Coherent manipulation of electronic States in a double quantum dot

We investigate coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot. This fully tunable qubit is manipulated with a high-speed voltage pulse that controls the energy and decoherence of the system. Coherent oscillations of the qubit are observed for several combinations of many-body ground and excited states of the quantum dots. Possible decoherence mechanisms in the present device are also discussed.     

Coherent single electron spin control in a slanting Zeeman field

We consider a single electron in a 1D quantum dot with a static slanting Zeeman field. By combining the spin and orbital degrees of freedom of the electron, an effective quantum two-level (qubit) system is defined. This pseudospin can be coherently manipulated by the voltage applied to the gate electrodes, without the need for an external time-dependent magnetic field or spin-orbit coupling. Single-qubit rotations and the controlled-NOT operation can be realized. We estimated the relaxation (T1) and coherence (T2) times and the (tunable) quality factor. This scheme implies important experimental advantages for single electron spin control.     

Observation of collapse of pseudospin order in bilayer quantum Hall ferromagnets

The Hartree-Fock paradigm of bilayer quantum Hall states with finite tunneling at filling factor nu=1 has full pseudospin ferromagnetic order with all the electrons in the lowest symmetric Landau level. Inelastic light scattering measurements of low energy spin excitations reveal major departures from the paradigm at relatively large tunneling gaps. The results indicate the emergence of a novel correlated quantum Hall state at nu=1 characterized by reduced pseudospin order. Marked anomalies occur in spin excitations when pseudospin polarization collapses by application of in-plane magnetic fields.     

Realization of the SU(N) Kondo effect in a strong magnetic field

In this Letter we suggest a realization of the SU(N) Kondo effect, using quantum dots at strong magnetic field. We propose using edge states of the quantum Hall effect as pseudospin that interact with multiple quantum dots structures. In the suggested realization one can access each pseudospin separately and hence may perform a set of experiments that were impossible until now. We focus on the realization of SU(2) and SU(3) Kondo effects and find in the unitary limit a conductivity of 3/4 quantum conductance in the SU(3) case.     

Phase diagram for quantum hall bilayers at nu=1

We present a phase diagram for a double quantum well bilayer electron gas in the quantum Hall regime at a total filling factor nu=1, based on exact numerical calculations of the topological Chern number matrix and the (interlayer) superfluid density. We find three phases: a quantized Hall state with pseudospin superfluidity, a quantized Hall state with pseudospin "gauge-glass" order, and a decoupled composite Fermi liquid. Comparison with experiments provides a consistent explanation of the observed quantum Hall plateau, Hall drag plateau, and vanishing Hall drag resistance, as well as the zero-bias conductance peak effect, and suggests some interesting points to pursue experimentally.     

Exact Pseudospin Symmetric Solution of the Dirac Equation for Pseudoharmonic Potential in the Presence of Tensor Potential

Under the pseudospin symmetry, we obtain exact solution of the Dirac equation for the pseudoharmonic potential in the presence of the tensor potential with arbitrary spin–orbit coupling quantum number κ. The energy eigenvalue equation of the Dirac particles is found and the corresponding radial wave functions are presented in terms of confluent hypergeometric functions. We investigate the tensor potential dependence of the energy of the each state in the pseudospin doublet. It is shown that degeneracy between members of the pseudospin doublet is removed by tensor interaction. Furthermore, the radial node structure of the Dirac spinor is discussed.     

Pseudospin symmetric solutions of the Dirac equation with the modified Rosen—Morse potential using Nikiforov—Uvarov method and supersymmetric quantum mechanics approach

Employing the Pekeris-type approximation to deal with the pseudo-centrifugal term, we analytically study the pseudospin symmetry of a Dirac nucleon subjected to equal scalar and vector modified Rosen-Morse potential including the spin-orbit coupling term by using the Nikiforov-Uvarov method and supersymmetric quantum mechanics approach. The complex eigenvalue equation and the total normalized wave functions expressed in terms of Jacobi polynomial with arbitrary spin-orbit coupling quantum number k are presented under the condition of pseudospin symmetry. The eigenvalue equations for both methods reproduce the same result to affirm the mathematical accuracy of analytical calculations. The numerical solutions obtained for different adjustable parameters produce degeneracies for some quantum number.     

