The density matrix of an arbitrary pure state of a system consisting of two spin‐1/2 particles is derived from the Pauli spin angular momentum operators. Mixed singlet and triplet states are then formed from linear combinations of pure states and their corresponding density matrices constructed. Singlet and triplet states are exemplified by the spin isomers parahydrogen and orthohydrogen, respectively. Partial mixing is illustrated with the example of bilinear spin–spin coupling. Various properties of the density matrices of pure and mixed states are discussed, including idempotence, factoring, and spin correlation.

Eric R. Johnston

Concepts in Magnetic Resonance Part A

磁共振概念 A 部分汇集了参与磁共振技术应用的临床医生、化学家和物理学家。该杂志欢迎主要来自磁共振成像 (MRI)、核磁共振 (NMR) 和电子顺磁共振 (EPR) 领域的投稿，但也鼓励与不太常见的磁共振成像和分析方法相关的投稿。投稿人来自学术界，政府和临床社区，传播医学、非医学和分析磁共振方法的最新重要实验结果，以及相关的计算和理论进展。主题领域包括（但不限于）：-磁共振理解的基本进展-磁共振成像的实验结果（包括 MRI 及其专业应用）-磁共振波谱的实验结果（包括 NMR、EPR 及其专业应用）-实验的计算和理论支持与预测以结果为中心的评论提供评论和 D讨论专题研究领域的最新成果和发展-使用教程或教育方法回顾磁共振方法

Concepts in Magnetic Resonance Part A: Bridging Education and Research brings together clinicians, chemists, and physicists involved in the application of magnetic resonance technology. This journal welcomes submissions primarily from the fields of Magnetic Resonance Imaging (MRI), Nuclear Magnetic Resonance (NMR), and Electron Paramagnetic Resonance (EPR), while also encouraging contributions related to less common magnetic resonance imaging and analytical methods. Contributors come from academia, government, and the clinical community, disseminating the latest significant experimental results in medical, non-medical, and analytical magnetic resonance methods, as well as related computational and theoretical advancements. The subject areas include (but are not limited to): - Fundamental advancements in understanding magnetic resonance - Experimental results in magnetic resonance imaging (including MRI and its specialized applications) - Experimental results in magnetic resonance spectroscopy (including NMR, EPR, and their specialized applications) - Computational and theoretical support and predictions for experiments - Results-oriented reviews and discussions - Latest findings and developments in specialized research areas - Reviews of magnetic resonance methods using tutorials or educational approaches.

《Concepts in Magnetic Resonance Part A: Bridging Education and Research》汇集了参与磁共振技术应用的临床医生、化学家和物理学家。该杂志欢迎来自磁共振成像 (MRI)、核磁共振 (NMR) 和电子顺磁共振 (EPR) 领域的投稿，同时也鼓励与不太常见的磁共振成像和分析方法相关的研究。投稿人包括学术界、政府和临床社区的研究者，旨在传播医学、非医学和分析磁共振方法的最新重要实验结果，以及相关的计算和理论进展。主题领域包括（但不限于）：- 磁共振理解的基本进展 - 磁共振成像的实验结果（包括 MRI 及其专业应用） - 磁共振波谱的实验结果（包括 NMR、EPR 及其专业应用） - 实验的计算和理论支持与预测 - 以结果为中心的评论和讨论 - 专题研究领域的最新成果和发展 - 使用教程或教育方法回顾磁共振方法

Category	Quartile
化学	4
化学, 物理化学	4
化学, 物理原子、分子和化学物理	4
化学, 核医学	4
化学, 光谱学	4

Density Matrix of Two Spin‐1/2 Particles: Pure and Mixed States

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