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arXiv:cond-mat/0612057 · Physical Review B

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

Francesco Ciccarello, G. Massimo Palma, Michelangelo Zarcone

Published May 10, 2007• 22 citations
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Abstract

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.

DOI
10.1103/physrevb.75.205415

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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.
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.
In this paper we study the Aharonov-Bohm oscillations of transmission coefficient for an electron passing through a quantum nanoring with two identical magnetic impurities using quantum waveguide theory. It is shown that the Aharonov-Bohm oscillations are independent of the coupling constant between the electron and magnetic impurities for the singlet spin state of impurities, while for the other spin states of impurities the Aharonov-Bohm oscillations decrease rapidly with an increasing coupling constant. For a triplet spin state of impurities, we can use this system as a quantum NOT gate with an efficiency upper than 50% by adjusting the coupling constant between the electron and magnetic impurities and the magnetic flux passing through the ring.
We present a detailed analysis of the Aharonov-Bohm interference oscillations manifested through transmission of an electron in a mesoscopic ring with a magnetic impurity atom inserted in one of its arms. The electron interacts with the impurity through the exchange interaction leading to exchange spin-flip scattering. Transmission in the spin-flipped and spin-unflipped channels are explicitly calculated. We show that the spin-flipper acts as a dephasor in spite of absence of any inelastic scattering. The spin-conductance (related to spin-polarized transmission coefficient) is asymmetric in the flux reversal as opposed to the two probe conductance which is symmetric under flux reversal.
The Aharonov–Bohm (AB) interference oscillations manifested through transmission of an electron in a mesoscopic device with a double-ring in the presence of a magnetic impurity serving as the spin-flipper are studied. The spin-flipper is demonstrated to indeed cause the partial decoherence of the AB interference. Moreover, it is found that the spin-up/down transmission coefficients are asymmetric in the flux reversal while the reflection coefficients as well as that the total transmission coefficient are symmetric.
We study a simple model of dephasing of Aharonov-Bohm oscillations in the transmission of an electron across a mesoscopic ring. A magnetic impurity in one of the arms of the ring couples to the electron spin via an exchange interaction. This interaction leads to spin flip scattering and induces dephasing via entanglement. This is akin to the models evoked earlier to explain destruction of interference due to which-path information in double-slit experiments. Total transmission is found to be symmetric under flux reversal but not the spin polarization.
We study the current magnification effect in presence of exchange scattering of electron from a magnetic impurity placed in one arm of an open mesoscopic ring. The exchange interaction causes entanglement of electron spin and impurity spin. Earlier studies have shown that such an entanglement causes reduction or loss of interference in the Aharonov–Bohm oscillations leading to decoherence. We find however, that this entanglement, in contradiction to the naive expectation of a reduction in current magnification leads to enhancement as well as suppression of the effect. We also observe additional novel features like new resonances and current reversals.