Single-qubit-gate error below 10-4 in a trapped ion

With a Be-9(+) trapped-ion hyperfine-state 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 Be-9(+) 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.