Realistic superconducting qubits are necessarily imperfect. In particular, they are not rigorous two-state systems, and they contain slow noise sources. In principle, weakly driven Rabi pulses at the optimum point can accomodate both imperfections to a certain extent on the expense of being slow. We are applying the openGRAPE (open systems gradient ascent pulse engineering) method to both problem, looking for optimal pulse shapes dealing with these challenges. It is shown that gates with near-unit fidelity can be achieved in a time set by the difference of the Ramsey frequencies of the working and leakage transition in a three-qubit system. This result can be understood as a composite pulse refocusing unwanted drifts in the rotating frame. In the presence of slow noise, it is shown how short modulated Rabi pulses corrected for counterrotating terms allow for the elimination of the impact of phase noise even when the coupling to one of the noise sources is strong, finding that telegraph noise can be corrected if it is faster or slower than the qubit precession.
Room 449, Theresienstr. 37 / IV, LMU