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Coherent manipulation of charge qubits in double quantum dots

Alexander Croy, Ulf Saalmann

Published Apr 12, 2011• 6 citations
OpenAlex

Abstract

Abstract. The coherent time evolution of electrons in double quantum dots induced by fast bias-voltage switches is studied theoretically. As it was shown experimentally, such driven double quantum dots are potential devices for controlled manipulation of charge qubits. By numerically solving a quantum master equation we obtain the energy- and time-resolved electron transfer through the device which resembles the measured data. The observed oscillations are found to depend on the level offset of the two dots during the manipulation and, most surprisingly, also the on initialization stage. By means of an analytical expression, obtained from a large-bias model, we can understand the prominent features of these oscillations seen in both the experimental data and the numerical results. These findings strengthen the common interpretation in terms of a coherent transfer of electrons between the dots. PACS numbers: 73.63.Kv,73.23.Hk,72.10.-d

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Abstract. The coherent time evolution of electrons in double quantum dots induced by fast bias-voltage switches is studied theoretically. As it was shown experimentally, such driven double quantum dots are potential devices for controlled manipulation of charge qubits. By numerically solving a quantum master equation we obtain the energy- and time-resolved electron transfer through the device which resembles the measured data. The observed oscillations are found to depend on the level offset of the two dots during the manipulation and, most surprisingly, also the on initialization stage. By means of an analytical expression, obtained from a large-bias model, we can understand the prominent features of these oscillations seen in both the experimental data and the numerical results. These findings strengthen the common interpretation in terms of a coherent transfer of electrons between the dots. PACS numbers: 73.63.Kv,73.23.Hk,72.10.-d
The coherent time evolution of electrons in double quantum dots (DQDs) induced by fast bias-voltage switches is studied theoretically. As it was shown experimentally, such driven DQDs are potential devices for controlled manipulation of charge qubits. By numerically solving a quantum master equation, we obtain the energy- and time-resolved electron transfer through the device that resembles the measured data. The observed oscillations are found to depend on the level offset of the two dots during the manipulation and, most surprisingly, also the initialization stage. By means of an analytical expression, obtained from a large-bias model, we can understand the prominent features of these oscillations seen in both the experimental data and the numerical results. These findings strengthen the common interpretation in terms of a coherent transfer of electrons between the dots.
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.