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arXiv:cond-mat/0412653 · Physical Review A

Entanglement and quantum-state engineering in the optically driven two-electron double-dot structure

Alexander V. Tsukanov

Published Aug 30, 2005• 29 citations
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Abstract

We study theoretically the quantum dynamics of two interacting electrons in the symmetric double-dot structure under the influence of a bichromatic resonant pulse. The state vector evolution is studied for two different pulse designs. It is shown that the laser pulse can generate an effective exchange coupling between electron spins localized in different dots. Possible applications of this effect to quantum-information processing (entanglement generation, quantum-state engineering) are discussed.

DOI
10.1103/physreva.72.022344

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We study theoretically the quantum dynamics of two interacting electrons in the symmetric double-dot structure under the influence of a bichromatic resonant pulse. The state vector evolution is studied for two different pulse designs. It is shown that the laser pulse can generate an effective exchange coupling between electron spins localized in different dots. Possible applications of this effect to quantum-information processing (entanglement generation, quantum-state engineering) are discussed.
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Recently, an implementation of a universal set of one- and two-quantum-bit gates for quantum computation using spin states of coupled single-electron quantum dots was proposed. It was demonstrated that it is possible to execute a coherent control of a quantum system based on two-electron spin states in a double quantum dot, allowing state preparation, coherent manipulation, and projective readout. This possibility is based on rapid electrical control of the spin exchange interaction. These results motivated us to develop a formal theoretical study of the corresponding model of two coupled spins placed in a magnetic field and subjected to a time-dependent mutual Heisenberg interaction. Using possible exact solutions of the corresponding quantum problem, we study entangling of different separable initial states in this model. It is demonstrated that the entanglement due to a time-dependent Heisenberg interaction is dominating in comparison with the entanglement due to the action of an external magnetic field.
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In this paper, by applying generalized density-matrix equations, we explore the ultrafast dynamics of photo-generated electron–hole pairs in the system composed of electromagnetically coupled GaAs/AlGaAs quantum dots and reveal the physics mechanism behind laser-controlled nonlinear-optical response of electron–hole pairs. For the single-dot system, we present numerical results to show the transient dependence of carrier occupations and induced quantum coherence of electron–hole pairs in the presence of either a single or double laser pulses, as well as for a step turning-on of the laser field. For a dipole-radiation coupled double-dot system, we study numerically the time dependence of both intradot and interdot self-consistent depolarization fields within and between two dots, respectively. Meanwhile, we further demonstrate the significance of phase matching between induced depolarization fields and incident-laser pulse in order to maximize the stimulated transitions of electron–hole pairs and ensure non-quenched Rabi oscillations in each quantum dot. The employed theoretical model and the associated numerical analysis method are expected to facilitate designing and developing artificial quantum molecules composed of arbitrarily dielectric-embedded quantum dots with non-local quantum interactions and entanglement, as well as optically manipulating electron states of artificial quantum molecules.
We study theoretically the quantum dynamics of an electron in the singly ionized double-donor structure in the semiconductor host under the influence of laser pulses whose frequencies are close to structure resonant frequencies. This system can be used as a charge qubit where the logical states are defined by the lowest two energy states of the remaining valence electron localized around one or another donor. The quantum operations are performed via resonant or Raman-like transitions between the localized (qubit) states and the excited states delocalized over the structure, combined with phase shifts between qubit states generated by voltage pulses. The possibility of realization of arbitrary single-qubit rotations is demonstrated.