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Journal of Applied Physics

Coherent single-electron transfer in coupled quantum dots

Antonios Fountoulakis, Andreas Terzis, Emmanuel Paspalakis

Published Oct 1, 2009• 26 citations
Publisher

Abstract

We theoretically investigate the coherent transfer of one electron between the ground states of a double coupled quantum dot structure. The coherent transfer of the electron is externally controlled by applied electromagnetic fields with on- or close-resonance driving frequencies and various shapes and duration. We derive the analytical expressions for the parameters of the external fields by approximating the quantum dot system as a three-level Λ-type system. The analytical solutions are compared with numerical results and good agreement is found. The control methods developed here are applicable in symmetric and asymmetric quantum dot nanostructures.

DOI
10.1063/1.3232226

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We theoretically investigate the coherent transfer of one electron between the ground states of a double coupled quantum dot structure. The coherent transfer of the electron is externally controlled by applied electromagnetic fields with on- or close-resonance driving frequencies and various shapes and duration. We derive the analytical expressions for the parameters of the external fields by approximating the quantum dot system as a three-level Λ-type system. The analytical solutions are compared with numerical results and good agreement is found. The control methods developed here are applicable in symmetric and asymmetric quantum dot nanostructures.
We study the potential for coherent transfer of a single electron between the ground states of two anharmonic coupled quantum dots using an adiabatic passage method. We consider the interaction of a quantum dot structure characterized by an asymmetric confining potential by two external electromagnetic fields. We use the method of stimulated Raman adiabatic passage (STIRAP) for control of the dynamics of the electron, and ultimately for succeeding the transfer of the electron from the initially occupied quantum dot to the other quantum dot. Results for several values of the parameters of the applied electromagnetic fields are presented, and we show that STIRAP can lead to efficient coherent single electron transfer for a wide range of these parameters.
Abstract Semiconductor quantum dots are ideal candidates for quantum information applications in solid-state technology. However, advanced theoretical and experimental tools are required to coherently control, for example, the electronic charge in these systems. Here we demonstrate how quantum optimal control theory provides a powerful way to manipulate the electronic structure of coupled quantum dots with an extremely high fidelity. As alternative control fields we apply both laser pulses as well as electric gates, respectively. We focus on double and triple quantum dots containing a single electron or two electrons interacting via Coulomb repulsion. In the two-electron situation we also briefly demonstrate the challenges of timedependent density-functional theory within the adiabatic local-density approximation to produce comparable results with the numerically exact approach.
A theoretical study of the effect of a resonance electromagnetic pulse on the coherent electron dynamics in a system of tunneling-coupled quantum dots (QDs) arranged in a closed-ring configuration is carried out. It is shown that selective electron transfer between two arbitrary QDs is possible. The transfer probability is calculated as a function of the parameters that characterize the QDs and the electromagnetic pulse. It is shown that this probability can be close to unity. Factors leading to a reduction of the transfer probability in a realistic system are considered. The results obtained can be used for the development of new types of nanoelectronic devices for performing operations with quantum bits.
We study the potential for optimal control of a symmetric double quantum-dot structure interacting with a single pulsed electromagnetic field. We first use the rotating wave and resonant approximations and reduce the dynamics of the system to that of a degenerate three-level $\ensuremath{\Lambda}$-type system. We also formulate the optimal control problem in terms of differential equations that have to be fulfilled by the optimal electromagnetic fields. We then obtain general analytical expressions for the optimal pulse shapes that lead to global maximization of the final population of the target state and of the time-averaged population of the target state in the quantum-dot structure.
A method of coherent manipulation of the electron tunneling in quantum dots is proposed, which utilizes the quantum interference in nonadiabatic double crossing of the discrete energy levels. In this method, we need only a smoothly varying gate voltage to manipulate electrons, without a sudden switching on and off. A systematic design of a smooth gate pulse is presented with a simple analytic formula to drive the two-level electronic state to essentially an arbitrary target state, and numerical simulations for complete transfer of an electron is shown for coupled double quantum dots and an array of quantum dots. Estimation of the manipulation time shows that the present method can be employed in realistic quantum dots.