[论文解读] An Efficient Methodology for Mapping Quantum Circuits to the IBM QX Architectures

Alwin Zulehner, Alexandru Paler+1 more|arXiv (Cornell University)|Dec 13, 2017

Quantum Computing Algorithms and Architecture被引用 7

一句话总结

本文提出了一种基于A*的高效方法，用于将量子电路映射到IBM QX架构，该方法利用基于深度的分割、前瞻优化和动态量子比特映射初始化。与IBM的原生QISKit映射相比，该方法平均将门数减少了27.5%，并在秒级时间内完成映射，而IBM在60个案例中的10个出现超时。

ABSTRACT

In the past years, quantum computers more and more have evolved from an academic idea to an upcoming reality. IBM's project IBM Q can be seen as evidence of this progress. Launched in March 2017 with the goal to provide access to quantum computers for a broad audience, this allowed users to conduct quantum experiments on a 5-qubit and, since June 2017, also on a 16-qubit quantum computer (called IBM QX2 and IBM QX3, respectively). Revised versions of these 5-qubit and 16-qubit quantum computers (named IBM QX4 and IBM QX5, respectively) are available since September 2017. In order to use these, the desired quantum functionality (e.g. provided in terms of a quantum circuit) has to be properly mapped so that the underlying physical constraints are satisfied - a complex task. This demands solutions to automatically and efficiently conduct this mapping process. In this paper, we propose a methodology which addresses this problem, i.e. maps the given quantum functionality to a realization which satisfies all constraints given by the architecture and, at the same time, keeps the overhead in terms of additionally required quantum gates minimal. The proposed methodology is generic, can easily be configured for similar future architectures, and is fully integrated into IBM's SDK. Experimental evaluations show that the proposed approach clearly outperforms IBM's own mapping solution. In fact, for many quantum circuits, the proposed approach determines a mapping to the IBM architecture within minutes, while IBM's solution suffers from long runtimes and runs into a timeout of 1 hour in several cases. As an additional benefit, the proposed approach yields mapped circuits with smaller costs (i.e. fewer additional gates are required). All implementations of the proposed methodology is publicly available at http://iic.jku.at/eda/research/ibm_qx_mapping.

研究动机与目标

• 为解决在物理约束（如受限的CNOT门连通性）下将量子电路映射到IBM QX架构的挑战。
• 减少映射过程中引入的附加门（如SWAP门）的开销，这些门会降低电路保真度和运行时间。
• 开发一种可扩展、通用且高效的映射解决方案，其在速度和电路质量方面优于现有工具（如IBM的QISKit）。
• 将所提出的方法集成到IBM的QISKit SDK中，以实现真实性能评估并促进广泛采用。

提出的方法

• 该方法采用基于深度的分割，将量子电路划分为可管理的片段，以减少映射的搜索空间。
• 使用带有自定义启发式函数的A*搜索算法，高效探索有效量子比特映射，同时最小化附加门的数量。
• 采用前瞻机制预测未来约束，并在搜索初期引导搜索朝向更有希望的映射方向。
• 初始量子比特映射并非在开始时固定，而是在搜索过程中动态确定，从而提升解的质量和适应性。
• 该方法与IBM的QISKit SDK无缝集成，可与IBM原生映射及后续优化进行一致比较。
• 该框架具有通用性，可轻松适配未来具有类似连通性约束的IBM QX类架构。

实验结果

研究问题

• RQ1 系统性搜索方法是否能在门数和运行时间方面优于随机或基于启发式的映射方法？
• RQ2 动态量子比特映射初始化如何影响量子电路映射的质量和效率？
• RQ3 基于深度的分割和前瞻技术在多大程度上能减少搜索空间并提升映射可扩展性？
• RQ4 所提出的方法能否在保持兼容性和性能的前提下，有效集成到现有量子软件栈（如QISKit）中？

主要发现

• 所提出的方法在秒级时间内将全部60个基准电路成功映射到IBM QX5，而IBM的QISKit解决方案在10个案例中因超时一小时未完成。
• 与IBM的平均结果相比，该方法平均将门数减少了27.5%；与IBM的最佳结果（最小值）相比，减少了24.0%。
• 与IBM的平均结果相比，该方法在电路深度上平均减少了22.0%；与IBM的最佳结果相比，减少了18.3%。
• 该方法展现出显著的速度提升，运行时间始终低于一分钟，而IBM的解决方案经常超过一小时的超时限制。
• 与QISKit的集成确保了公平比较，证实性能提升源于映射逻辑本身，而非后期处理优化。
• 该方法具有通用性，可复用于未来具有类似连通性约束的IBM QX类架构。