Coherent few-electron spin-states in graphene nanoribbons from ab initio

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Graphene nanoribbons (GNR) offer various promising paths towards the realization of spin-based quantum register systems. One is the preparation of quantum dots. Besides single-electron states in an isolated quantum dot, two-electron singlet-triplet states of a coupled double-quantum-dot system represent suitable two-level quantum- bit realizations. In any case, spin coherence processes play a crucial role for the operation of a quantum gate. The project addresses this realization, aiming predominantly at the theoretical understanding of spin states and their dynamics in coupled quantum-dot structures. Here, we focus on a few-electron prototype system, based on a one-dimensional structure, which is realized as a graphene nanoribbon. As a novel approach, realistic nanodevice simulations are being carried out, combining an ab-initio theory (density-functional theory, DFT) for the determination of the matrix elements with a subsequent diagonalization in the relevant subspace (“configuration interaction”, CI). Hence, material- and geometry-specific aspects of the considered nanoelectronic system are taken into account. Since excited many-body states will be included, the real-time response of the few electron spin system can be calculated – inherently considering coherence and many-body correlation aspects.