Curator's Take
This research addresses a crucial challenge in scaling quantum computers by demonstrating that fluxonium qubits can achieve fast, high-fidelity two-qubit gates using only capacitive coupling - potentially simplifying chip fabrication compared to current approaches that require inductive couplings. The finding that CNOT gates can be executed in under 200 nanoseconds while maintaining low crosstalk represents a significant speed advantage that could reduce decoherence errors in quantum algorithms. Perhaps most importantly for practical quantum computing, the study shows that fluxonium-based architectures are much less sensitive to the inevitable manufacturing variations that plague current transmon-based systems, potentially leading to higher yields and more reliable quantum processors. This work strengthens the case for fluxonium qubits as a viable alternative to the dominant transmon technology, offering a pathway toward more robust and scalable quantum hardware.
— Mark Eatherly
Summary
We study the cross-resonance effect in capacitively-coupled fluxonium qubits and devise a simple formula for their maximum ZX interaction strength. By going beyond the perturbative regime, we find that a CNOT gate can generally be realized in under 200 ns with residual ZZ limited to 50 kHz, for fluxonium qubits with frequencies below 1 GHz. Our analysis relies on a semi-analytical method: we first numerically diagonalize the Floquet Hamiltonian of the strongly-driven control qubit and then perturbatively incorporate the weak qubit-qubit coupling to obtain an effective Hamiltonian. We also derive frequency collision windows around harmful control-target and control-spectator transitions. For large fluxonium devices, we predict a collision-free yield that is considerably less sensitive to junction variability compared to transmons in the same layout. These results support the viability of an all-fluxonium cross-resonance architecture with only capacitive couplings.