Reduced phase error through optimized control of a superconducting qubit

Minimizing phase and other errors in experimental quantum gates allows higher fidelity quantum processing. To quantify and correct for phase errors, in particular, we have developed an experimental metrology - amplified phase error (APE) pulses - that amplifies and helps identify phase errors in general multilevel qubit architectures. In order to correct for both phase and amplitude errors specific to virtual transitions and leakage outside of the qubit manifold, we implement 'half derivative', an experimental simplification of derivative reduction by adiabatic gate (DRAG) control theory. The phase errors are lowered by about a factor of five using this method to {approx}1.6 deg. per gate, and can be tuned to zero. Leakage outside the qubit manifold, to the qubit |2> state, is also reduced to {approx}10{sup -4} for 20% faster gates.