QuTech, Delft University of Technology, Delft, The Netherlands.
Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft, The Netherlands.
Nature. 2022 Jun;606(7916):884-889. doi: 10.1038/s41586-022-04819-6. Epub 2022 May 5.
Solid-state spin qubits is a promising platform for quantum computation and quantum networks. Recent experiments have demonstrated high-quality control over multi-qubit systems, elementary quantum algorithms and non-fault-tolerant error correction. Large-scale systems will require using error-corrected logical qubits that are operated fault tolerantly, so that reliable computation becomes possible despite noisy operations. Overcoming imperfections in this way remains an important outstanding challenge for quantum science. Here, we demonstrate fault-tolerant operations on a logical qubit using spin qubits in diamond. Our approach is based on the five-qubit code with a recently discovered flag protocol that enables fault tolerance using a total of seven qubits. We encode the logical qubit using a new protocol based on repeated multi-qubit measurements and show that it outperforms non-fault-tolerant encoding schemes. We then fault-tolerantly manipulate the logical qubit through a complete set of single-qubit Clifford gates. Finally, we demonstrate flagged stabilizer measurements with real-time processing of the outcomes. Such measurements are a primitive for fault-tolerant quantum error correction. Although future improvements in fidelity and the number of qubits will be required to suppress logical error rates below the physical error rates, our realization of fault-tolerant protocols on the logical-qubit level is a key step towards quantum information processing based on solid-state spins.
固态自旋量子位是量子计算和量子网络的一个有前途的平台。最近的实验已经证明了对多量子比特系统、基本量子算法和非容错纠错的高质量控制。大规模系统将需要使用容错操作的纠错逻辑量子位，以便即使在噪声操作下也能实现可靠的计算。以这种方式克服不完美仍然是量子科学的一个重要挑战。在这里，我们使用钻石中的自旋量子位演示了逻辑量子位的容错操作。我们的方法基于具有 flag 协议的五量子比特码，该协议使用总共七个量子比特来实现容错。我们使用基于重复多量子比特测量的新协议对逻辑量子位进行编码，并表明它优于非容错编码方案。然后，我们通过一组完整的单量子比特 Clifford 门对逻辑量子位进行容错操作。最后，我们演示了带有实时处理结果的标记稳定器测量。这种测量是容错量子纠错的基本操作。尽管需要提高保真度和量子比特数量，以将逻辑错误率降低到物理错误率以下，但我们在逻辑量子位级别上实现容错协议是基于固态自旋进行量子信息处理的关键一步。
