Single-qubit-gate error below 10^-4 in a trapped ion
  With a 9Be+ trapped-ion hyperfine-states qubit, we demonstrate an error probability per randomized single-qubit gate of 2.0(2) x 10^-5, below the threshold estimate of 10^-4 commonly considered sufficient for fault-tolerant quantum computing. The 9Be+ ion is trapped above a microfabricated surface-electrode ion trap and is manipulated with microwaves applied to a trap electrode. The achievement of low single-qubit-gate errors is an essential step toward the construction of a scalable quantum computer. 
K. R. Brown, A. C. Wilson, Y. Colombe, C. Ospelkaus, A. M. Meier, E.   Knill, D. Leibfried, and D. J. Wineland
quant-ph