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The theory of the photocurrent through the photodetector based on a two-level semiconductor quantum dot (QD) is presented. The analytical expressions of the matrix elements of the electronic transitions generated by the absorption of the circularly polarized photons are derived in the lowest order of the perturbation theory with respect to the electron tunneling interaction as well as the electron-photon interaction. From these expressions the mechanism of the generation of the spin-polarized of electrons in the photocurrent is evident. It follows that the photodetector based on the two-level semiconductor QD can be used as the model of a source of highly spinpolarized electrons.

The linear and nonlinear optical absorption via one and two-photon processes in the finite symmetric parabolic quantum well (FSPQW) under the applied magnetic field have been studied numerically for typical GaAs/Ga x Al 1− x As. The analytical expression of the magneto-optical absorption coefficient (MOAC) is obtained by relating it to the transition probability for the absorption of photons. The effects of the magnetic field, the temperature, and the well width on MOAC and full-width at half-maximum (FWHM) are investigated. Results reveal that MOAC and FWHM are monotonic functions of these factors in both one and two-photon absorption processes. Obtained results also show that the magneto-optical properties of FSPQW can be controlled by changing these parameters. This suggests a new capacity for magneto-optical device applications.

We have fabricated the finite-sized amorphous ${\rm Mo}_{80}{\rm Ge}_{20}$ superconducting networks with 10 $\,\times\,$ 10 square holes and directly observed the vortex structures by means of using the scanning SQUID microscope. On the increase of the field in a stepwise manner, the vortex penetration into the network is likely to follow the Bean critical model, wherein vortices first enter the network from the edges and penetrate deeper toward the center of the network as the field increases. We observed that the evolution of vorticity mainly occurred along the diagonal direction of the network, which has a narrow wire compared with the hole size. The vortex pattern was strongly modified as the system was cooled down below $T_{c}$ . A diagonal vortex array appeared at intermediate temperatures, and is transformed into the isolated vortices at lower temperatures due to the strong repulsive interaction between vortices.

The quantum acoustoelectric (QAE) current is studied theoretically in a doped superlattice (DSL). The physical problem is investigated in the region ql ≫ 1 (where q is the acoustic wave number and l is the electrons mean free path). We obtain analytical expression for the QAE current in the DSL by using the quantum kinetic equation for electron-external acoustic wave interaction and electron-acoustic phonon (internal acoustic wave) scattering. A nonlinear dependence of the QAE current on the frequency of external acoustic wave ω q → , the temperature T of the system and the characteristic parameters of DSL is achieved. The computational results for a specific GaAs:Si/GaAs:Be DSL indicates that the existent peaks in the DSL may be due to the transition between mini-bands n → n′. All these results are compared with those for normal bulk semiconductors to show the differences. Finally, the quantum theory of the QAE current in the DSL is newly developed.

An analytic expression for the acoustoelectric current (AC) j ac induced by electron-external acoustic wave interactions and electron-internal acoustic wave (internal phonons) scattering in a quantum well (QW) is calculated by using the quantum kinetic equation for electrons. The physical problem is investigated in the region ql ≫ 1 (where q is the acoustic wave number and l is the electrons mean free path). The dependence of the AC j ac on the external acoustic wave frequency $$\omega _{\vec q}$$ , the width of the QW L and the temperature T for a specific QW of AlGaAs/GaAs/AlGaAs is achieved by using a numerical method. The computational results show that the dependence of the AC j ac on the temperature T, the external acoustic wave frequency $$\omega _{\vec q}$$ , the width of the QW L is non-monotonic and that the peaks can be attributed to transitions between mini-bands n → n′. The dependence of the AC j ac on the temperature T and the Fermi energy ∈ F is obtained, and a maximum of the AC j ac for ∈ F = 0.038 eV and $$\omega _{\vec q} = 3 \times 10^{11} s^{ - 1}$$ seen at T = 50 K, which agrees with the experimental results for AlGaAs/GaAs/AlGaAs QWs. All these results are compared with those for normal bulk semiconductors and superlattices to show the differences. Finally, the quantum theory of the acoustoelectric effect in a quantum well is newly developed.

