微观材料缺陷中的库仑阻塞作为固态量子电路中退相干和噪声的来源
Coulomb blockade in microscopic material defects as a source of decoherence and noise in solid-state quantum circuits
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中文总结 AI 辅助
研究固态量子器件中退相干问题，通过扫描门显微镜发现源于金属颗粒库仑阻塞和微波驱动电荷隧穿的新退相干机制，其与TLS缺陷不同且常被传统技术误判，消除金属颗粒可抑制此机制提升器件性能。
中文摘要 AI 辅助
固态量子器件的一个关键限制源于其制造材料：不受控制的表面、界面和结构缺陷会引入大量损耗和退相干源。尽管进行了大量努力，但将这些退相干机制与其微观材料起源联系起来（这对制定有效的缓解策略至关重要）仍然是一个突出的挑战，阻碍了相干性的提高。在此，通过对超导电路进行扫描门显微镜观察，我们发现了一种先前未被认识的退相干机制，它源于金属颗粒中的库仑阻塞和微波驱动的电荷隧穿。通过对不同器件中的多个缺陷进行表征，我们发现这些缺陷与两能级系统（TLS）缺陷一样普遍且对器件性能有害，但源于根本不同的物理机制。重要的是，传统表征技术会将这种损耗误归因于其他与微波功率无关的过程。我们的观察结果揭示了超导电路中广泛存在的退相干源，挑战了相干寿命主要受TLS缺陷限制的主流范式。在制造过程中消除金属颗粒为抑制这种机制提供了一条明确且实用的途径，为提高基于微波的固态量子器件的相干性和降低噪声提供了一条途径。
英文摘要
A critical limitation of solid-state quantum devices arises from the materials from which they are fabricated: uncontrolled surfaces, interfaces, and structural imperfections introduce numerous sources of loss and decoherence. Despite extensive efforts, linking these decoherence mechanisms to their microscopic material origins -- essential for developing effective mitigation strategies -- remains an outstanding challenge that has slowed coherence improvements. Here, using scanning gate microscopy on live superconducting circuits we identify a previously unrecognised decoherence mechanism originating from Coulomb blockade and microwave-driven charge tunnelling in metallic grains. Such grains are ubiquitous in thin-film devices fabricated by standard lithography processes. By characterising multiple defects across different devices, we find such defects to be as common and as debilitating to device performance as two-level system (TLS) defects, while originating from a fundamentally different physical mechanism. Importantly, conventional characterisation techniques would misattribute this loss to other, microwave power-independent processes. Our observations thus reveal a widespread source of decoherence in superconducting circuits, challenging the prevailing paradigm that coherence lifetimes are primarily limited by TLS defects. Eliminating metallic grains during fabrication provides a clear and practical route to suppress this mechanism, offering a pathway towards improved coherence and reduced noise in microwave-based solid-state quantum devices.
