Quantum logic with spin qubits crossing the surface code threshold

TLDR

High‑fidelity control of qubits is essential for fault‑tolerant quantum computing, which requires error rates below a ~1 % threshold, and achieving two‑qubit gate fidelities above 99 %—a longstanding goal for semiconductor spin qubits—positions them as scalable platforms. Utilizing this high‑fidelity gate set, we execute the demanding task of calculating molecular ground state energies using a variational quantum eigensolver algorithm. We demonstrate a silicon spin‑based quantum processor with single‑ and two‑qubit gate fidelities exceeding 99.5 %, maintaining >99 % single‑qubit performance even with crosstalk and idling, thereby surpassing the 99 % two‑qubit threshold and establishing semiconductor qubits as a leading high‑fidelity, scalable platform.

Abstract

High-fidelity control of quantum bits is paramount for the reliable execution of quantum algorithms and for achieving fault-tolerance, the ability to correct errors faster than they occur. The central requirement for fault-tolerance is expressed in terms of an error threshold. Whereas the actual threshold depends on many details, a common target is the ~1% error threshold of the well-known surface code. Reaching two-qubit gate fidelities above 99% has been a long-standing major goal for semiconductor spin qubits. These qubits are well positioned for scaling as they can leverage advanced semiconductor technology. Here we report a spin-based quantum processor in silicon with single- and two-qubit gate fidelities all above 99.5%, extracted from gate set tomography. The average single-qubit gate fidelities remain above 99% when including crosstalk and idling errors on the neighboring qubit. Utilizing this high-fidelity gate set, we execute the demanding task of calculating molecular ground state energies using a variational quantum eigensolver algorithm. Now that the 99% barrier for the two-qubit gate fidelity has been surpassed, semiconductor qubits have gained credibility as a leading platform, not only for scaling but also for high-fidelity control.