The acoustomagnetoelectric (AME) field in a quantum well with a parabolic potential (QWPP) has been studied in the presence of an external magnetic field. The analytic expression for the AME field in the QWPP is obtained by using the quantum kinetic equation for the distribution function of electrons interacting with external phonons. The dependence of the AME field on the temperature T of the system, the wavenumber q of the acoustic wave and external magnetic field B for the specific AlAs/GaAs/AlAs is achieved by using a numerical method. The problem is considered for both cases: The weak magnetic field region and the quantized magnetic field region. The results are compared with those for normal bulk semiconductor and superlattices to show the differences, and we use the quantum theory to calculate the AME field in the QWPP.

numerical calculation methods. In this report, we present a derivation of the analytical forms of the resonance terms in the expression of the two-point Green’s function. For that purpose, the system of Dyson equations for the two-point nonequilibrium Green’s functions in the complex-time Keldysh formalism was established to the second order in the tunneling coupling constants with the mean field approximation for the statistical averages of the products of four electron creation and destruction operators. This system of Dyson equations was solved exactly by means of the computer algebra and the analytical expressions for the resonance terms are derived. The conditions for the existence of the Kondo or the Fano resonances were found.

Theoretical Description of the Manipulation of a Double Quantum Dot as a Charge Qubit Nguyen Van Hieu and Nguyen Bich Ha Institute of Materials Science, Vietnamese Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam (Received 12 December 2007) The charge qubit operation on an isolated double quantum dot, i.e., the manipulation of electron charge distribution and charge current in an isolated double quantum dot by changing the bias voltage applied to the gates of two quantum dots was performed in recent experimental works towards the use of this charge qubit in quantum information processing. In this work, we present the theory of charge qubit operation of this kind on an isolated double quantum dot consisting of two single-level quantum dots connected one with another by means of electron tunneling through a potential barrier and containing only one electron. The system of rate equations for matrix elements of density matrix of electron system was derived. The formulae determining the time dependence of the charge distribution in the double quantum dot due to abrupt changes in the bias voltage applied to the gates of two quantum dots during the manipulation process were established. The comparison with experimental data was carried out for the special case of decoherence due to the interaction of electron with environment. PACS numbers: 73.21.La, 73.23.Hk, 73.63.Kv

We use the Logunov–Tavkhelidze quasipotential approach to study some processes of quantum chromodynamics at finite densities and temperatures. The dynamic equation for the color superconductivity is derived. We discuss the spontaneous breaking of the chiral, flavor, and color symmetries and also the possibility of constructing a field theory of the composite three-quark systems.

The theory of the quantum information transmission between two semiconductor two-level quantum dots as two qubits through an intermediary photon gas in a cavity is presented. The reduced density matrix of each two-level quantum dot is the quantum information encoded into this qubit. The quantum information exchange between two distant qubits imbedded in the photon gas is performed in the form of the mutual dependence of their reduced density matrices due to the interaction between the electrons in the qubits and the photon gas. The system of rate equations for the reduced density matrix of the two-qubit system is derived. From the solution of this system of equations it follows the mutual dependence of the reduced density matrices of two distant qubits.

The explicit expressions for the imaginary time normal and anomalous two-point Green functions of the strongly correlated itinerant electron (or hole) system with the quantum antiferromagnetic and ferromagnetic couplings and the strong Coulomb repulsion, as well as those of the real time ones at a finite temperature, are derived in the mean field approximation. In the limit of the infinitely strong on-site Coulomb repulsion, the system becomes that with the single occupation constraint.

The quantum theory of the anyon gas was developed in the framework of the field theoretical formalism. The existence of the classical background CS gauge field created by the quasiparticles below the Fermi level and acting as some effective magnetic field was taken into account. The expressions of the two-point Green functions of the free and interacting CS gauge fields were derived. It was shown that they determine the conductivity tensor of the anyon gas. The relevance to the FQHE was discussed.

