Researchers at the University of Science and Technology of China (USTC) have demonstrated fault-tolerant quantum error correction (QEC) below the surface code threshold using the 107-qubit Zuchongzhi 3.2 superconducting processor. Published as an Editors’ Suggestion in Physical Review Letters on December 22, 2025, the study confirms that logical error rates suppress exponentially as code size increases, marking the first time a research group outside the United States has reached this “break-even” milestone. The team achieved a logical error suppression factor of Λ = 1.40(6) using a distance-7 (d=7) surface code, proving that the system has moved beyond the regime where error correction introduces more noise than it removes.
The technical breakthrough centers on a novel all-microwave leakage suppression architecture that addresses long-lived, correlated errors caused by quantum information escaping the computational subspace. Unlike previous methods that rely on hardware-intensive direct-current pulses, the USTC approach integrates a hardware-efficient leakage reduction unit with a fast, unconditional reset for ancilla qubits using carefully timed microwave signals. This architecture suppressed the average leakage population by a factor of 72 to 6.4(5) × 10-4 after 40 QEC cycles. Additionally, the Zuchongzhi 3.2 processor demonstrated high-fidelity performance with a readout error rate of only 0.95% within a 300-nanosecond window.
This all-microwave pathway offers a significant scalability advantage over hardware-heavy alternatives by reducing wiring density and complexity inside the dilution refrigerator. By demonstrating that leakage—one of the most stubborn hurdles for surface codes—can be mitigated through the existing microwave control layer, the researchers have established a viable foundation for scaling superconducting systems toward millions of qubits. This milestone follows the team’s earlier Zuchongzhi 3.0 record in March 2025 and confirms that the technical gap in fault-tolerant hardware between China and Western leaders like Google has narrowed to parity.
Read the official research paper in Physical Review Letters here, the report from Global Times here, and the summary from Bastille Post here.
December 30, 2025
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