M. Zarcone

Entanglement controlled single-electron transmittivity

We show that the electron transmittivity of single electrons propagating along a one-dimensional (1D) wire in the presence of two magnetic impurities is affected by the entanglement between the impurity spins. For suitable values of the electron wave vector, there are two maximally entangled spin states which, respectively, make the wire completely transparent whatever the electron spin state or strongly inhibit electron transmission.

Monte Carlo Analysis of the Efficiency of Tera-Hertz Harmonic Generation in Semiconductor Nitrides

The high-order harmonics generation in bulk InN, subjected to a high-frequency alternating electric field of strong-amplitude is investigated theoretically using Monte Carlo simulations of carrier interacting with a multi-mode electric field. This approach allows on the one hand to account in a natural way for the effect of the reabsorption of the generated radiation by the nonlinear medium itself, and on the other hand to estimate the constraints, which must be satisfied by the external experimental setup to achieve the maximum conversion efficiency. It is demonstrated, that InN is a promising material for such a conversion up to the THz frequency range. Under optimum conditions, the power conversion efficiency is found to reach several percents.

Electron Fabry–Perot interferometer with two entangled magnetic impurities

We consider a one-dimensional (1D) wire along which single conduction electrons can propagate in the presence of two spin-1/2 magnetic impurities. The electron may be scattered by each impurity via a contact-exchange interaction and thus a spin-flip generally occurs at each scattering event. Adopting a quantum waveguide theory approach, we derive the stationary states of the system at all orders in the electron–impurity exchange coupling constant. This allows us to investigate electron transmission for arbitrary initial states of the two impurity spins. We show that for suitable electron wave vectors, the triplet and singlet maximally entangled spin states of the impurities can respectively largely inhibit the electron transport or make the wire completely transparent for any electron spin state. In the latter case, a resonance condition can always be found, representing an anomalous behaviour compared to typical decoherence induced by magnetic impurities. We provide an explanation for these phenomena in terms of the Hamiltonian symmetries. Finally, a scheme to generate maximally entangled spin states of the two impurities via electron scattering is proposed.

Inverse bremsstrahlung in a plasma with electron temperature anisotropy

Inverse bremsstrahlung absorption of electromagnetic radiation in plasma with anisotropic two-temperature bi-Maxwellian electron distribution function over velocities is investigated. In the case of a weak field, absorption is more effective if the radiation field is polarized in the plane in which the plasma electrons have the smaller of the two temperatures. In the case when the distribution function is highly anisotropic, absorption changes strongly when the field polarization changes its direction with respect to the temperature anisotropy axis. In the intermediate domain, when the field is strong in directions not very close to that of the larger temperature, both absorption efficiency and degree of its anisotropy decrease. The conditions when the absorbed power practically does not depend on the field are established. Finally, in the case of a strong field, absorption decreases further while the degree of anisotropy is a weakly changing logarithmic function of effective electron temperatures.

Entanglement-induced electron coherence in a mesoscopic ring with two magnetic impurities

We investigate the Aharonov-Bohm (AB) interference pattern in the electron transmission through a mesoscopic ring in which two identical noninteracting magnetic impurities are embedded. Adopting a quantum waveguide theory, we derive the exact transmission probability amplitudes and study the influence of maximally entangled states of the impurity spins on the electron transmittivity interference pattern. For suitable electron wave vectors, we show that the amplitude of AB oscillations in the absence of impurities is, in fact, not reduced within a wide range of the electron-impurity coupling constant when the maximally entangled singlet state is prepared. Such state is thus able to inhibit the usual electron decoherence due to scattering by magnetic impurities. We also show how this maximally entangled state of the impurity spins can be generated via electron scattering.

A simple model of high harmonic generation in a plasma

We apply the average electron model to describe high harmonic generation in a collisional plasma in a laser field. The model is based on the coupled kinetic equations for electron velocity and electron temperature. The harmonic intensities are obtained from the Fourier coefficients of the nonlinear part of the electron velocity. Numerical calculations are reported for both strongly and weakly ionized plasmas in the nonstationary regime. We show the role of collisions frequencies as well as of quiver and thermal velocities in the harmonic generation efficiency.

CHANGES OF ELECTRONIC NOISE INDUCED BY OSCILLATING FIELDS IN BULK GaAs SEMICONDUCTORS

A Monte Carlo study of hot-electron intrinsic noise in a n-type GaAs bulk driven by one or two mixed cyclostationary electric fields is presented. The noise properties are investigated by computing the spectral density of velocity fluctuations. An analysis of the noise features as a function of the amplitudes and frequencies of two applied fields is presented. Numerical results show that it is possible to reduce the intrinsic noise. The best conditions to realize this effect are discussed.

Even harmonics generation of high frequency radiation in current-carrying plasmas

Generation of high frequency radiation harmonics in a current-carrying plasma is studied. The physical mechanism responsible for harmonics generation is provided by electron-ion collisions. The current in the plasma is sustained by a constant electric field. It is shown that the electron distribution function anisotropy due to the static field yields generation of even harmonics. As a result, the radiation spectrum emitted by the current-carrying plasma contains both even and odd harmonics, the latter being attributed to currentless plasma. For a broad range of plasma and high frequency radiation parameters, a detailed analysis of the even harmonics properties is reported.

Monte Carlo simulation of harmonic generation in InP

Harmonics spectra in an n-type InP bulk semiconductor showing up to the 13th harmonic are reported. The external field is linearly polarized with the frequency v = 100 GHz. Calculations are based on a Monte Carlo simulation for the electron motion in the conducting band and on an electrodynamics equation for the harmonics generation. The effect of a significant reduction of efficiency in the generation of particular harmonics is found, and is traced back to a sort of alternating field Gunn effect. A short analysis of the different physical mechanisms giving rise to harmonics generation is presented.

Quasideterministic realization of a universal quantum gate in a single scattering process

We show that a flying particle, such as an electron or a photon, scattering along a one-dimensional waveguide from a pair of static spin-1/2 centers, such as quantum dots, can implement a controlled-z gate (universal for quantum computation) between them. This occurs quasideterministically in a single scattering event, with no need for any postselection or iteration and without demanding the flying particle to bear any internal spin. We show that an easily matched hard-wall boundary condition along with the elastic nature of the process are key to such performances.