Superconducting quantum circuits at the surface code threshold for fault tolerance
Superconducting quantum circuits at the surface code threshold for fault tolerance
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DOI：
10.1038/nature13171
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发表时间：
2014-04-24
期刊：
影响因子：
64.8
通讯作者：
Martinis, John M.
中科院分区：
文献类型：
--
作者：
Barends, R.;Kelly, J.;Martinis, John M.
量子计算机可以解决一些困难的问题，例如素数分解（1，2），数据库搜索（3，4）和量子模拟（5），但代价是需要保护脆弱的量子态不受错误的影响。量子纠错（6）通过量子纠缠在许多物理量子比特（qubit）之间分配逻辑状态来提供这种保护。在这方面，超导性是一种有用的现象，因为它允许构建大型量子电路，并与微制造兼容。对于超导量子比特，量子计算的表面编码方法（7）是纠错的自然选择，因为它只使用最近邻耦合和快速循环的纠缠门。栅极保真度要求不高：每步保真度阈值仅为99%。在这里，我们展示了超导多量子位处理器中的一组通用逻辑门，实现了99.92%的平均单量子比特门保真度和高达99.4%的双量子比特门保真度。这将约瑟夫森量子计算置于错误之中-表面码纠错的容限阈值。我们的量子处理器是迈向表面代码的第一步，使用五个量子位以线性阵列排列，具有最近邻耦合。作为进一步的演示，我们使用完整的电路和全套门构造了一个五量子比特的Greenberger-Horne-Zeilinger态（8，9）。结果表明，约瑟夫森量子计算是一种高保真技术，具有扩展到大规模容错量子电路的清晰路径。
A quantum computer can solve hard problems, such as prime factoring(1,2), database searching(3,4) and quantum simulation(5), at the cost of needing to protect fragile quantum states from error. Quantum error correction(6) provides this protection by distributing a logical state among many physical quantum bits (qubits) by means of quantum entanglement. Superconductivity is a useful phenomenon in this regard, because it allows the construction of large quantum circuits and is compatible with microfabrication. For superconducting qubits, the surface code approach to quantum computing(7) is a natural choice for error correction, because it uses only nearest-neighbour coupling and rapidly cycled entangling gates. The gate fidelity requirements are modest: the per-step fidelity threshold is only about 99 per cent. Here we demonstrate a universal set of logic gates in a superconducting multi-qubit processor, achieving an average single-qubit gate fidelity of 99.92 per cent and a two-qubit gate fidelity of up to 99.4 per cent. This places Josephson quantum computing at the fault-tolerance threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbour coupling. As a further demonstration, we construct a five-qubit Greenberger-Horne-Zeilinger state(8,9) using the complete circuit and full set of gates. The results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.