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The control of quantum states is essential both for fundamental investigations and for technological applications of quantum physics. In quantum few-body systems, decoherence arising from interaction with the environment hinders the realization of desired processes. In quantum many-body systems, complexity of their dynamics further makes state preparation via external manipulation highly non-trivial. An effective strategy to counter these effects is offered by quantum optimal control theory, exploiting quantum coherence to dynamically reach a desired goal with high accuracy even under limitations on resources such as time, bandwidth, and precision. In this talk I will (i) introduce the quantum optimal control method we developed to this aim, the CRAB (Chopped Random Basis) algorithm, (ii) present experimental results obtained via its application to various physical systems, from quantum logical operations in solid-state quantum optics to quantum criticality in ultra-cold atoms, (iii) use these examples to illustrate the quantum speed limit, i.e. the maximum speed achievable for a given quantum transformation, and (iv) propose a way to characterise the latter in an information-theoretical fashion by the bandwidth of the optimized control pulses.

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Tommaso Calarco, Ulm University
TP seminar room 0.03
Contact: Achim Rosch