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The spin of a single electron in a semiconductor quantum dot provides a long-lived and well controlled quantum bit. I will first summarize our recent work on single-shot correlation measurements in double quantum dots, and on the realization of a two-qubit gate [1]. Next I will discuss new physical insights concerning single-qubit manipulation using electric-dipole spin resonance [2]. Finally, I will present in more detail unpublished work on the realization of coherent coupling between the outer dots of a triple quantum dot array. The coupling is mediated by virtual occupation of the intermediate site. We control the strength of this effective "cotunnel coupling" through the energy detuning of the intermediate levels. Since only discrete states are involved, the cotunnel coupling can generate quantum coherent dynamics. We use it to control coherent charge oscillations between the outer dots, based on Landau-Zener-Stuckelberg interference. The long-range coupling significantly improves the prospects of fault-tolerant quantum computation using quantum dot arrays and gives new perspectives for performing quantum simulations with these systems.

[1] Nowack et al, Science 333, 1269 (2011) [2] Shafiei et al, arXiv:1207.3331

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