Quantum Error Correction Threshold Achievement

According to the latest research progress, a team from the University of Science and Technology of China (USTC) achieved quantum error correction below the threshold in the surface code regime for the first time at the end of 2025. The core of this breakthrough is not a single specific numerical value, but a critical technical state: the overall error rate of the system's physical qubits has dropped below the theoretical limit required for the surface code scheme to provide positive error correction, realizing the state of "error suppression."

Research Details and Technical Comparison

For clarity, here is a comparison of the key information between the Chinese team (USTC) and Google in achieving this milestone:

Research Aspect	University of Science and Technology of China (USTC)	Google
Research Team	Jianwei Pan, Xiaobo Zhu, Chengzhi Peng, Fusheng Chen, et al.	Google Quantum AI Lab
Publication Date	December 2025	Early 2025 (Nature paper)
Experimental Platform	Zuchongzhi 3.2 (107 qubits)	Willow (105 qubits)
Error-Correcting Code	Distance-7 surface code	Distance-7 surface code
Key Metric	Error Suppression Factor: 1.40	Error Suppression Factor: 2.14
Technical Approach	All-microwave quantum state leakage suppression architecture	DC-pulse quantum state leakage suppression method
Core Advantage	Fewer hardware constraints, lower wiring complexity, greater potential for scalability	Higher error suppression factor

Note on Error Suppression Factor (Λ): An Error Suppression Factor (Λ) greater than 1 means the logical error rate decreases exponentially as the code size increases. This is direct experimental evidence that the system is operating below the error correction threshold.

Understanding the "Error Correction Threshold"

Simply put, the error correction threshold is like a "passing line":

• Physical qubit error rate above the threshold: The additional errors introduced by the correction process itself outweigh the benefits, leading to "more errors with correction."

• Physical qubit error rate below the threshold: Error correction yields a net positive benefit. The system enters the ideal "error suppression" state, where a logical qubit can be more stable than any of its constituent physical qubits.

Key Differences in Technical Approaches

While both teams achieved this milestone, their technical paths differ significantly:

China's "All-Microwave" Path

Uses microwave signals for unified control, reuses existing hardware, and is naturally suited for multiplexing. This greatly reduces wiring complexity and hardware overhead in the extreme low-temperature environment required for large-scale expansion.

Google's "DC-Pulse" Path

Suppresses errors by applying DC pulses, which is effective but imposes specific constraints on chip design (e.g., qubit connectivity) and incurs greater hardware resource overhead during large-scale scaling.

In summary, while Google's solution currently demonstrates a better specific metric (error suppression factor), the Chinese team's approach is architecturally simpler and is considered to have greater potential for scalability on the path toward million-qubit-scale quantum computers.

In short, the USTC team is the second in the world, after Google, to achieve sub-threshold quantum error correction in the surface code regime. This breakthrough is a critical watershed that quantum computing must cross to move from laboratory prototypes to practical applications, and the proposed new architecture provides an important technical option for future large-scale scaling.

If you are interested in the basic principles of quantum error correction or why surface codes are the current mainstream approach, further explanations are available.