Twisted superconducting quantum diodes: Towards anharmonicity and high fidelity

As quantum technologies advance, a fundamental challenge is mitigating noise and backscattering in superconducting circuits to achieve scalable, high-fidelity operations. Conventional superconducting components lack directionality, causing energy loss and decoherence. Superconducting diodes, that allow dissipationless current in one direction and resistive flow in the other, offer a potential remedy, yet their efficiency and quantum integration remain limited. Here, we realize a quantum diode in twisted NbSe2 bilayers under in-plane and out-of-plane magnetic fields. A mere 1 degree twist yields an efficiency enhancement over pristine devices, reaching 27.6 percent. Quantum simulations reveal that this intermediate efficiency, well below 100 percent ideal, is both experimentally practical and optimal for preserving qubit anharmonicity and stabilizing two-level systems. These findings show that maximal rectification is not always beneficial for quantum information, establishing a new principle for designing the fundamental properties of twisted superconductors towards low-power, high-fidelity quantum circuits.