[论文解读] A Case for Variability-Aware Policies for NISQ-Era Quantum Computers

Swamit Tannu, Moinuddin K. Qureshi|arXiv (Cornell University)|May 25, 2018

Quantum Computing Algorithms and Architecture参考文献 26被引用 49

一句话总结

本论文研究 NISQ 设备上量子比特和链路误差率的变异性，并提出变异感知的量子比特移动和分配策略，通过避免较弱的量子比特/链路来提升可靠性。

ABSTRACT

Recently, IBM, Google, and Intel showcased quantum computers ranging from 49 to 72 qubits. While these systems represent a significant milestone in the advancement of quantum computing, existing and near-term quantum computers are not yet large enough to fully support quantum error-correction. Such systems with few tens to few hundreds of qubits are termed as Noisy Intermediate Scale Quantum computers (NISQ), and these systems can provide benefits for a class of quantum algorithms. In this paper, we study the problems of Qubit-Allocation (mapping of program qubits to machine qubits) and Qubit-Movement(routing qubits from one location to another to perform entanglement). We observe that there exists variation in the error rates of different qubits and links, which can have an impact on the decisions for qubit movement and qubit allocation. We analyze characterization data for the IBM-Q20 quantum computer gathered over 52 days to understand and quantify the variation in the error-rates and find that there is indeed significant variability in the error rates of the qubits and the links connecting them. We define reliability metrics for NISQ computers and show that the device variability has the substantial impact on the overall system reliability. To exploit the variability in error rate, we propose Variation-Aware Qubit Movement (VQM) and Variation-Aware Qubit Allocation (VQA), policies that optimize the movement and allocation of qubits to avoid the weaker qubits and links and guide more operations towards the stronger qubits and links. We show that our Variation-Aware policies improve the reliability of the NISQ system up to 2.5x.

研究动机与目标

• 激发在 NISQ 时代量子计算中考虑量子比特误差率的变异性的必要性。
• 利用在 52 天内收集的 IBM-Q20 数据表征量子比特和链路的误差率变异性。
• 为 NISQ 设备定义可靠性指标，并量化变异性对系统可靠性的影响。
• 提出并评估面向变异性的量子比特移动和量子比特分配策略以提高可靠性。

提出的方法

• 分析 52 天的 IBM-Q20 表征数据以量化量子比特和链路误差率的变异性。
• 定义可靠性指标以评估设备变异性对 NISQ 系统的影响。
• 开发 Variation-Aware Qubit Movement (VQM) 策略，在纠缠操作期间避免较弱的量子比特/链路。
• 开发 Variation-Aware Qubit Allocation (VQA) 策略，将程序量子比特映射到更强的量子比特/链路。
• 通过比较可靠性提升来评估策略，报告最多达到 2.5x 的增益。

实验结果

研究问题

• RQ1 在真实的 IBM-Q20 设备中，随时间变化的量子比特和链路误差率有多大变异？
• RQ2 考虑到这种变异性的移动和分配策略是否能够提升 NISQ 的可靠性？
• RQ3 相比基线策略，应用变异感知策略的潜在可靠性提升是多少？

主要发现

• 在 IBM-Q20 上，52 天内量子比特和链路的误差率存在显著变异性。
• 设备变异性对整体系统可靠性具有显著影响。
• 变异感知的量子比特移动（VQM）和变异感知的量子比特分配（VQA）提高了可靠性，达到最多 2.5x 的提升。