Coupled Double Quantum Dots Research Articles

Coupled vertical double quantum dots at single-hole occupancy

Gate-defined quantum dots define an attractive platform for quantum computation and have been used to confine individual charges in a planar array. Here, we demonstrate control over vertical double quantum dots confined in a strained germanium double quantum well. We sense individual charge transitions with a single-hole transistor. The vertical separation between the quantum wells provides a sufficient difference in capacitive coupling to distinguish quantum dots located in the top and bottom quantum wells. Tuning the vertical double quantum dot to the (1,1) charge state confines a single-hole in each quantum well beneath a single plunger gate. By simultaneously accumulating holes under two neighboring plunger gates, we are able to tune to the (1,1,1,1) charge state. These results motivate quantum dot systems that exploit the third dimension, opening new opportunities for quantum simulation and quantum computing.

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.

Global Quantum Discord and Entanglement in two Coupled Double Quantum Dots AlGaAs/GaAs

Global Quantum Discord and Entanglement in two Coupled Double Quantum Dots AlGaAs/GaAs

Heat Capacity of Two Interacting Electrons in Coupled Double Quantum Dots

Heat Capacity of Two Interacting Electrons in Coupled Double Quantum Dots

Theoretical Treatment for Spin-Polarized Current Through Serially Coupled Double Quantum Dots: The Coherent Tunneling Effect

Theoretical Treatment for Spin-Polarized Current Through Serially Coupled Double Quantum Dots: The Coherent Tunneling Effect

Thermal Entanglement and Correlated Coherence in Two Coupled Double Quantum Dots Systems

AbstractIn this work, the thermal quantum correlations in two coupled double semiconductor charge qubits are investigated. This is carried out by deriving analytical expressions for both the thermal concurrence and the correlated coherence. The effects of the tunneling parameters, the Coulomb interaction, and the temperature on the thermal entanglement and on the correlated coherence are studied in detail. It is found that the Coulomb potential plays an important role in the thermal entanglement and in the correlated coherence of the system. The results also indicate that the Coulomb potential can be used for significant enhancement of the thermal entanglement and quantum coherence. One interesting aspect is that the correlated coherence capture all the thermal entanglement at low temperatures, that is, the local coherences are totally transferred to the thermal entanglement. Finally, the role played by thermal entanglement and the correlated coherence responsible for quantum correlations are focused on. It is shown that in all cases, the correlated coherence is more robust than the thermal entanglement so that quantum algorithms based only on correlated coherence may be more robust than those based on entanglement.

Analytic treatment of the thermoelectric properties for two coupled quantum dots threaded by magnetic fields

Coupled double quantum dots (c-2QD) connected to leads have been widely adopted as prototype model systems to verify interference effects on quantum transport at the nanoscale. We provide here an analytic study of the thermoelectric properties of c-2QD systems pierced by a uniform magnetic field. Fully analytic and easy-to-use expressions are derived for all the kinetic functionals of interest. Within the Green’s function formalism, our results allow a simple inexpensive procedure for the theoretical description of the thermoelectric phenomena for different chemical potentials and temperatures of the reservoirs, different threading magnetic fluxes, dot energies and interdot interactions; moreover they provide an intuitive guide to parametrize the system Hamiltonian for the design of best performing realistic devices. We have found that the thermopower S can be enhanced by more than ten times and the figure of merit ZT by more than hundred times by the presence of a threading magnetic field. Most important, we show that the magnetic flux increases also the performance of the device under maximum power output conditions.

Sub-Poissonian photon emission in coupled double quantum dots–cavity system**Project supported by the National Natural Science Foundation of China (Grant Nos. 61372037 and 61401035), the Beijing Excellent Ph.D. Thesis Guidance Foundation, China (Grant No. 20131001301), and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), China (Grant No. IPOC2015ZC05).

In this work, we theoretically analyze the few-photon emissions generated in a coupled double quantum dots (CDQDs)-single mode microcavity system, under continuous wave and pulse excitation. Compared with the uncoupled case, strong sub-Poissonian character is achieved in a CDQDs–cavity system at a certain laser frequency. Based on the proposed scheme, single photon generation can be obtained separately under QD–cavity resonant condition and off-resonant condition. For different cavity decay rates, we reveal that laser frequency detunings of minimum second-order autocorrelation function are discrete and can be divided into three regions. Moreover, the non-ideal situation where two QDs are not identical is discussed, indicating the robustness of the proposed scheme, which possesses sub-Poissonian character in a large QD difference variation range.

