AI 中文总结
研究人员通过Redfield弛豫理论明确脂肪链长寿命核自旋态与相干性的起源，构建通用框架实现非手性分子中多亚甲基链的相关态与相干性构建，为核自旋序保存及相关应用奠定基础。
AI 中文摘要
脂肪链中的离域长寿命态（LLSs）与集体零量子长寿命相干性（LLCs）为保存核自旋序提供了极具前景的途径，其寿命分别超过常规的$T_1$和$T_2$弛豫时间。这类长寿命特性使其在多个应用领域颇具吸引力，包括超极化存储、基于与靶蛋白结合后长寿命损失的配体观测药物筛选，以及利用多体自旋系统集体特性的量子信息处理。尽管LLSs与LLCs已在亚甲基网络中被实验观测到，但它们在任意长度链中的起源与通用结构仍不明确。本文中，我们表明这些受弛豫保护的模式直接源自Redfield弛豫理论。具体而言，我们构建了长寿命子空间，即与主导的成对偶极-偶极弛豫机制相关的弛豫超算符的零本征值子空间。该长寿命子空间包含$2^N-1$个独立的非平凡算符（排除单位算符），其中$N>1$为链中$-\text{CH}_2-$基团的数量。在非手性分子中，全局成对置换宇称的守恒将实验可及的算符数量限制为至多$2^N-2$个；而在手性分子中，该宇称不守恒，可及的长寿命算符数量可达$2^N-1$个。我们进一步开发了在非手性分子中构建含任意数量$-\text{CH}_2-$基团的脂肪链中LLSs与LLCs的通用框架，并针对$N=2、3、4$个亚甲基的链明确示例了该方法。
英文摘要
Delocalized long-lived states (LLSs) and collective zero-quantum long-lived coherences (LLCs) in aliphatic chains provide a promising route for preserving nuclear spin order with lifetimes that exceed the conventional $T_1$ and $T_2$ relaxation times, respectively. Their extended lifetimes make them attractive for applications including hyperpolarization storage, ligand-observed drug screening based on the loss of longevity upon binding to a target protein, and quantum information processing exploiting the collective properties of many-body spin systems. Although LLSs and LLCs have been observed experimentally in methylene networks, their origin and general structure in chains of arbitrary length have remained unclear. Here we show that these relaxation-protected modes follow directly from Redfield relaxation theory. Specifically, we construct the long-lived subspace, i.e., the zero-eigenvalue subspace of the relaxation superoperator associated with the dominant intra-pair dipole--dipole relaxation mechanism. The long-lived subspace contains $2^N-1$ independent non-trivial operators, which excludes the identity operator, where $N>1$ is the number of $-\mathrm{CH}_2-$ groups in the chain. In achiral molecules, conservation of the global intra-pair permutation parity restricts experimental access to at most $2^N-2$ of these operators, whereas in chiral molecules this parity is not conserved, making up to $2^N-1$ long-lived operators accessible. We further develop a general framework for constructing both LLSs and LLCs in aliphatic chains containing an arbitrary number of $-\mathrm{CH}_2-$ groups in achiral molecules, and illustrate the approach explicitly for chains with $N=2$, 3, and 4 methylene groups.
Comments21 pages, 2 figures, 2 tables