It was shown that in a free anyon gas there exists a composite vector gauge field with the effective action containing a Chern-Simons term. The momentum dependence of the energy of the composite boson was found. The mixing between Chern-Simons boson and photon gives rise to the appearance of new quasiparticles -Chern-Simons polaritons. The dispersion equations of Chern-Simons polaritons were derived.

The equation in the ladder approximation was derived for the two-particle Green function of the itinerant electrons with the Heisenberg ferromagnetic and antiferromagnetic interaction. The general form of its solution was found. The existence of the pole in this solution is related to the condensation of the bound pairs in the corresponding spin state. The condition for the pole determines the critical temperature T c . The effective interaction between the mobile holes due to the mobile hole-localized spin coupling in the two-band Hubbard model was also studied.

Conventional metamaterial absorbers, which consist of a dielectric spacer sandwiched between metamaterial resonators and a metallic ground plane, have been inherently anisotropic. In this paper, we present an alternative approach for isotropic perfect absorbers using symmetric metamaterial structures. We show that by systematically manipulating the electrically and magnetically induced losses, one can achieve a desired absorption without breaking the structural homogeneity. Finite integration simulations and standard retrieval method are performed to elaborate on our idea.

Path — integral formulation of quantum mechanics has been proposed long ago by Feynman (Feynman and Hibbs, 1965) and was then widely applied in quantum physics. Nowadays an unified theory based on the use of the functional integrals was firmly established and developed for studying all quantum systems, including many — body systems in statistical physics and condensed matter theory (Sakita, 1985; Wiegel, 1986; de Wit, 1981) as well as those of interacting quantized fields (Fadeev, 1976; Itzykson and Zuber, 1980; Lee, 1976; Ramond, 1981). This review is an introduction to the functional integral techniques in statistical physics and condensed matter theory. It is written for the readers who had no experience to work with the functional integrals. Therefore together with the elementary proof of the basic formulae of the functional integral techniques we explain the meaning of the functional integrals and show how can they be expressed in terms of the conventional integrals. We suppose that the readers had some basic understandings of the traditional methods of the quantum field theory in statistical physics (Abrikosov et al., 1965). The basic formulae of the functional integral techniques are derived in Sec. I for the bosonic systems and in Sec. II for the fermionic ones. They were applied widely in studying many problems of quantum theory of condensed matters. Some examples of these applications are presented in the concluding Sec. III.

We introduce a simple but general mechanism to realize the dual magnetic resonance exhibiting a broadband negative permeability. A satisfactory explanation, based on the second-order hybridization of symmetric metamaterials, for resonant splitting is given. It is manifested that the geometric correlation plays a vital role in controlling the hybridization strength. Transfer matrix simulations and equivalent circuit model analysis are performed to corroborate our idea.

The general theory of the time-resolved luminescence of the coupled system consisting of a single-mode microcavity and a two-level quantum dot containing one electron placed inside this microcavity is presented. It is based on the study of the time evolution of the density matrix of a larger system consisting of one electron in the two-level quantum dot, single-mode photons in the microcavity and external photons in a spatial region in which the emitted photons are detected. The decoherence of the system is taken into account in the Markov approximation. The explicit analytical form of the time dependence of the intensity of the emitted photon beam is established. It depends not only on the physical parameters of the system but also contains the matrix elements determining the initial condition of the luminescence process.

A physical model of the quantum information exchange between two qubits is studied theoretically. The qubits are two identical two-level atoms, the physical mechanism of the quantum information exchange is the mutual dependence of the reduced density matrices of two qubits generated by their couplings with a multimode radiation field. The Lehmberg-Agarwal master equation is exactly solved. The explicit form of the mutual dependence of two reduced density matrices is established. The application to study the entanglement of two qubits is discussed.

The superconducting pairing of fermions is studied in the framework of the functional intergral approach. The bi-local composite scalar and vector fields are introduced to describe the singlet and triplet pairings. The static (time-independent) fields are the superconducting order parameters. From the variational principle for the effective action of the composite fields we derive the generalised Ginzburg–Landau equations. They are also the extensions of the BCS gap equations.

