Hybrid optimization schemes for quantum control
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In: EPJ quantum technology 2 / 21 (2015) , S. S. 1-16;
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Optimal control theory is a powerful tool for solving control problems in quantum mechanics, ranging from the control of chemical reactions to the implementation of gates in a quantum computer. Gradient-based optimization methods are able to find high fidelity controls, but require considerable numerical effort and often yield highly complex solutions. We propose here to employ a two-stage optimization scheme to significantly speed up convergence and achieve simpler controls. The control is initially parametrized using only a few free parameters, such that optimization in this pruned search space can be performed with a simplex method. The result, considered now simply as an arbitrary function on a time grid, is the starting point for further optimization with a gradient-based method that can quickly converge to high fidelities. We illustrate the success of this hybrid technique by optimizing a geometric phase gate for two superconducting transmon qubits coupled with a shared transmission line resonator, showing that a combination of Nelder-Mead simplex and Krotov’s method yields considerably better results than either one of the two methods alone.
@article{urn:nbn:de:hebis:34-2016011949686, author ={Goerz, Michael H. and Whaley, K. Birgitta and Koch, Christiane P.}, title ={Hybrid optimization schemes for quantum control}, copyright ={https://rightsstatements.org/page/InC/1.0/}, language ={en}, journal ={EPJ quantum technology}, year ={2015} }