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      Dephasing in the adiabatic rapid passage in quantum dots: the role of phonon-assisted biexciton generation

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          Abstract

          We study the evolution of an exciton confined in a quantum dot adiabatically controlled by a frequency-swept (chirped) laser pulse in the presence of carrier-phonon coupling. We focus on the dynamics induced by a linearly polarized beam and analyze the decoherence due to phonon-assisted biexciton generation. We show that if the biexciton state is shifted down by a few meV, as is typically the case, the resulting decoherence is strong even at low temperatures. As a result, efficient state preparation is restricted to a small parameter area corresponding to low temperatures, positive chirps and moderate pulse areas.

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          Coherent properties of a two-level system based on a quantum-dot photodiode.

          Present-day information technology is based mainly on incoherent processes in conventional semiconductor devices. To realize concepts for future quantum information technologies, which are based on coherent phenomena, a new type of 'hardware' is required. Semiconductor quantum dots are promising candidates for the basic device units for quantum information processing. One approach is to exploit optical excitations (excitons) in quantum dots. It has already been demonstrated that coherent manipulation between two excitonic energy levels--via so-called Rabi oscillations--can be achieved in single quantum dots by applying electromagnetic fields. Here we make use of this effect by placing an InGaAs quantum dot in a photodiode, which essentially connects it to an electric circuit. We demonstrate that coherent optical excitations in the quantum-dot two-level system can be converted into deterministic photocurrents. For optical excitation with so-called pi-pulses, which completely invert the two-level system, the current is given by I = fe, where f is the repetition frequency of the experiment and e is the elementary charge. We find that this device can function as an optically triggered single-electron turnstile.
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            Coherent control of a single exciton qubit by optoelectronic manipulation

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              Author and article information

              Journal
              2012-09-12
              Article
              1209.2675
              8cfb94a5-1f4a-4c4b-926c-fe0d0d8468e2

              http://arxiv.org/licenses/nonexclusive-distrib/1.0/

              History
              Custom metadata
              Phys. Rev. B 86, 235301 (2012)
              5 pages, 5 figures
              cond-mat.mes-hall

              Nanophysics
              Nanophysics

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