The spin degree of freedom of an electron or a nucleus is one of the most basic properties of nature and functions as an excellent qubit, as it provides a natural two-level system that is insensitive to electric fields, leading to long quantum coherence times. This coherence survives when the spin is isolated and controlled within nanometer-scale, lithographically fabricated semiconductor devices, enabling the existing microelectronics industry to help advance spin qubits into a scalable technology. Driven by the burgeoning field of quantum information science, worldwide efforts have developed semiconductor spin qubits to the point where quantum state preparation, multiqubit coherent control, and single-shot quantum measurement are now routine. The small size, high density, long coherence times, and available industrial infrastructure of these qubits provide a highly competitive candidate for scalable solid-state quantum information processing. Here the physics of semiconductor spin qubits is reviewed, with a focus not only on the early achievements of spin initialization, control, and readout in GaAs quantum dots but also on recent advances in Si and Ge spin qubits, including improved charge control and readout, coupling to other quantum degrees of freedom, and scaling to larger system sizes. First introduced are the four major types of spin qubits: single spin qubits, donor spin qubits, singlet triplet spin qubits, and exchange-only spin qubits. The mesoscopic physics of quantum dots, including single-electron charging, valleys, and spin-orbit coupling, are then reviewed. Next a comprehensive overview of the physics of exchange interactions is given, a crucial resource for single- and two-qubit control in spin qubits. The bulk of the review is centered on the presentation of results from each major spin-qubit type, the present limits of fidelity, and an overview of alternative spin-qubit platforms. A physical description of the impact of noise on semiconductor spin qubits, aided in large part by an introduction to the filter-function formalism, is then given. Last, recent efforts to hybridize spin qubits with superconducting systems, including charge-photon coupling, spin-photon coupling, and long-range cavity-mediated spin-spin interactions, are reviewed. Cavity-based readout approaches are also discussed. The review is intended to give an appreciation for the future prospects of semiconductor spin qubits while highlighting the key advances in mesoscopic physics over the past two decades that underlie the operation of modern quantum-dot and donor spin qubits.

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半导体自旋量子位

电子或原子核的自旋自由度是自然界最基本的属性之一，可以作为优秀的量子位，因为它提供了对电场不敏感的自然两能级系统，从而导致较长的量子相干时间。当自旋在纳米级光刻制造的半导体器件中被隔离和控制时，这种相干性得以存在，从而使现有的微电子行业能够帮助将自旋量子位推进为可扩展的技术。在新兴的量子信息科学领域的推动下，全球范围内的努力已经将半导体自旋量子位开发到了量子态制备、多量子位相干控制和单次量子测量现已成为常规的程度。这些量子位的小尺寸、高密度、长相干时间和可用的工业基础设施为可扩展的固态量子信息处理提供了极具竞争力的候选者。这里回顾了半导体自旋量子位的物理学，不仅关注砷化镓量子点中自旋初始化、控制和读出的早期成就，还关注硅和锗自旋量子位的最新进展，包括改进的电荷控制和读出，耦合到其他量子自由度，并扩展到更大的系统尺寸。首先介绍四种主要类型的自旋量子位：单自旋量子位、供体自旋量子位、单重态三重态自旋量子位和仅交换自旋量子位。然后回顾了量子点的介观物理，包括单电子充电、谷和自旋轨道耦合。接下来，对交换相互作用的物理原理进行了全面的概述，这是自旋量子位中单量子位和两个量子位控制的重要资源。审查的大部分内容集中在每种主要自旋量子位类型的结果的呈现、当前保真度的限制以及替代自旋量子位平台的概述。然后给出了噪声对半导体自旋量子位的影响的物理描述，在很大程度上通过引入滤波器函数形式主义来辅助。最后，回顾了最近自旋量子位与超导系统杂交的努力，包括电荷-光子耦合、自旋-光子耦合和长程腔介导的自旋-自旋相互作用。还讨论了基于腔的读出方法。该评论旨在评估半导体自旋量子位的未来前景，同时强调过去二十年介观物理学的关键进展，这些进展是现代量子点和施主自旋量子位运行的基础。