High-Fidelity Entangling Gates for Quantum-Dot Hybrid Qubits Based on Exchange Interactions

Quantum dot hybrid qubits exploit an extended charge-noise sweet spot that suppresses dephasing and has enabled the experimental achievement of high-fidelity single-qubit gates. However, current proposals for two-qubit gates require tuning the qubits away from their sweet spots. Here, we propose a two-hybrid-qubit coupling scheme, based on exchange interactions, that allows the qubits to remain at their sweet spots at all times. The interaction is controlled via the inter-qubit tunnel coupling. By simulating such gates in the presence of realistic quasistatic and $1\!/\!f$ charge noise, we show that our scheme should enable controlled-$Z$ gates of length $\sim$5~ns, and Z-CNOT gates of length $\sim$7~ns, both with fidelities $>$99.9\%.