Electromagnetically induced transparency due to intervalence band coherence in a GaAs quantum well

We demonstrate electromagnetically induced transparency in the transient optical response in a GaAs quantum well by using the nonradiative coherence between the heavy-hole and the light-hole valence bands.     

Photon avalanche in a doped quantum well

The possibility of a photon avalanche in a doped quantum well irradiated by IR light is predicted. The proposed model includes the three lowest size-quantization subbands. The exciting IR light frequency is assumed to be in resonance with the transition between the second and third subbands. Probabilities of the Auger transitions responsible for the avalanche-like multiplication of electrons in excited states are calculated for the above-threshold light intensities (j>j _th). By numerically solving the rate equations for electron populations in the three subbands, it is shown that the values j _th in quantum wells with the free-carrier densities n ₀～10¹² cm^?2 are of the order of hundreds of kilowatt per square centimeter and do not depend on the rates of phototransition between the first and second subbands. Characteristic times of establishing the quasi-equilibrium distributions of electrons over the subbands lie in the picosecond range and steeply increase at near-threshold intensities.     

Laser-induced quantum coherence in a semiconductor quantum well

The phenomenon of electromagnetically induced quantum coherence is demonstrated between three confined electron subband levels in a quantum well which are almost equally spaced in energy. Applying a strong coupling field, two-photon resonant with the 1-3 intersubband transition, produces a pronounced narrow transparency feature in the 1-2 absorption line. This result can be understood in terms of all three states being simultaneously driven into "phase-locked" quantum coherence by a single coupling field. We describe the effect theoretically with a density matrix method and an adapted linear response theory.     

Parameter-dependent photon echo induced in CdSe/ZnS quantum dot quantum well

The two pulse photon echo (2PPE) phenomena induced by the 1s-1s electronic transition in CdSe/ZnS quantum dot quantum well (QDQW) has been studied by employing semiconductor Bloch equations. The energy eigenvalues and eigenfunctions of electrons and holes have been obtained by solving the stationary Schrödinger equation under effective-mass approximation. The Coulomb interaction, which changes with the size variation of QDQW, has been calculated and analyzed as a perturbation. The variations of the electric transition dipole moment and the energy interval with the changing of the size and structure of the QDQW have also been obtained. It has been shown from the numerical calculation results that the efficiency of 2PPE can be controlled by the variation of the size and structure of the QDQW and the mechanism has been explained in terms of the quantum size confined effect (QSCE) theory.     

Coherent Zeeman resonance from electron spin coherence in a mixed-type GaAs/AlAs quantum well

Coherent Zeeman resonance from electron spin coherence is demonstrated in a Lambda-type three-level system, coupling electron spin states via trions. The optical control of electron density that is characteristic of a mixed-type quantum-well facilitates the study of trion formation as well as the effects of many-body interactions on the manifestation of electron spin coherence in the nonlinear optical response.     

Photon echo excited in multilevel quantum media by ultimately short pulses

The photon echo excitated in a multilevel quantum medium by two or more ultimately short pulses with duration down to one period of optical oscillations is studied theoretically. It is shown that the number of echo responses formed in the system depends on the number of quantum levels covered by the spectrum of the exciting pulses and strongly increases with this number. General equations for the spatio-temporal characteristics of the multipulse echo signals are obtained.     

非对称半导体量子阱中自发辐射相干诱导透明

研究了一束低强度探测脉冲光场在一个非对称半导体量子阱中的传输特性.在相同参数条件下,通过由自发辐射相干产生的交叉耦合系数来调控介质对探测场吸收、色散的变化规律.结果表明:从自发辐射相干的引入到达到相干最大,介质的吸收不断减小,同时强色散也随之进入透明窗口.     

Slow light propagation via quantum coherence in a semiconductor quantum well

With the Schrödinger equations, we investigate the low-intensity light pulse propagation through a semiconductor quantum wells. Through studying the dispersion and absorption properties of the weak probe field, it is shown that slow light propagation is observed in this system. From the view point of practical purpose, it is more advantageous than its corresponding atomic system. Such investigation of slow light propagation may lead to important practical applications in semiconductor quantum information.     

GaAs quantum well structures investigation by local cathodoluminescence

The article shows the cathodoluminescence technique application to a quality analysis of a semiconductor multilayer heterostructures. Two structures with a GaAs quantum well embedded between the AlGaAs and GaInP barriers were investigated. The AlGaAs/GaAs/GaInP and GaInP/GaAs/AlGaAs structures were grown by MOCVD on a GaAs substrate. In this work we study the interface quality of quantum-dimensional GaAs layer by means of the local cathodoluminescence. Degradation and broadening of GaAs/GaInP interface occurring during the growth process of GaAs on GaInP layer was assumed to result in the formation of a layer with mixed composition at the interface. In addition, the presence of the layer prevented the formation of a quantum well in the GaAs layer. The transition layer was clearly observed by the cathodoluminescence. In the other case it was found that the growth of a structure with GaAs layer on top of AlGaAs produced a quantum well with a 10 nm thickness. The interface quality and layer thicknesses were also confirmed by the X-ray diffraction investigation of these structures.     

