【Wen/Observer Net Wang Yi】"Chinese research teams have made a major breakthrough in quantum error correction, taking a crucial step forward in the global race to build practical quantum computers."
Hong Kong's South China Morning Post reported on December 26 that the team led by Academician Pan Jianwei of the University of Science and Technology of China successfully crossed the "fault tolerance threshold" of quantum error correction based on the superconducting quantum processor "Zhu Chongzhi 3.2", becoming the first team outside the United States and the second in the world after Google to achieve this key milestone, and also surpassing Google in efficiency.
"Fault tolerance threshold" is the core standard for measuring whether a quantum computer can operate stably at a large scale. For a long time, quantum error correction has faced a problem: the error correction process itself introduces new errors, causing the system to become more unstable as it corrects errors.
The Pan Jianwei team stated that after crossing this threshold, error correction no longer weakens the system's stability but can reduce the overall error rate, i.e., "below the threshold, the more corrections, the more accurate," which is a prerequisite for quantum computing to move from theoretical feasibility to an expandable engineering system.
The report noted that unlike Google's approach of using additional hardware to suppress errors, the Chinese team adopted a microwave-based control method, achieving a key breakthrough without significantly increasing hardware complexity.
In a statement released on the 22nd, the Chinese team pointed out that this approach may be more efficient than Google's solution in building large-scale, fault-tolerant quantum computers.
Superconducting quantum processor "Zhu Chongzhi 3.2" Social Media
Joseph Emerson, a physicist at the University of Waterloo in Canada, wrote in the journal Physics published by the American Physical Society, that qubits are prone to deviate from their set states, silently spreading errors in the system. The Chinese team directly addressed one of the most challenging issues in the field of quantum computing and achieved a "remarkable achievement."
According to the introduction, unlike traditional computers that use simple switch logic, quantum computers operate based on quantum physical laws. Theoretically, they can complete complex tasks that would take traditional computers thousands of years to finish in an extremely short time, such as optimizing complex systems and simulating molecules. However, in reality, quantum computers face serious instability problems. Their basic unit, the qubit, is extremely sensitive to heat, noise, and environmental disturbances, making errors almost inevitable during operation.
To solve this problem, scientists proposed quantum error correction technology, which maintains computational reliability by dispersing information across multiple qubits and repeatedly detecting errors. However, this approach also brings a paradox: each additional qubit or each detection introduces new sources of error. Years of practice have shown that before reaching specific conditions, error correction often backfires.
Therefore, researchers focused on a critical point called the "fault tolerance threshold." Below the threshold, error correction creates more errors than it eliminates; once it exceeds the threshold, error correction brings a net benefit, and the larger the system, the more stable it becomes.
According to the South China Morning Post, both China and the United States had invested in surface code research early on. This scheme is one of the most mature and widely studied quantum error correction schemes. In 2022, Pan Jianwei's team used the "Zhu Chongzhi 2" superconducting quantum processor to realize a surface code logical qubit with a code distance of 3, first verifying the feasibility of the surface code scheme.
The following year, Google advanced this technology to a surface code error correction with a code distance of 5, but due to the relatively high error levels of physical qubits at the time, neither of these works truly broke through the error correction threshold.
In February of this year, Google achieved a breakthrough with its "Willow" processor by using a DC pulse-based quantum state leakage suppression method, achieving a logical bit below the threshold on a surface code with a code distance of 7. However, this method imposes strict constraints on the chip architecture of the quantum processor and requires more complex wiring in ultra-low temperature environments, posing challenges for system expansion.
In the latest study, the team from the University of Science and Technology of China took a different approach. Based on the 107-qubit "Zhu Chongzhi 3.2" quantum processor, they proposed a full microwave scheme to suppress leakage errors, rather than adding extra hardware controls. Combined with surface code error correction technology, the Chinese researchers also built a logical qubit with a code distance of 7.
Experimental results showed that as the system size increased, the overall error rate decreased instead of increasing, with an error suppression factor of 1.4, proving that the system was operating below the error correction threshold and successfully achieving the goal of "the more corrections, the more accurate."
Moreover, the Pan Jianwei team pointed out that the full microwave quantum state leakage suppression architecture has significant advantages in hardware efficiency and scalability compared to Google's technical route. Since microwave signals can be reused, multiple signals can be transmitted along the same wire, and this method has the potential to significantly reduce wiring complexity and hardware burden, which are two major bottlenecks restricting the scaling of quantum processors.
The team believes that overall, this achievement points to a more flexible and scalable technical path, which could help push quantum computers toward tens of thousands or even millions of qubits.
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Original: toutiao.com/article/7588182001107157504/
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