We show that the electron transmittivity of single electrons propagating along a 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 inhibits electron transmission.

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

We present a protocol that sets maximum stationary entanglement between remote spins through scattering of mobile mediators without initialization, post-selection or feedback of the mediators' state. No time-resolved tuning is needed and, counterintuitively, the protocol generates two-qubit singlet states even when classical mediators are used. The mechanism responsible for such effect is resilient against non-optimal coupling strengths and dephasing affecting the spins. The scheme uses itinerant particles and scattering centres and can be implemented in various settings. When quantum dots and photons are used a striking result is found: injection of classical mediators, rather than quantum ones, improves the scheme efficiency.

We investigate whether a two-qubit quantum gate can be implemented in a scattering process involving a flying and a static qubit. To this end, we focus on a paradigmatic setup made out of a mobile particle and a quantum impurity, whose respective spin degrees of freedom couple to each other during a one-dimensional scattering process. Once a condition for the occurrence of quantum gates is derived in terms of spin-dependent transmission coefficients, we show that this can be actually fulfilled through the insertion of an additional narrow potential barrier. An interesting observation is that under resonance conditions this procedure enables a gate only for isotropic Heisenberg (exchange) interactions and fails for an XY interaction. We show the existence of parameter regimes for which gates able to establish a maximum amount of entanglement can be implemented. The gates are found to be robust to variations of the optimal parameters.

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.

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.

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In a recent paper -F. Ciccarello et al., New J. Phys. 8, 214 (2006) -we have demonstrated that the electron transmission properties of a one-dimensional (1D) wire with two identical embedded spin-1/2 impurities can be significantly affected by entanglement between the spins of the scattering centers. Such effect is of particular interest in the control of transmission of quantum information in nanostructures and can be used as a detection scheme of maximally entangled states of two localized spins. In this letter, we relax the constraint that the two magnetic impurities are equal and investigate how the main results presented in the above paper are affected by a static disorder in the exchange coupling constants of the impurities. Good robustness against deviation from impurity symmetry is found for both the entanglement dependent transmission and the maximally entangled states generation scheme.PACS numbers: 03.67. Mn, 85.35.Ds The key role that entanglement plays in quantum information processing has been investigated over the past few years [1]. In this framework, the role that it plays in quantum transport in mesoscopic systems has been analyzed [2]. Recently, we have shown a novel way in which entanglement can be used for controlling electron transport in nanostructures [3]. Assume to have a 1D wire where two spin-1/2 impurities are embedded at a fixed distance. Such system can be regarded as the electron analogue of a Fabry-Perot (FP) interferometer, with the impurities playing the role of two mirrors with a spin quantum degree of freedom. Single electrons are injected into the wire and undergo multiple scattering between the two magnetic impurities due to the presence of a contact exchange electron-impurity coupling. At each scattering event spin-flip may occur and thus the transmitted spin state of the overall system will be generally different from the incoming one. The typical behaviour shown by electron transmittivity T consists of a loss of electron coherence and thus of a resonance condition T = 1, due to the presence of internal spin degrees of freedom of the scattering centers [4]. Such a system is indeed the electron analogue of a Fabry-Perot (FP) interferometer, with the impurities playing the role of two mirrors with a spin quantum degree of freedom. However, unlike the standard FP device where scattering with each mirror introduces a well-fixed phase shift, in the present system the above phase shifts depend on the electron-impurities spin state and thus, in general, a resonance condition cannot take place. However, the presence of quantum scatterers allows one to investigate if and to what extent maximally entangled states of the impurity spins can affect electron transmission. Denot-ing by |Ψ ± = 2 − 1 2 (|↑↓ ± |↓↑ ) the triplet and singlet maximally entangled spin states of the impurities, respectively, we have thus found that when |Ψ − is prepared, a perfect resonance condition T = 1 can be always reached at electron wave vectors fulfilling kx 0 = nπ (n integer, x 0 the distance between...