  We demonstrate phase locking of a 729 nm diode laser to a 1542 nm master
laser via an erbium-doped-fiber frequency comb, using a transfer-oscillator
feedforward scheme which suppresses the effect of comb noise in an
unprecedented 1.8 MHz bandwidth. We illustrate its performance by carrying out
coherent manipulations of a trapped calcium ion with 99 % fidelity even at
few-microsecond timescales. We thus demonstrate that transfer-oscillator
locking can provide sufficient phase stability for high-fidelity quantum logic
manipulation even without pre-stabilization of the slave diode laser.
