  We study the decoherence effect of charge noise on a single flip-flop qubit
and two dipole-coupled qubits. We find that a single flip-flop qubit is highly
resistant to charge noise at its sweet spots. However, due to the proximity of
the charge excited states to the flip-flop logical states, the presence of
charge noise greatly reduces the fidelity of two-qubit operations. We identify
leakage from the qubit Hilbert space as the main culprit for the reduced gate
fidelity. We also explore different bias conditions to mitigate this
decoherence channel.