Current Rectification and Seebeck Coefficient of Serially Coupled Double Quantum Dots

The transport properties of serially coupled quantum dots (SCQDs) embedded in a matrix connected to metallic electrodes are theoretically studied in the linear and nonlinear regimes. The current rectification and negative differential conductance of SCQDs under the Pauli spin blockade condition are attributed to the combination of bias-direction dependent probability weight and off-resonant energy levels yielded by the applied bias across the junctions. We observe the spin-polarization current rectification under the Zeeman effect. The maximum spin-polarization current occurs in the forward bias regime. Such behavior is different from the charge current rectification. Finally, the Seebeck coefficient (S) of SCQDs is calculated and analyzed in the cases without and with electron phonon interactions. The application of SCQDs as a temperature detector is discussed on the basis of the nonlinear behavior of S with respect to temperature difference across the junction.

Kondo Effect Versus Magnetic Coupling in Indirectly Coupled Double Quantum Dots

We theoretically investigate a device consisting of two quantum dots (QDs) side-coupled to a quantum wire which has many physical ingredients of an artificial heavy fermion system. An extra parameter, the distance L between the two QDs, is introduced and it plays an important role on the competition of the Kondo temperature and magnetic coupling. Three different phases are found: antiferromagnetic phase, Kondo phase with spin S = 1/2, and Kondo phase with S = 1, depending on the distance L, the magnetic coupling, and the Kondo temperature. Quantum transport properties are qualitatively different for different phases: for the S = 1 Kondo and the antiferromagnetic phases, the conductance tends to the unitary value 2e2/h; for the S = 1/2 Kondo phase the conductance is strongly dependent on the distance.

Large Nuclear Overhauser Fields Detected in Vertically Coupled Double Quantum Dots

We report the electrical induction and detection of dynamic nuclear polarization in the spin-blockade regime of double GaAs vertical quantum dots. The nuclear Overhauser field measurement relies on bias voltage control of the interdot spin exchange coupling and measurement of dc current at variable external magnetic fields. The largest Overhauser field observed was about 4 T, corresponding to a nuclear polarization approximately 40% for the electronic g factor typical of these devices, |g*| approximately 0.25. A phenomenological model is proposed to explain these observations.

Quantum Phase Transition in Capacitively Coupled Double Quantum Dots

We investigate two equivalent, capacitively coupled semiconducting quantum dots, each coupled to its own lead, in a regime where there are two electrons on the double dot. With increasing interdot coupling, a rich range of behavior is uncovered: first a crossover from spin- to charge-Kondo physics, via an intermediate SU(4) state with entangled spin and charge degrees of freedom, followed by a quantum phase transition of Kosterlitz-Thouless type to a non-Fermi-liquid "charge-ordered" phase with finite residual entropy and anomalous transport properties. Physical arguments and numerical renormalization group methods are employed to obtain a detailed understanding of the problem.

Quantum rate equations for electron transport through an interacting system in the sequential tunneling regime

We present a set of modified quantum rate equations, with the help of the nonequilibrium Green's function and slave-particle techniques along with the correct quantization, for description of the quantum transport through an interacting mesoscopic region connected with two leads, in the sequential tunneling regime. The assumption that only leading order of $|V|^2$ ($V$ is the tunneling coupling between the interacting central region and the leads) has been taken into account in deriving these equations implies that the quantum rate equations are only valid in the case of weak coupling between the central region and the leads. For demonstrations, we consider two special cases in the central region, a single interacting quantum dot (SQD) with weak spin-flip scattering and a weakly coupled double quantum dots (CQD), as examples. In the limit of zero temperature and large bias voltage, the resulting equations are identical to the previous results derived from the many-body Schr\"odinger equation. The numerical simulations reveal: 1) the dependence of the spin-flip scattering on the temperature and bias voltage in the SQD; and 2) the possible negative differential conductance and negative tunnel magnetoresistance in the CQD, depending on the hopping between the two quantum dots.

Strain-induced quantum dot superlattice

Coupled double quantum dots and quantum dot superlattices are formed by utilizing the strain of an InP island on top of a near-surface multi-quantum-well structure. The number and composition of the quantum wells together with the thickness of the barrier separating the quantum wells are varied to investigate the coupling of the wave functions of the carriers confined in separate vertically stacked dots. Photoluminescence studies show that the reduction of the barrier thickness and the increase of the number of wells enhance the coupling, which is observed as red shift and narrowing of the quantum dot peak. The calculated shifts of the peak positions agree closely with the experimental values.