Optically controlled exciton dynamics in coupled quantum dots is studied. We show that the maximally entangled Bell states and Greenberger-Horne-Zeilinger (GHZ) states can be robustly generated by manipulating the sys...
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Optically controlled exciton dynamics in coupled quantum dots is studied. We show that the maximally entangled Bell states and Greenberger-Horne-Zeilinger (GHZ) states can be robustly generated by manipulating the system parameters to be at the avoided crossings in the eigenenergy spectrum. The analysis of population transfer is systematically carried out by using a dressed-state picture. In addition to the quantum dot configuration that has been discussed by Quiroga and Johnson [Phys. Rev. Lett. 83, 2270 (1999)], we show that the GHZ states also may be produced in a ray of three quantum dots with a shorter generation time.
We have extended our research to the study of near-field polarization effects arising from the planar chirality. The interaction between the neighboring elements in a metallic structure can be visualized with near-fie...
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In order to study spin-wave excitations of itinerant ferromagnets a relativistic first-principles method based on the adiabatic approach is presented. The derivatives of the free energy up to second order with respect...
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In order to study spin-wave excitations of itinerant ferromagnets a relativistic first-principles method based on the adiabatic approach is presented. The derivatives of the free energy up to second order with respect of the polar and azimuthal angles are derived within the framework of the magnetic force theorem and the fully relativistic Korringa-Kohn-Rostoker method. Exchange and spin-orbit coupling are thus incorporated on equal footing in the Hamiltonian. Furthermore, a detailed comparison to classical spin Hamiltonians is given and it is shown that the magnetocrystalline anisotropy energy contains contributions from both the on-site anisotropy and the off-site exchange coupling terms. The method is applied to an Fe monolayer on Cu(001) and Au(001) surfaces and for a Co monolayer on Cu(001). The calculations provide with the gap at zero wave number due to the spin-orbit coupling and uniaxial anisotropy energies in good agreement with the results of the band energy difference method. It is pointed out that the terms in the spin-wave Hamiltonian related to the mixed partial derivatives of the free energy, absent within a nonrelativistic description, introduce an asymmetry in the magnon spectrum with respect to two in-plane easy axes. Moreover, in the case of an in-plane magnetized system the long-wavelength magnons are elliptically polarized due to the difference of the second-order uniaxial and fourth-order in-plane magnetic anisotropy.
We propose a method suitable to describe electrical transport properties of nanostructures. In this approach a Green’s function embedding technique based on the fully relativistic spin-polarized Korringa-Kohn-Rostoke...
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We propose a method suitable to describe electrical transport properties of nanostructures. In this approach a Green’s function embedding technique based on the fully relativistic spin-polarized Korringa-Kohn-Rostoker method and the coherent potential approximation is combined with a real-space formulation of the Kubo-Greenwood equation. We present calculations for the Ag(100) surface, Ag bulk, two types of CuPt bulk alloys in the “large cluster” limit as well as finite Fe and Co chains embedded into the surface layer of Ag(100) in order to illustrate the reliability and applicability of this approach.
Using a group-theoretic approach, we investigate some new peculiar features of a general quartic anharmonic oscillator. When the coefficient of the quartic term is positive and the potential is differentiable, we find...
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Using a group-theoretic approach, we investigate some new peculiar features of a general quartic anharmonic oscillator. When the coefficient of the quartic term is positive and the potential is differentiable, we find that continuity of the derivative of the potential forces the nonexistence of an analytic wave function. For the case in which the coefficient of the quartic term is negative, we find that normalizability of the wave function requires non-Hermiticity of the Hamiltonian. Finally, we apply our method to gain some insight on the double well potential.
By using the Kubo-Greenwood formula in combination with the fully relativistic spin-polarized Screened Korringa-Kohn-Rostoker method and the Coherent Potential Approximation we calculated the residual resistivity and ...
By using the Kubo-Greenwood formula in combination with the fully relativistic spin-polarized Screened Korringa-Kohn-Rostoker method and the Coherent Potential Approximation we calculated the residual resistivity and the anisotropic magnetoresistance of bulk Ni1−cFec alloys in the Ni-rich regime. While the calculated residual resistivities are typically 30–40% smaller than the measured values, for the anisotropic magnetoresistance ratios we obtained an excellent agreement between theory and experiment. Varying the angle between the directions of the magnetization and of the current we found a functional dependence of the resistivity consistent with the formula proposed originally by Döring.
In terms of the nonlinear coupled equations that describe the evolution of the radiation field and electrons motion in the magnetically insulated transmission line oscillator, the nonlinear instabilities existing in t...
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In terms of the nonlinear coupled equations that describe the evolution of the radiation field and electrons motion in the magnetically insulated transmission line oscillator, the nonlinear instabilities existing in the process of the interaction between the electron beam and field are analyzed. It is shown that the development of the instability leads to the appearance of the nonlinear behavior of the radiation field. (1) In the soft nonlinear regime in which the radiation field is characterized by the periodic limit cycle, the power spectrum is discrete and the sideband is not symmetric around the carrier frequency; in the hard nonlinear regime in which the radiation field is characterized by the chaotic oscillation, the power spectrum is continuous and the spectral components with larger amplitude distribute in the low frequency region. (2) The threshold current at which the limit cycle or chaotic oscillation starts occurring is a function of the detuning. The appearance of the nonlinear unsteady states may be accelerated and inhibited by controlling detuning. (3) The arising of the limit cycle oscillation and chaotic behavior of the radiation field is easier in a magnetically insulated transmission line oscillator than in a traveling wave tube amplifier.
The electronic and magnetic properties of the Fe/Cr/Fe systems are studied within the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method by performing calculations for varying spacer thickness. T...
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The electronic and magnetic properties of the Fe/Cr/Fe systems are studied within the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method by performing calculations for varying spacer thickness. The obtained interlayer exchange coupling shows a 2 ML period as well as phase slips due to the spin-density wave (SDW). In agreement with experimental findings we are able to prove that Mn impurities destroy the spin-density wave, whereby a statistically disordered Cr-Mn alloy spacer exhibits substantially larger effects than an atomic Mn layer separating the Cr spacer from the Fe leads. Using for such a layer V instead of Mn the SDW survives, but leads to a phase shift. The 2 ML period remains if an in-between layer of Mn or V is considered, whereas in the case of alloy formation in the spacer a superposition of different periods occurs. Further effort has been devoted to investigate the transport properties of the Fe/Cr/Fe sandwiches in the current perpendicular to the plane geometry in order to examine possible differences in the giant magnetoresistance due to the above-mentioned changes in the interlayer exchange coupling. From the present investigations we are able to show that the changes in the magnetic coupling, e.g., periods of oscillations or shifts, can directly be observed in the giant magnetoresistance.
The Boussinesq approximation, where the viscosity depends polynomially on the shear rate, finds more and more frequent use in geological practice. In this article, we consider the periodic initial value problem and in...
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