermal entanglement, quantum coherence, as well as, the thermal fidelity behavior of the system. Moreover, we focus on the role played by thermal entanglement and correlated coherence responsible for quantum correlations. We observe that the correlated coherence is more robust than the thermal entanglement in all cases, so quantum algorithms based only on correlated coherence may be stronger than those based on entanglement.

Majorana tunneling in a non-Hermitian double-quantum-dot structure

In this paper, we investigate a non-Hermitian quantum transport system, which is formed by two quantum dots possessing PT-symmetric complex potentials and side coupled to Majorana fermions. We study the transmission coefficient first. It is found that the conductance is reduced by a factor of 1/4, i.e., G=e2/4h, which can be seen as a signature of Majorana fermion in this double quantum dots structure. It is also found that the joint effects of Majorana tunneling, PT-symmetric complex potentials and dot energy level are mainly as follows: merging process, asymmetry and exceptional point. Then we study the current and conductance driven by a voltage or temperature gradient. Due to the merging process and asymmetry, the thermal current and conductance change sign drastically near the exceptional point. With large fixed temperature difference, the relationship between thermal current and dot level becomes linear, which is a manifestation of Majorana fermion’s robustness. These results can be useful in understanding the quantum transport behaviors modified by the interplay between PT symmetry and Majorana fermions.

Photo-assisted spin transport in double quantum dots with spin–orbit interaction

We investigate the effect of spin–orbit interaction on the intra- and interdot particle dynamics of a double quantum dot (QD) under ac electric fields. The former is modeled as an effective ac magnetic field that produces electric-dipole spin resonance transitions, while the latter is introduced via spin-flip tunneling amplitudes. We observe the appearance of non-trivial spin-polarized dark states (DSs), arising from an ac-induced interference between photo-assisted spin-conserving and spin-flip tunneling processes. These DSs can be employed to precisely measure the spin–orbit coupling in QD systems. Furthermore, we show that the interplay between photo-assisted transitions and spin-flip tunneling enables the system to operate as a highly tunable spin filter. Finally, we investigate the operation of the system as a resonant flopping-mode qubit for arbitrary ac voltage amplitudes, allowing for high tunability and enhanced qubit control possibilities.

Quench dynamics of Fano-like resonances in the presence of the on-dot superconducting pairing

We explore the electron dynamics of a system composed of double quantum dot embedded between metallic and superconducting leads in a “T-shape” geometry. In nanoscopic systems, where electron transfer between electrodes can be realized via different paths, interference effects play an important role. For double quantum dot system in the chosen geometry, interference of electrons transferred between electrodes via the interfacial quantum dot and electrons scattered on the side dot gives rise to Fano-like interference. If such a system is additionally coupled to a superconducting electrode, together with the well-understood Fano resonance an additional resonance appears on the opposite side of the Fermi level. In the recent work (Barański et al. in Sci Rep 10:2881, 2020), we showed that this resonance occurs solely as a result of the local pairing of non-scattered electrons with scattered ones. In this work, considering the quench dynamics, we explore how much time is required for formation of each of these resonances. In particular, (i) we analyze the charge oscillations between subsystems; (ii) we estimate the time required for each resonance to achieve stable equilibrium upon an abrupt change of interdot connection; (iii) we discuss a typical energy and time scales for experiments on similar architectures.