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 interqubit 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 similar to 5 ns, and zero-controlled-NOT gates of length similar to 7 ns, both with fidelities >99.9%.