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International Conference on Solid State Devices and Materials (SSDM)

Formation and control of 2-qubits exciton state in a coupled quantum dots.

Keishiro Goshima, Kazuhiro Komori, Takeyoshi Sugaya

Published Sep 18, 2007• 0 citations
Publisher
DOI
10.7567/ssdm.2007.i-9-5

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We investigated the formation dynamics of an artificial exciton molecule state, which consists of two different excitons confined in each quantum dot of a pair of quantum dots, namely, a coupled quantum dot (CQD). By the selective optical excitation of the inherent energy states of two different excitons using two-color pulsed excitation, we created an artificial exciton molecule state and investigated the transient dynamics, and monitored the photoluminescence, namely, the population of the artificial exciton molecule states. By employing the power dependence of the two colors, we tried the two-qubit logic gate operation and succeeded in controlling the population of an artificial exciton molecule (pulse area θ<π).
Controlled non-local energy and coherence transfer enables light harvesting in photosynthesis and non-local logical operations in quantum computing. This process is intuitively pictured by a pair of mechanical oscillators, coupled by a spring, allowing for a reversible exchange of excitation. On a microscopic level, the most relevant mechanism of coherent coupling of distant quantum bits—like trapped ions, superconducting qubits or excitons confined in semiconductor quantum dots—is coupling via the electromagnetic field. Here we demonstrate the controlled coherent coupling of spatially separated quantum dots via the photon mode of a solid state microresonator using the strong exciton–photon coupling regime. This is enabled by two-dimensional spectroscopy of the sample’s coherent response, a sensitive probe of the coherent coupling. The results are quantitatively understood in a rigorous description of the cavity-mediated coupling of the quantum dot excitons. This mechanism can be used, for instance in photonic crystal cavity networks, to enable a long-range, non-local coherent coupling. Controlling coupling between distant quantum objects is important for implementation of quantum technologies. Providing an important step towards using semiconductor structures for hosting optically controlled qubits, this work shows coherent coupling between three quantum dot excitons via a cavity.