Dirac equation for the Hulthén potential within the Yukawa-type tensor interaction

Using the Nikiforov-Uvarov (NU) method, pseudospin and spin symmetric solutions of the Dirac equation for the scalar and vector Hulthén potentials with the Yukawa-type tensor potential are obtained for an arbitrary spin-orbit coupling quantum number κ. We deduce the energy eigenvalue equations and corresponding upper- and lower-spinor wave functions in both the pseudospin and spin symmetry cases. Numerical results of the energy eigenvalue equations and the upper- and lower-spinor wave functions are presented to show the effects of the external potential and particle mass parameters as well as pseudospin and spin symmetric constants on the bound-state energies and wave functions in the absence and presence of the tensor interaction.     

相对论谐振子下的自旋和赝自旋轨道伙伴态劈裂

通过求解具有谐振子势的径向标量势与矢量势的Dirac方程, 分别分析了原子核中赝自旋和自旋双重态的能级劈裂和波函数劈裂随着谐振子的振动频率参数ω和描述谐振子势阱底偏离中心参数r₀的变化关系. 研究发现, 这些参数对于赝自旋和自旋双重态的能级劈裂和波函数劈裂都有着显著的影响. 此外, 也研究了能级劈裂和波函数劈裂随着量子数的变化关系. 由于参数ω与核子数有关, 而参数r₀与形变核有关, 所以以这些参数为变量对于赝自旋劈裂和自旋劈裂的研究是有意义的, 研究的结果至少可以定性地应用到大部分原子核中.     

Pseudospin quantum computation in semiconductor nanostructures

We theoretically show that spontaneously interlayer-coherent bilayer quantum Hall droplets should allow robust and fault-tolerant pseudospin quantum computation in semiconductor nanostructures with voltage-tuned external gates providing qubit control and a quantum Ising Hamiltonian providing qubit entanglement. Using a spin-boson model, we estimate decoherence to be small (approximately 10(-5)).     

Exact Spin and Pseudospin Symmetry Solutions of the Dirac Equation for Mie-Type Potential Including a Coulomb-like Tensor Potential

We solve the Dirac equation for Mie-type potential including a Coulomb-like tensor potential under spin and pseudospin symmetry limits with arbitrary spin–orbit coupling quantum number κ. The Nikiforov–Uvarov method is used to obtain analytical solutions of the Dirac equation. Since it is only the wave functions which are obtained in a closed exact form; as for the eigenvalues, only the eigenvalue equations have been given and they have been solved numerically. It is also shown that the degeneracy between spin doublets and pseudospin doublets is removed by tensor interaction.     

Oscillations of the Degree of Circular Polarization in the Optical Spin Hall Effect

The optical spin Hall effect appears when elastically scattered exciton polaritons couple to an effective magnetic field inside of quantum wells in semiconductor microcavities. Theory predicts an oscillation of the pseudospin of the exciton polaritons in time. Here, we present a detailed analysis of momentum space dynamics of the exciton polariton pseudospin. Compared to what is predicted by theory, we find a higher modulation of the temporal oscillations of the pseudospin. We attribute the higher modulation to additional components of the effective magnetic field which have been neglected in the foundational theory of the optical spin Hall effect. Adjusting the model by adding non-linear polariton-polariton interactions, we find a good agreement in between the experimental results and simulations.     

Effective pseudospin wave model for the coherent stripe phase in a bilayer system

Hartree–Fock theory predicts a stripe-like ground state for the two-dimensional electron gas in a bilayer quantum Hall system in a quantizing magnetic field at filling factor 4N+1 (with N>0). This stripe state contains quasi-1D linear coherent regions where electrons are delocalized across both wells and which support low-energy collective excitations in the form of phonons and pseudospin waves. We have recently computed the dispersion relation of these low-energy modes in the generalized random phase approximation. In this work, we propose an effective pseudospin model in which the stripe state is modeled as an array of coupled 1D anisotropic X–Y systems. The coupling constants and stiffness of our model are extracted from the density and pseudospin response functions computed in the GRPA.     

