Implementing high-fidelity two-qubit gates is crucial for universal quantum computation using semiconductor quantum dot qubits. This paper studies capacitive coupling between two triple quantum dot spin qubits encoded in the S=1/2, Sz=-1/2 decoherence-free subspace (exchange-only qubits). Exact gate sequences for CPHASE and CNOT gates are presented, along with theoretical demonstration of multiple two-qubit sweet spots (2QSS) in the parameter space. Two-qubit gate fidelities and times are calculated under 1/f noise, providing insights into noise thresholds for fault-tolerance. The study compares fidelities and times at single and multiple parameter 2QSS for resonant exchange (RX) and always-on exchange-only (AEON) qubits, offering a path towards high-fidelity quantum computation.

MengKe Feng, Lin Htoo Zaw, Teck Seng Koh