We discuss quantum-mechanical many-body systems interacting with a topological field, known as topological quantum fields. Several topics on the theory of quantum fluids are examined. First we establish the existence of topological gauge fields in high-T c superconductors and in Heisenberg quantum antiferromagnets. Then we consider typical topological quantum fluids, known as quantum Hall fluids, which are systems exhibiting the fractional quantum Hall effect (FQHE). A theoretical model of these fluids is described in detail. We also discuss the long distance physics of topological quantum fluids, their topological order parameter and possible experimental tests of the theory.

It is shown that if the contribution of the holes in the lower valence bands Γ8 in CuCl is neglected, the state vectors of the stationary states of the excitons and hiexcitons in this semiconductor belong to irreducible representations of the rotation group, and their interaction is spherically symmetric. Due to this approximate symmetry, the partial wave expansion may be applied to the photon-photon scattering amplitude and the angular dependence of the cross-section of the resonant scattering via a definite biexciton state may be predicted. [Russian Text Ignored.]

A new version is presented for the microscopic theory of the resonant intensity dependence of the refractive index of a narrow gap zincblende semiconductor InSb. A general formula is derived to include the contributions from both the mechanisms: the free charge carrier plasma and the dynamical Burstein-Moss effect. The electron and hole distribution functions are determined by means of the transport equation. [Russian Text Ignored.]

The modulation of the dielectric susceptibility of direct band gap semiconductors due to the interaction with sound waves is considered up to second order of the deformation tensor. The role of the Coulomb interaction between electrons and the holes, i.e. that of exciton states with discrete and continuous energies, is taken into account. [Russian Text Ignored].

This report is a review of the authors papers on the RVB theory of high-T/sub c/ superconductivity. The authors represent only the main physical results; the details may be found in original articles. For the RVB system in a simple two-dimensional lattice they have the Hubbard Hamiltonian and in the case of the system with two inter-penetrating sublattices they assume the extended Hubbard Hamiltonian.

A microscopic theory is represented of the scattering of the excitonic polariton on the excitonic polariton in semiconductors with direct band gaps. All possible scattering mechanisms were taken into account. In the calculations the second quantization method was used in an effective manner. The general results were applied to the case of the single exciton level in CdS. The contributions from different scattering mechanisms were compared.

The transition is studied between a photon and “heavy” and “light” excitons in direct-band gap cubic semiconductors with a fourfold degenerated highest valence band at the center of the Brillouin zone. The transition matrix elements are calculated in the second-order approximation of the perturbation series with respect to a small constant proportional to the difference of the mass of the heavy and light holes. The algebraic equation determining the dispersion of the three-branch polaritons is derived. The spin structure of the wave functions of the corresponding excitons is established. [Russian Text Ignored].

A method is proposed for finding the auxiliary fields for all massless linear chiral representations of N-extended supersymmetry with arbitrary N. For each supermultiplet of free particles there exists a bilinear Lagrangian compatible with the supersymmetric rules of quantization and local with respect to the physical fields; the energy of systems of free fields is positive definite.

The reduction of the eleven-dimensional pure gravity theory to a field theory to a field theory in the four-dimensional Minkowski space-time by means of the spontaneous compactification of the extra dimensions is investigated. The contribution of the quantum fluctuations of the eleven-dimensional second rank symmetric tensor field to the curvatures of the space-time and the compactified space of the extra dimensions are calculated in the one-loop approximations. It is shown that there exist the values of the cosmological constant such that the resulting four-dimensional theory is self-consistent.

The interaction between the bosonic excitations as well as between the fermionic ones in the RVB systems with the (extended) Hubbard Hamiltonian were studied by means of the slave boson technique and the perturbation theory. The corresponding effective Hamiltonians have been found. It was shown, in particular, that in the RVB system with two interpenetrating sublattices there exists the effective attraction between two holons of different kinds as well as between two spinions of different kinds in the singlet state.

Perturbation is applied to study of the Wannier-Mott excitons in direct band gap cubic semiconductors with a fourfold degenerate highest valence band. The fine structure of exciton energy levels is investigated. General formulae are derived for the matrix elements of the perturbation. From these expressions it is straightforward to obtain values of the fine structure splittings of the energy levels and the wave functions of corresponding staes in any order of perturbation theory. A comparison with results of previous works is made.

