【arXiv导读】并非所有的量子比特都被制备得相同（Not All Qubits Are Created Equal: A Case for Variability-Aware Policies for NISQ-Era Quantum Computers) [arXiv:1805.10224]

题目：

Not All Qubits Are Created Equal: A Case for Variability-Aware Policies for NISQ-Era Quantum Computers

作者：Swamit S. Tannu, Moinuddin K.Qureshi
单位：Georgia Institute of Technology

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摘要：
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 significant 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 improves the reliability of the NISQ system upto 2.5x.

简评：

现有的和近期的量子计算机虽然足够被称为量子计算的里程碑，但其实用价值依然有限。这种限制一是源于他门拥有的量子比特数太少（通常数十到数百量子比特），二是源于系统噪声太大，工作极不稳定；从而直接导致了计算机必须具备的纠错过程（量子计算机的情形下即量子纠错）无法实现。这篇文章主要研究了量子比特分配（Qubit-Allocation，对应于经典计算机的比特分配）和量子比特移动（Qubit-Movement，一种纠缠制备过程）的问题。这篇文章的作者分析了IBM-Q20量子计算机52天的工作数据，发现不同的量子比特和不同的量子比特间的连接（link）拥有不同的错误率。因此，他们验证了对于现在的量子计算机内部处于不同功能的量子比特，其工作状态也会相差很大这一事实。在此基础上，这篇文章也提出了一套改善量子比特分配和量子比特移动在量子计算机上运行效果的办法。