Long-range two-hybrid-qubit gates mediated by a microwave cavity with red sidebands

Implementing two-qubit gates via strong coupling between quantum-dot qubits and a superconducting microwave cavity requires achieving coupling rates that are much faster than decoherence rates. Typically, this involves tuning the qubit either to a sweet spot, where it is relatively insensitive to charge noise, or to a point where it is resonant with the microwave cavity. Unfortunately, such operating points seldom coincide. Here we theoretically investigate protocols, based on transverse or longitudinal sideband driving, for implementing two-qubit gates between quantum-dot hybrid qubits, mediated by a microwave cavity. The rich physics in these qubits gives rise to two types of sweet spots, which can occur at operating points with strong charge dipole moments. Such strong interactions provide new opportunities for off-resonant gating, thereby removing one of the main obstacles for long-distance two-qubit gates. We find that the transverse driving scheme yields faster gates, while longitudinal driving yields gates that are more resilient to photon decay. Our results suggest that the numerous tuning knobs of quantum-dot hybrid qubits make them good candidates for strong coupling. In particular, we show that off-resonant red-sideband-mediated two-qubit gates can exhibit fidelities greater than 95% for realistic operating parameters, and we describe improvements that could potentially yield gate fidelities greater than 99%.

Automated summary

Implementing two-qubit gates via strong coupling between quantum-dot qubits and a superconducting microwave cavity is challenging due to the need for coupling rates faster than decoherence rates. This study investigates protocols for two-qubit gates mediated by a microwave cavity, leading to the discovery of two different types of sweet spots in quantum-dot hybrid qubits with strong charge dipole moments. The results show that transverse driving yields faster gates, while longitudinal driving produces gates that are more resilient to photon decay. The numerous tuning knobs of quantum-dot hybrid qubits make them ideal candidates for strong coupling, with potential gate fidelities exceeding 99%.