The renormalization procedure of perturbation theory is applied to study polariton effects in the optical processes involving photons with energies near that of an exciton: resonant Raman scattering, resonant electronic Raman scattering, and resonant high — order optical harmonic generation. To demonstrate the general method and the computation technique we consider in this work a simple model with the following properties: (a) The semiconductor has a direct band gap with allowed electrical dipole transition and with nondegenerate valence and conduction bands. (b) We consider only the photons in a definite polarization state; they are in resonance with one bound state of an electron-hole pair, and we take into account only the transition between this exciton state and the photon in the given polarization state. We work in the framework of the Green's function approach and we shall see that this approach provides for the inclusion of damping effects in a relatively rigorous manner.

The role of polariton intermediate states in non-linear acousto-optical phenomena is studied. The matrix elements of the interaction processes acoustic phonon + photon photon + acoustic phonon, photon photon + 2 acoustic phonons are derived. The contribution of the effective photon–exciton transition is taken into account in any order. Then the exciton intermediate states are replaced by those of the corresponding polaritons. The damping is not neglected. [Russian Text Ignored].

The general properties of the damping constants of polaritons in the two-branch and three-branch models are considered in the framework of the Green's function method. In particular, the expressions for the damping constants of the polaritons in terms of those of the excitons are established. [Russian Text Ignored].

The Green functions of the electrons in the two-band Hubbard model with the strong on-site Coulomb repulsion were calculated by means of the perturbation theory with respect to the hopping term of the Hamiltonian. It was shown that in the slave boson technique we obtain the expressions different from the results of the calculations involving directly electron operators without using slave bosons. The physical meaning of this discrepancy was discussed.

The realization of irreducible representations of the SU(6) × SU(6) current algebra in the linear spaces of asymptotic creation and annihilation operators of particles at rest is studied. This approach is free of difficulties encountered when realizing this algebra in the Hilbert space of state vectors. A possibility of the classification of hadrons according to the irreducible representations of this algebra is considered.

In this paper mesons of spin and parity 2+, 1+, 0+ in SU(6) theory and its relativistic generalizations are considered. The connection between the representations 225 and 441 of the group U(6) and the representations 4212+ and 5940+ is explained with the aid of the scheme GL(6). It is shown that meson resonances A2, KII and f0 may belong to the representation 4212+ as well as to 5940+. Explicit expressions are given for the decay widths of all 2+ mesons and the matrix elements for 1+ and 0+ mesons with particular values of isospin and hypercharge.

This paper presents a treatment of some essential results obtained by the authors in quantum field theory with infinite multiplets. The explicit expression of the matrix of finite Lorentz transformation is found. The interaction of infinite multiplets is studied and its specific properties are shown. The quantization of fields with infinite multiplets is considered. The generalized Feynman rules are formulated.

The annihilation of antiprotons on nucleons is investigated assuming various symmetry groups. The general structure of the transition amplitude is found for the unitary symmetry and the higher symmetries SL (6, C) and U (6, 6) are applied to annihilations at rest. The relations between matrix elements, amplitudes and cross sections, following from various symmetries are compared with each other and with experiments. It is shown that all SL (6, C) predictions, that can be compared with experiments, are in good agreement, whereas the stronger results of the U (6, 6) symmetry contradict experiments.

The asymptotic behaviour of many channel amplitudes is investigated by means of Lippman-Schwinger equations with local complex potentials. It is shown that in the case of potentials without subtraction the amplitudes have a Regge behaviour with the same trajectory. The role of subtraction terms which may lead to non-Regge type behaviour is discussed.

The contributions of the cuts in the l-plane to the scattering amplitude are investigated. A way of separating the pole terms is discussed. These terms should be understood as the main ones in the expansion in powers of e 2 m(m 2 −E 2 ) −1 2 .

The renormalization of the β-decay axial constant is considered in the Chew-Low theory with fixed nucleon. The renormalization constant λ = −GA/GV is expressed in terms of the renormalized constant of pion-nucleon strong interaction and total cross sections of pion-nucleon scattering.