Approximate any 1-state solutions of the Dirac equation for modified deformed Hylleraas potential by using the Nikiforov-Uvarov method

<正>We investigate the spin and pseudospin symmetries of the Dirac equation under modified deformed Hylleraas potential via a Pekeris approximation and the Nikiforov-Uvarov technique.A tensor interaction of Coulomb form is considered and its degeneracy-removing role is discussed in detail.The solutions are reported for an arbitrary quantum number in a compact form and useful numerical data are included.     

Quantum phase transitions in bilayer quantum hall systems at a total filling factor nuT=1

We construct a quantum Ginsburg-Landau theory to study the quantum phase transition from the excitonic superfluid to a possible pseudospin density wave (PSDW) at some intermediate distances driven by the magnetoroton minimum collapsing at a finite wave vector. We explicitly show that the PSDW takes a square lattice structure. We suggest the existence of zero-point quantum fluctuation generated vacancies in the PSDW and that correlated hopping of vacancies in the active and passive layers in the PSDW state leads to very large and temperature dependent drag consistent with the experimental data. Comparisons with previous numerical calculations are made. Further experimental implications are given.     

Chemisorption on a quantum dot

The quantum kinetic equations for a “quantum dot-adatom” system are derived. It is demonstrated that the inclusion of the interaction between a quantum dot and an adatom leads to an increase in the quantum dot radius. The perturbations of the electron density of the quantum dot and the adatom upon chemisorption are calculated.     

Pseudospin and spin symmetry in the Dirac equation with Woods-Saxon potential and tensor potential

The Dirac equation is solved approximately for the Woods-Saxon potential and a tensor potential with the arbitrary spin-orbit coupling quantum number k \kappa under pseudospin and spin symmetry. The energy eigenvalues and the Dirac spinors are obtained in terms of hypergeometric functions. The energy eigenvalues are calculated numerically.     

量子点双链中电子自旋极化输运性质

利用非平衡格林函数方法, 研究了与单个量子点耦合的量子点双链中电子自旋极化输运性质. 由于系统中Rashba自旋轨道耦合产生的自旋相关的相位, 电子通过上下两种路径时, 自旋不同的电子干涉情况不同, 从而导致了电极中的自旋极化流. 左右两电极间的偏压使单个量子点中的自旋积聚在很大能量区域内能够保持较大的值. 由于系统结构的左右不对称, 正负偏压下自旋积聚情况完全不同. 这些计算结果将有助于实验上设计新型的自旋电子学器件.     

Quantum Dot Research: Current State and Future Prospects

This article reviews the current state of research involving semiconductor quantum dots, provides a brief review of the theory behind their unique properties, and an introduction explaining the importance of quantum dot research. The characteristic shifting of the band gap energy with quantum dot size, as predicted from the density of states for low-dimensional structures, allows experimental measurements to determine the extent to which quantum confinement effects play a role in the resulting properties. A few of the current techniques used to measure the presence and physical characteristics of quantum dots and their energy levels is reviewed, including transmission electron microscopy, optical transmission, and Raman and photoluminescence spectroscopy. Finally, some of the more exciting applications for quantum dots currently being researched for use in the field of optoelectronics are reviewed, including quantum dot infrared photodetectors, quantum dot lasers, and quantum dot solar cells. Comments are made on the current progress and the future prospects of quantum dot research and device applications.     

Bound-state solutions of the Dirac-Rosen-Morse potential with spin and pseudospin symmetry<Superscript>⋆</Superscript>

The energy spectra and the corresponding two-component spinor wave functions of the Dirac equation for the Rosen-Morse potential with spin and pseudospin symmetry are obtained. The s -wave ( k \kappa = 0 state) solutions for this problem are obtained by using the basic concept of the supersymmetric quantum mechanics approach and function analysis (standard approach) in the calculations. Under the spin symmetry and pseudospin symmetry, the energy equation and the corresponding two-component spinor wave functions for this potential and other special types of this potential are obtained. The extension of this result to the k \kappa 1 \neq 0 state is suggested.