Electronic structure and binding energy of a hydrogenic impurity in a hierarchically self-assembled GaAs/AlxGa1-xAs quantum dot

We calculate the electronic structures and binding energy of a hydrogenic impurity in a hierarchically self-assembled GaAs/AlxGa1-xAs quantum dot (QD) in the framework of effective-mass envelope-function theory. The variation of the electronic structures and binding energy with the QD structure parameters and the position of the impurity are studied in detail. We find that (1) acceptor impurity energy levels depend more sensitively on the size of the QD than those of a donor impurity; (2) all impurity energy levels strongly depend on the GaAs quantum well (QW) width; (3) a donor impurity in the QD has only one binding energy level except when the GaAs QW is large; (4) an acceptor impurity in the QD has two binding energy levels, which correspond to heavy- and light-hole quantum states; (5) the binding energy has a maximum value when the impurity is located below the symmetry axis along the growth direction; and (6) the binding energy has a minimum value when the impurity is located at the top corner of the QD. (c) 2006 American Institute of Physics.

Degree of fourth-order coherence by double Hanbury Brown-Twiss detections

Photon quantum statistics of light can be shown by the high-order coherence. The fourth-order coherences of various quantum states including Pock states, coherent states, thermal states and squeezed vacuum states are investigated based on a double Banbury Brown Twiss (HBT) scheme. The analytical results are obtained by taking the overall efficiency and background into account.

Method for measuring two-qubit entanglement of formation by local operations and classical communication

We present a parametrically efficient method for measuring the entanglement of formation E-f in an arbitrarily given unknown two-qubit state rho(AB) by local operations and classical communication. The two observers, Alice and Bob, first perform some local operations on their composite systems separately, by which the desired global quantum states can be prepared. Then they estimate seven functions via two modified local quantum networks supplemented a classical communication. After obtaining these functions, Alice and Bob can determine the concurrence C and the entanglement of formation E-f.

Quantum interference effects of two coherent population trapping states on the atomic spectral lines of a F-e=0 -> F-g=1 transition

We investigate the fluorescence spectrum in a nearly degenerate atomic system of a F-e = 0 -> F-g = 1 transition by analytically solving Schrodinger equations. An ultranarrow fluorescence spectral line in between the two coherent population trapping windows has been found. Our analytic solutions clearly show the origin of the ultranarrow spectral line. Due to quantum interference effects between two coherent population trapping states, the width and intensity of the central spectral line can be controlled by an external magnetic field. Such an effect may be used to detect a magnetic field.

Tuning of the two electron states in quantum rings through the spin-orbit interaction

The effect of the Coulomb interaction on the energy spectrum and anisotropic distribution of two electron states in a quantum ring in the presence of Rashba spin-orbit interaction (RSOI) and Dresselhaus SOI (DSOI) is investigated in the presence of a perpendicular magnetic field. We find that the interplay between the RSOI and DSOI makes the single quantum ring behaves like a laterally coupled quantum dot and the interdot coupling can be tuned by changing the strengths of the SOIs. The interplay can lead to singlet-triplet state mixing and anticrossing behavior when the singlet and triplet states meet with increasing magnetic field. The two electron ground state displays a bar-bell-like spatial anisotropic distribution in a quantum ring at a specific crystallographic direction, i.e., [110] or [1 (1) over bar0], which can be switched by reversing the direction of the perpendicular electric field. The ground state exhibits a singlet-triplet state transition with increasing magnetic field and strengths of RSOI and DSOI. An anisotropic electron distribution is predicted which can be detected through the measurement of its optical properties.

Magnetic quantum oscillations for the surface states of topological insulator Bi2Se3

We study quantum oscillations of the magnetization in Bi2Se3 (111) surface system in the presence of a perpendicular magnetic field. The combined spin-chiral Dirac cone and Landau quantization produce profound effects on the magnetization properties that are fundamentally different from those in the conventional semiconductor two-dimensional electron gas. In particular, we show that the oscillating center in the magnetization chooses to pick up positive or negative values depending on whether the zero-mode Landau level is occupied or empty. An intuitive analysis of these features is given and the subsequent effects on the magnetic susceptibility and Hall conductance are also discussed.

Spin states in semiconductor quantum dot with a single magnetic ion

We investigate theoretically CdTe quantum dots containing a single Mn2+ impurity, including the sp-d exchange interaction between carriers and the magnetic ion and the short-range exchange interaction between electron and hole. We find anticrossing behaviors in the energy spectrum of the electron-hole (e-h) pair that arise from the interplay between exchange interactions and the magnetic field. In addition to the s-d exchange interaction, we find that other mechanisms inducing the anticrossings become important in the strong heavy hole-light hole (hh-lh) mixing regime. The transition strengths between the states with spin projection of Mn2+ ion S-z not equal -5/2 (S-z = -5/2) decrease (increase) with increasing magnetic fields due to the alignment of the Mn2+ spin. The spin splitting of the e-h pair states depends sensitively on the external magnetic and electric field, which reveals useful information about the spin orientation and position of the magnetic ion. Meanwhile, the manipulation of the position of the magnetic ion offers us a way to control the spin splitting of the carriers. (C) 2008 Elsevier B.V. All rights reserved.

