  Improving gate performance is vital for scalable quantum computing. The
universal quantum computing also requires the gate fidelity to reach a high
level. For superconducting quantum processor, which operates in the microwave
band, the single-qubit gates are usually realized with microwave driving. The
crosstalk between microwave pulses is a non-negligible error source. In this
article, we propose an error mitigation scheme to address this crosstalk issue
for single-qubit gates. There are three steps in our method. First, by
controlling the detuning between qubits, the microwave induced classical
crosstalk error can be constrained within the computational subspace. Second,
by applying the general decomposition procedure, arbitrary single-qubit gate
can be decomposed as a sequence of $\sqrt{X}$ and virtual Z gates. Finally, by
optimizing the parameters in virtual Z gates, the error constrained in the
computational space can be corrected. Using our method, no additional
compensation signals are needed, arbitrary single-qubit gate time will not be
prolonged, and the circuit depth containing simultaneous single-qubit gates
will also not increase. The simulation results show that, in specific regime of
qubit-qubit detuning, the infidelities of simultaneous single-qubit gates can
be as low as which without microwave crosstalk.
