High-fidelity gates in a Josephson qubit
  We demonstrate new experimental procedures for measuring small errors in a superconducting quantum bit (qubit). By carefully separating out gate and measurement errors, we construct a complete error budget and demonstrate single qubit gate fidelities of 0.98, limited by energy relaxation. We also introduce a new metrology tool -- a Ramsey interference error filter -- that can measure the occupation probability of the state $\ket{2}$ down to $10^{-4}$, a magnitude near the fault tolerant threshold. 
Erik Lucero (1), M. Hofheinz (1), M. Ansmann (1), Radoslaw C. Bialczak   (1), N. Katz (1 and 2), Matthew Neeley (1), A. D. O...