Optimal Control of a Qubit coupled to a Two-Level Fluctuator*

Experimental realizations of superconducting qubits are prone to decoherence from a fluctuating environment. An important source of charge and critical current noise are two-level fluctuators with a Lorentzian noise spectrum. We apply a recent generalization of quantum optimal control in presence of decoherence, the openGRAPE algorithm [1], to a microscopic model of a qubit coupled to a single two-level fluctuator. We find pulses that decrease the error of single qubit quantum gates and quantum memory up to a magnitude compared with conventional pulses. The qubit is pulsed in a way that the effect of the fluctuator is minimized. We investigate system and optimized pulses in various parameter regimes. [1] T. Schulte-Herbr\"uggen et al., quant-ph/0609037