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Fault-Tolerant Operation of Bosonic Qubits with Discrete-Variable Ancillae
Physical Review X ( IF 11.6 ) Pub Date : 2024-07-30 , DOI: 10.1103/physrevx.14.031016
Qian Xu 1 , Pei Zeng 1 , Daohong Xu 1 , Liang Jiang 1
Affiliation  

Fault-tolerant quantum computation with bosonic qubits often necessitates the use of noisy discrete-variable ancillae. In this work, we establish a comprehensive and practical fault-tolerance framework for such a hybrid system and synthesize it with fault-tolerant protocols by combining bosonic quantum error correction (QEC) and advanced quantum control techniques. We introduce essential building blocks of error-corrected gadgets by leveraging ancilla-assisted bosonic operations using a generalized variant of path-independent quantum control. Using these building blocks, we construct a universal set of error-corrected gadgets that tolerate a single-photon loss and an arbitrary ancilla fault for four-legged cat qubits. Notably, our construction requires only dispersive coupling between bosonic modes and ancillae, as well as beam-splitter coupling between bosonic modes, both of which have been experimentally demonstrated with strong strengths and high accuracy. Moreover, each error-corrected bosonic qubit is comprised of only a single bosonic mode and a three-level ancilla, featuring the hardware efficiency of bosonic QEC in the full fault-tolerant setting. We numerically demonstrate the feasibility of our schemes using current experimental parameters in the circuit-QED platform. Finally, we present a hardware-efficient architecture for fault-tolerant quantum computing by concatenating the four-legged cat qubits with an outer qubit code utilizing only beam-splitter couplings. Our estimates suggest that the overall noise threshold can be reached using existing hardware. These developed fault-tolerant schemes extend beyond their applicability to four-legged cat qubits and can be adapted for other rotation-symmetrical codes, offering a promising avenue toward scalable and robust quantum computation with bosonic qubits.

中文翻译:


具有离散变量辅助的玻色子量子比特的容错操作



使用玻色子量子比特的容错量子计算通常需要使用嘈杂的离散变量辅助设备。在这项工作中,我们为这种混合系统建立了一个全面而实用的容错框架,并通过结合玻色子量子纠错 (QEC) 和先进的量子控制技术将其与容错协议进行综合。我们通过使用与路径无关的量子控制的广义变体来利用辅助玻色子操作,引入了纠错小工具的基本构建块。使用这些构建块,我们构建了一组通用的纠错小工具,这些小工具可以容忍四足猫量子比特的单光子损失和任意辅助故障。值得注意的是,我们的结构只需要玻色子模式和辅助材料之间的色散耦合,以及玻色子模式之间的分束器耦合,这两者都已被实验证明具有很强的强度和高精度。此外,每个纠错的玻色子量子比特仅由一个玻色子模式和一个三级辅助器件组成,在完全容错设置中具有玻色子 QEC 的硬件效率。我们使用电路 QED 平台中的当前实验参数以数字方式证明了我们方案的可行性。最后,我们提出了一种用于容错量子计算的硬件高效架构,方法是将四足猫量子比特与外部量子比特代码连接起来,仅利用分束器耦合。我们的估计表明,使用现有硬件可以达到总体噪声阈值。 这些开发的容错方案超出了其对四足猫量子比特的适用性,并且可以适用于其他旋转对称代码,为使用玻色子量子比特进行可扩展和稳健的量子计算提供了一条有前途的途径。
更新日期:2024-07-30
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