强各向异性非克莱默斯电子自旋作为角涨落的量子相干探针

中文摘要 AI 辅助

强各向异性非克莱默斯稀土离子兼具巨纵向g因子与时间反演对称要求下的消失横向分量，这种组合使其自旋跃迁对所施加磁场的取向极为敏感。我们表明这种敏感性具有双重属性：它既是一种被忽视的退相干通道，也是基于自旋相干性的角探针的基础。利用X波段脉冲电子顺磁共振，我们首次测量了原生掺杂CaWO₄晶体（掺杂浓度15ppb）中Tb³⁺的量子相干性，并绘制了 Hahn回波相干时间T₂随温度（2至10K）和谐振场（10³至10⁴G）的变化关系。结合自旋-晶格弛豫、瞬时扩散和所有独立量化杂质引起的谱扩散的无参数模型，在低温下对T₂的估计值高出一个数量级，且错误预测了T₂的场依赖关系，与观测到的T₂随B_r单调下降的结果不一致。包含晶体轴动力学角涨落的双参数扩展模型，可重现多个装置和实验室的完整数据集。两个仅装置机械配置不同的受控实验，确定了主导贡献的机械起源。该双参数扩展对应于约2.5kHz处来自全局外部振动的角振幅噪声谱密度，整体量级为36n°/√Hz（根据装置精确机械配置，范围为10至66n°/√Hz），加上被认为来自局部声子驱动角抖动的温度相关贡献。它识别并强调了对任何各向异性固态自旋系统都具有实际意义的退相干途径。

英文摘要

Strongly anisotropic non-Kramers rare-earth ions combine giant longitudinal g-factors with a vanishing transverse component imposed by time-reversal symmetry, a combination that makes their spin transitions exquisitely sensitive to the orientation of the applied magnetic field. We show that this sensitivity carries a dual identity: it is simultaneously an overlooked decoherence channel and the basis for a spin-coherence-based angular probe. Using pulsed electron paramagnetic resonance at X-band, we report the first measurements of the quantum coherence of Tb$^{3+}$ in a native-doped CaWO$_4$ crystal (15 ppb) and map the Hahn-echo coherence time $T_2$ as a function of temperature (2 to 10 K) and resonant field ($10^3$ to $10^4$ G). A parameter-free model combining spin-lattice relaxation, instantaneous diffusion and spectral diffusion from all independently quantified impurities overestimates $T_2$ by an order of magnitude at low temperature and wrongly predicts the field dependence of $T_2$, inconsistent with the observed monotonic decrease of $T_2$ with $B_r$. A two-parameter extension, including dynamical angular fluctuations of the crystal axis, reproduces the full dataset across multiple setups and laboratories. Two controlled experiments nominally identical except for different mechanical configuration of the setup establish the mechanical origin of the dominant contribution. The two-parameter extension corresponds to an angular amplitude noise spectral density of overall order 36 n°/$\sqrt{Hz}$ from global external vibrations (ranging from 10 to 66 n°/$\sqrt{Hz}$ depending on the exact setup mechanical configuration) estimated at $\sim$ 2.5 kHz plus a temperature-dependent contribution assumed to come from local phonon-driven angular jitter. It identifies and highlights a decoherence pathway of practical relevance to any anisotropic solid-state spin system.

发表机构

• CNRS, Aix-Marseille Université, Université de Toulon, IM2NP（法国国家科学研究中心、艾克斯-马赛大学、土伦大学、IM2NP）
• Institut de Chimie de Strasbourg, UMR 7177, CNRS-Université de Strasbourg（斯特拉斯堡化学研究所、UMR 7177、法国国家科学研究中心-斯特拉斯堡大学）
• Quantronics group, Service de Physique de l’État Condensé (CNRS, UMR 3680), IRAMIS, CEA-Saclay, Université Paris-Saclay（量子电子学小组、凝聚态物理服务处（法国国家科学研究中心、UMR 3680）、IRAMIS、巴黎萨克雷原子能委员会、巴黎萨克雷大学）
• Chimie ParisTech, PSL University, CNRS, Institut de Recherche de Chimie Paris（巴黎高等师范学院化学学院、PSL大学、法国国家科学研究中心、巴黎化学研究院）

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