Laser field induced interband absorption in a strained GaAs/GaAlAs double quantum well system

Effect of laser field intensity on exciton binding energies is investigated in a GaAs/ GaAlAs double quantum well system. Calculations have been carried out with the variational technique within the single band effective mass approximations using a two parametric trial wave function. The interband emission energy as a function of well width is calculated in the influence of laser field. The laser field induced photoionization cross-section for the exciton placed at the centre of the quantum well is computed as a function of normalized photon energy. The dependence of the photoionization cross-section on photon energy is carried out for the excitons. The resulting spectra are brought out for light polarized along and perpendicular to the growth direction. The intense laser field dependence of interband absorption coefficient is investigated. The results show that the exciton binding energy, interband emission energy, the photoionization cross-section and the interband absorption coefficient depend strongly on the well width and the laser field intensity. Our results are compared with the other existing literature available.     

Directional quantum random walk induced by coherence

Quantum walk (QW), which is considered as the quantum counterpart of the classical random walk (CRW), is actually the quantum extension of CRW from the single-coin interpretation. The sequential unitary evolution engenders correlation between different steps in QW and leads to a non-binomial position distribution. In this paper, we propose an alternative quantum extension of CRW from the ensemble interpretation, named quantum random walk (QRW), where the walker has many unrelated coins, modeled as two-level systems, initially prepared in the same state. We calculate the walker's position distribution in QRW for different initial coin states with the coin operator chosen as Hadamard matrix. In one-dimensional case, the walker's position is the asymmetric binomial distribution. We further demonstrate that in QRW, coherence leads the walker to perform directional movement. For an initially decoherenced coin state, the walker's position distribution is exactly the same as that of CRW. Moreover, we study QRW in 2D lattice, where the coherence plays a more diversified role in the walker's position distribution.     

Potentials induced by the electron-optical-phonon interaction in a quantum well

The potential induced by the electron-optical-phonon interaction in a quantum well (QW) is investigated by means of the perturbation theory. We consider the interactions of an electron with both bulklike confined longitudinal optical (LO) phonons and four branches of interface optical (IO) phonons. The spatial distributionV _i(z) of the induced potential for QW structures with different heterolayer compositions and different well widths is calculated in detail. The numerical results show that the heterolayer composition of the QW plays an important role in determining the shape ofV _i(z) and that the existence of IO-phonons is important to the electronic states in QWs.     

High-strain InGaAs/GaAs quantum well grown by MOCVD

High-strain InGaAs/GaAs quantum wells （QWs） are grown by low-pressure metal-organic chemical vapor deposition （LP-MOCVD）. Photoluminescence （PL） at room temperature is applied for evaluation of the optical property. The influence of growth temperature, V/III ratio, and growth rate on PL characteristic are investigated. It is found that the growth temperature and V/III ratio have strong effects on the peak wavelength and PL intensity. The full-width at half-maximum （FWHM） of PL peak increases with higher growth rate of InGaAs layer. The FWHM of the PL peak located at 1039 nm is 20.1 meV, which grows at 600 ℃ with V/ III ratio of 42.7 and growth rate of 0.96 μm/h.     

Potentials induced by the electron-optical-phonon interaction in a quantum well

The potential induced by the electron-optical-phonon interaction in a quantum well (QW) is investigated by means of the perturbation theory. We consider the interactions of an electron with both bulklike confined longitudinal optical (LO) phonons and four branches of interface optical (IO) phonons. The spatial distributionV _i(z) of the induced potential for QW structures with different heterolayer compositions and different well widths is calculated in detail. The numerical results show that the heterolayer composition of the QW plays an important role in determining the shape ofV _i(z) and that the existence of IO-phonons is important to the electronic states in QWs.     

Spin-Hall effect in a [110] GaAs quantum well

A self-consistent treatment of the spin-Hall effect requires consideration of the spin-orbit coupling and electron-impurity scattering on equal footing. This is done here for the experimentally relevant case of a [110] GaAs quantum well [Sih, Nature Phys. 1, 31 (2005)]. Working within the framework of the exact linear response formalism we calculate the spin-Hall conductivity including the Dresselhaus linear and cubic terms in the band structure, as well as the electron-impurity scattering and electron-electron interaction to all orders. We show that the spin-Hall conductivity naturally separates into two contributions, skew-scattering and side-jump, and we propose an experiment to distinguish between them.