影响超导量子线路性能的噪声和退相干与寄生二能级系统（TLS）的存在是一致的。近年来，体缺陷已被普遍排除为主要来源，并将研究重点放在表面和界面上。尽管有广泛的理论模型和实验努力，这些表面TLS的起源仍然在很大程度上是未知的，使进一步减轻TLS诱导的退相干极具挑战性。在这里，我们使用最近开发的片上电子自旋共振（ESR）技术，使我们能够检测自旋与一个非常低的表面覆盖。我们将这种技术与各种表面处理相结合，专门揭示Al $_2$ O $_3$-几乎所有固态量子器件的支柱上的原生表面自旋的性质。在大量的样品中，我们解决了三个ESR峰与测得的总顺磁自旋密度$n=2.2\times 10^{17}$ m $^{-2}$，这与SQUID中的通量噪声推断的密度相匹配。我们发现，这些峰中的两个起源于物理吸附原子氢出现在表面上作为水解离的副产品。我们认为，第三个峰是由于分子氧的Al $_2$ O $_3$表面上捕获在强路易斯碱缺陷网站，生产带电O $_2^-$。这些结果为研究量子线路中电荷和磁通噪声的来源提供了重要信息。我们的研究结果开辟了一个全新的方法来识别和控制减少固态量子器件中的顺磁噪声源。
英文摘要：
It is universally accepted that noise and decoherence affecting the performance of superconducting quantum circuits are consistent with the presence of spurious two-level systems (TLS). In recent years bulk defects have been generally ruled out as the dominant source, and the search has focused on surfaces and interfaces. Despite a wide range of theoretical models and experimental efforts, the origin of these surface TLS still remains largely unknown, making further mitigation of TLS induced decoherence extremely challenging. Here we use a recently developed on-chip electron spin resonance (ESR) technique that allows us to detect spins with a very low surface coverage. We combine this technique with various surface treatments specifically to reveal the nature of native surface spins on Al$_2$O$_3$ -- the mainstay of almost all solid state quantum devices. On a large number of samples we resolve three ESR peaks with the measured total paramagnetic spin density $n=2.2\times 10^{17}$m$^{-2}$, which matches the density inferred from the flux noise in SQUIDs. We show that two of these peaks originate from physisorbed atomic hydrogen which appears on the surface as a by-product of water dissociation. We suggest that the third peak is due to molecular oxygen on the Al$_2$O$_3$ surface captured at strong Lewis base defect sites, producing charged O$_2^-$. These results provide important information towards the origin of charge and flux noise in quantum circuits. Our findings open up a whole new approach to identification and controlled reduction of paramagnetic sources of noise in solid state quantum devices.
Identification of quantum generative circuits with parallel quantum neural network
School of Computer Science, Northwestern Polytechnical University（西北工业大学计算机学院）；school of cybersecurity, Northwestern Polytechnical University（西北工业大学网络空间安全学院）；School of Information, Central University of Finance and Economics（中央财经大学信息学院）
Error accumulation in dissipative quantum circuits
Universidad Autónoma de Madrid（马德里自治大学）；Instituto Superior Técnico, Universidade de Lisboa（里斯本大学高级理工学院）；University of Stuttgart（斯图加特大学）；Jagiellonian University（雅盖隆大学）；Polish Academy of Sciences（波兰科学院）；OsloMet – Oslo Metropolitan University（奥斯陆都会大学）
MPStab: an hybrid stabilizers tensor-network quantum circuit simulator
University of Trieste（的里雅斯特大学）；Istituto Nazionale di Fisica Nucleare, Trieste Section（意大利国家核物理研究所的里雅斯特分部）；University of Helsinki（赫尔辛基大学）；European Organization for Nuclear Research (CERN)（欧洲核子研究组织（日内瓦））；Chalmers University of Technology（查尔姆斯理工大学）
