We review the problem of spin decoherence of magnetic atoms deposited on a surface. Recent breakthroughs in scanning tunnelling microscopy (STM) make it possible to probe the spin dynamics of individual atoms, either isolated or integrated in nanoengineered spin structures. Transport pump and probe techniques with spin polarized tips permit measuring the spin relaxation time $T_1$, while novel demonstration of electrically driven STM single spin resonance has provided a direct measurement of the spin decoherence time $T_2$ of an individual magnetic adatom. Here we address the problem of spin decoherence from the theoretical point of view. First we provide a short general overview of decoherence in open quantum systems and we discuss with some detail ambiguities that arise in the case of degenerate spectra, relevant for magnetic atoms. Second, we address the physical mechanisms that allows probing the spin coherence of magnetic atoms on surfaces. Third, we discuss the main spin decoherence mechanisms at work on a surface, most notably, Kondo interaction, but also spin-phonon coupling and dephasing by Johnson noise. Finally, we propose some schemes to engineer spin decoherence.

中文翻译：

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表面磁性原子的自旋退相干

我们回顾了沉积在表面上的磁性原子的自旋退相干问题。扫描隧道显微镜 (STM) 的最新突破使得探测单个原子的自旋动力学成为可能，无论是孤立的还是集成在纳米工程自旋结构中。具有自旋极化尖端的传输泵和探针技术允许测量自旋弛豫时间 $T_1$，而电驱动 STM 单自旋共振的新颖演示提供了对单个磁吸附原子的自旋退相干时间 $T_2$ 的直接测量。在这里，我们从理论的角度解决自旋退相干问题。首先，我们简要概述了开放量子系统中的退相干性，并讨论了与磁原子相关的简并光谱情况下出现的一些细节模糊性。第二，我们解决了允许探测表面磁性原子自旋相干性的物理机制。第三，我们讨论了在表面上工作的主要自旋退相干机制，最显着的是近藤相互作用，以及约翰逊噪声引起的自旋声子耦合和去相。最后，我们提出了一些设计自旋退相干的方案。