Curator's Take
AI Commentary
This article shows that a single‑junction “multiunimon” can host three qubits and execute any of the twelve controlled‑controlled‑NOT gates with simulated fidelities around 99.5% using only simple sine‑squared pulses, essentially turning a modest superconducting element into a highly connected multi‑qubit module. By delivering native three‑body interactions without the overhead of sequential two‑qubit gates, it promises to shrink circuit depth for NISQ algorithms such as variational chemistry or error‑mitigation schemes, complementing recent advances in parametric and cross‑resonance entangling methods. The results remain simulation‑based and are presently limited by dielectric loss, but the projected path toward 99.99% fidelity suggests a realistic route to more compact, low‑error processors as hardware designs improve.
— Mark Eatherly
Summary
Quantum processors with native multi-qubit gates may offer very efficient implementations of near-term quantum algorithms on noisy hardware. Here, we introduce the multiunimon, a superconducting multimode circuit that encodes multiple qubits and enables native multi-qubit gates in a device consisting of a single Josephson junction embedded in a coplanar waveguide structure. Closely related to the unimon qubit, it inherits properties such as high anharmonicity, full protection against low-frequency charge noise, and partial protection against flux noise. By designing such a three-qubit device with Josephson-to-inductive energy ratio above unity and using a leakage-aware encoding scheme for the computational states, we simulate all twelve different controlled-controlled-NOT gates with a mean fidelity of 99.5% with simple sine-squared pulses of comparable length to single-qubit gates. The performance is limited by incoherent errors dominated by dielectric loss. With improvements in noise protection, design, and pulse shaping, the simulations suggest that fidelities approaching 99.99% are within reach. Our results demonstrate the potential of the multiunimon as a highly connected multi-qubit unit for larger superconducting quantum processors.