(color online) High fidelity universal quantum gate implemented by optimal composite pulses. (a) and (b) Gate fidelity of an original gradient ascent pulse engineering (GRAPE) (a) and a modified one (b). The upper figures are the contour maps of the gate fidelity. The modified GRAPE is more robust to the noise effects and pulse errors. A CNOT gate with fidelity of 0.992 is achieved with this modified GRAPE. (c) The used pulse parameters of the optimal control experiment. The left (right) one is the amplitude (phase) sequence. Reproduced from Ref. [33], NPG.