Noisy Intermediate-Scale Quantum Computing (NISQ) has dominated headlines in recent years, with the longer-term vision of Fault-Tolerant Quantum Computation (FTQC) offering significant potential albeit at currently intractable resource costs and quantum error correction (QEC) overheads. For problems of interest, FTQC will require millions of physical qubits with long coherence times, high-fidelity gates, and compact sizes to surpass classical systems. Just as heterogeneous specialization has offered scaling benefits in classical computing, it is likewise gaining interest in FTQC. However, systematic use of heterogeneity in either hardware or software elements of FTQC systems remains a serious challenge due to the vast design space and variable physical constraints. This paper meets the challenge of making heterogeneous FTQC design practical by introducing HetArch, a toolbox for designing heterogeneous quantum systems, and using it to explore heterogeneous design scenarios. Using a hierarchical approach, we successively break quantum algorithms into smaller operations (akin to classical application kernels), thus greatly simplifying the design space and resulting tradeoffs. Specializing to superconducting systems, we then design optimized heterogeneous hardware composed of varied superconducting devices, abstracting physical constraints into design rules that enable devices to be assembled into standard cells optimized for specific operations. Finally, we provide a heterogeneous design space exploration framework which reduces the simulation burden by a factor of 10^4 or more and allows us to characterize optimal design points. We use these techniques to design superconducting quantum modules for entanglement distillation, error correction, and code teleportation, reducing error rates by 2.6x, 10.7x, and 3.0x compared to homogeneous systems.

翻译：噪声中等规模量子计算（NISQ）近年来占据头条新闻，而容错量子计算（FTQC）的长期愿景虽具有巨大潜力，但目前面临难以承受的资源成本与量子纠错（QEC）开销。对于有价值的问题，FTQC需要数百万个具有长相干时间、高保真度门和紧凑尺寸的物理量子比特才能超越经典系统。正如异质化集成技术为经典计算带来扩展优势一样，它同样在FTQC领域引起关注。然而，由于设计空间庞大且物理约束多变，在FTQC系统的硬件或软件元素中系统性地应用异质性仍是一项严峻挑战。本文通过引入异质量子系统设计工具箱HetArch，并利用其探索异质设计场景，从而应对使异质FTQC设计实用化的挑战。采用分层方法，我们逐步将量子算法分解为更小的操作（类似于经典应用内核），从而大幅简化设计空间及其折衷权衡。针对超导系统，我们进一步设计了由多样化超导器件组成的优化异质硬件，将物理约束抽象为设计规则，使器件能组装成针对特定操作优化的标准单元。最后，我们提供一个异质设计空间探索框架，可将仿真负担降低10^4倍以上，并能够表征最优设计点。利用这些技术，我们设计了用于纠缠蒸馏、纠错和代码隐形传态的超导量子模块，与同质系统相比，错误率分别降低了2.6倍、10.7倍和3.0倍。