  The key to realizing fault-tolerant quantum computation for singlet-triplet
(ST) qubits in semiconductor double quantum dot (DQD) is to operate both the
single- and two-qubit gates with high fidelity. The feasible way includes
operating the qubit near the transverse sweet spot (TSS) to reduce the leading
order of the noise, as well as adopting the proper pulse sequences which are
immune to noise. The single-qubit gates can be achieved by introducing an AC
drive on the detuning near the TSS. The large dipole moment of the DQDs at the
TSS has enabled strong coupling between the qubits and the cavity resonator,
which leads to a two-qubit entangling gates. When operating in the proper
region and applying modest pulse sequences, both single- and two-qubit gates
are having fidelity higher than 99%. Our results suggest that taking advantage
of the appropriate pulse sequences near the TSS can be effective to obtain
high-fidelity ST qubits.