Electronic states of InAs/GaAs tyre-shape quantum ring

In the framework of the effective mass theory, this paper calculates the electron energy levels of an InAs/GaAs tyre-shape quantum ring (TSQR) by using the plane wave basis. The results show that the electron energy levels are sensitively dependent on the TSQR's section thickness d, and insensitively dependent on TSQR's section inner radius R-1 and TSQR's inner radius R-2. The model and results provide useful information for the design and fabrication of InAs/GaAs TSQRs.

Spin states and persistent currents in a quantum ring with an embedded magnetic impurity

Spin states and persistent currents are investigated theoretically in a quantum ring with an embedded magnetic ion under a uniform magnetic field including the spin-orbit interactions. The magnetic impurity acts as a spin-dependent delta-potential for electrons and results in gaps in the energy spectrum, consequently suppressing the oscillation of the persistent currents. The competition between the Zeeman splittings and the s-d exchange interaction leads to a transition of the electron ground state in the ring. The interplay between the periodic potential induced by the Rashba and Dresselhaus spin-orbit interactions and the delta-potential induced by the magnetic impurity leads to significant variation in the energy spectrum, charge density distribution, and persistent currents of electrons in the ring.

Spin states in InAs/AlSb/GaSb semiconductor quantum wells

We investigate theoretically the spin states in InAs/AlSb/GaSb broken-gap quantum wells by solving the Kane model and the Poisson equation self-consistently. The spin states in InAs/AlSb/GaSb quantum wells are quite different from those obtained by the single-band Rashba model due to the electron-hole hybridization. The Rashba spin splitting of the lowest conduction subband shows an oscillating behavior. The D'yakonov-Perel' spin-relaxation time shows several peaks with increasing the Fermi wave vector. By inserting an AlSb barrier between the InAs and GaSb layers, the hybridization can be greatly reduced. Consequently, the spin orientation, the spin splitting, and the D'yakonov-Perel' spin-relaxation time can be tuned significantly by changing the thickness of the AlSb barrier.

Magneto - Transport of electron symmetric and antisymmrtric states in highly doped InGaAs/InAlAs single quantum well

Beating patterns in longitudinal resistance caused by the symmetric and antisymmetric states were observed in a heavily doped InGaAs/InAlAs quantum well by using variable temperature Hall measurement. The energy gap of symmetric and antisymmetric states is estimated to be 4meV from the analysis of beating node positions. In addition, the temperature dependences of the subband electron mobility and concentration were also studied from the mobility spectrum and multicarrier fitting procedure.

Electron and hole states in diluted magnetic semiconductor quantum dots

The electronic structure of a diluted magnetic semiconductor (DMS) quantum dot (QD) is studied within the framework of the effective-mass theory. We find that the energies of the electron with different spin orientation exhibit different behavior as a function of magnetic field at small magnetic fields. The energies of the hole decreases rapidly at low magnetic fields and saturate at higher magnetic field due to the sp-d exchange interaction between the carriers and the magnetic ions. The mixing effect of the hole states in the DMS QD can be tuned by changing the external magnetic field. An interesting crossing behavior of the hole ground state between the heavy-hole state and the light-hole state is found with variation of the QD radius. The strength of the interband optical transition for different circular polarization exhibts quite different behavior with increasing magnetic field and QD radius.

Observation of intershell and hybridized energy states in InAs/GaAs quantum dots

We have investigated the evolution of exciton state filling as a function of excitation power density in InAs/GaAs quantum dots (QDs). In addition to the emission bands of exciton recombination corresponding to the atom-like S, P, and D, etc. shells of quantum dots, it was observed that some extra states, P-' (between the S and P shells) and D-' (between the P and D shells), appear in the spectra with increasing number of excitons occupying the QDs. The emergence of these intershell excitonic levels is an experimental demonstration of strong exciton-exciton exchange interaction and coupling as well as state mixing and hybridization of a multiexciton system in quantum dots.

Exciton states of vertically stacked self-assembled InAs quantum disks in an axial magnetic field

We have studied the exciton states of vertically stacked self-assembled quantum disks within the effective mass approximation. The ground energies of a heavy-hole and a light-hole excitons as functions of the vertical disk separation are presented and discussed. The transition energy of a heavy-hole ground-state exciton is calculated and compared with the experimental data. The binding energies are discussed in terms of the probability of ground wave function. The ground energies of a heavy-hole and a light-hole excitons as functions of the applied axial magnetic field are calculated and the effect of disk size (radius of disks) on exciton energies is discussed. (c) 2006 Elsevier B.V. All rights reserved.

Electronic states in InAs quantum spheres and ellipsoids

The eight-band effective-mass Hamiltonian of the free-standing narrow-gap InAs quantum ellipsoids is developed, and the electron and hole electronic structures as well as optical properties are calculated by using the model. The energies, wave functions and transition probabilities of quantum spheres as functions of the radius of quantum sphere R is presented. It is found that the energy levels do not vary as 1/R-2, which is caused by the coupling between the conduction and valence bands, and by the constant terms correspond to the spin-orbit splitting energy. The blueshifts of hole states depend strongly on the coupling from electron states, so that the order of hole states changes as has been predicted in experiment. The exciton binding energies are calculated, the calculated excitonic gaps as functions of the ground exciton transition energy are in good agreement with the photoluminescence measured spectra in details. Finally, the hole energy levels and the linear polarization factors in InAs quantum ellipsoids as functions of the aspect ratio are presented. The state 1S(Z up arrow)((1/2)) becomes the hole ground state when e is larger than 2.4. The saturation value of the linear polarization factors of the InAs long ellipsoids of diameter 2.0 nm is 0.86, in agreement with the experimental results.