More than a half century ago, the NMR spectra of diamagnetic products resulting from radical pair reactions were observed to have strongly enhanced absorptive and emissive resonances. At the same time, photogenerated radical pairs were discovered to exhibit unusual electron paramagnetic resonance spectra that also had such resonances. These non-Boltzmann, spin-polarized spectra were observed in both chemical systems as well as in photosynthetic reaction center proteins following photodriven charge separation. Subsequent studies of these phenomena led to a variety of chemical electron donor–acceptor model systems that provided a broad understanding of the spin dynamics responsible for these spectra. When the distance between the two radicals is restricted, these observations result from the formation of spin-correlated radical pairs (SCRPs) in which the spin–spin exchange and dipolar interactions between the two unpaired spins play an important role in the spin dynamics. Early on, it was recognized that SCRPs photogenerated by ultrafast electron transfer are entangled spin pairs created in a well-defined spin state. These SCRPs can serve as spin qubit pairs (SQPs), whose spin dynamics can be manipulated to study a wide variety of quantum phenomena intrinsic to the field of quantum information science. This Perspective highlights the role of SCRPs as SQPs, gives examples of possible quantum manipulations using SQPs, and provides some thoughts on future directions.

中文翻译：

---

光生自旋相关自由基对：从光合能量转换到量子信息科学

半个多世纪前，观察到自由基对反应产生的抗磁性产物的 NMR 光谱具有强烈增强的吸收和发射共振。同时，发现光生自由基对表现出不寻常的电子顺磁共振谱，也有这种共振。在光驱动电荷分离后，在化学系统和光合反应中心蛋白质中都观察到了这些非玻尔兹曼自旋极化光谱。随后对这些现象的研究导致了各种化学电子供体 - 受体模型系统，这些系统提供了对导致这些光谱的自旋动力学的广泛理解。当两个部首之间的距离受到限制时，这些观察结果来自自旋相关自由基对（SCRP）的形成，其中两个未配对的自旋之间的自旋-自旋交换和偶极相互作用在自旋动力学中起着重要作用。早期，人们认识到通过超快电子转移光产生的 SCRP 是在明确定义的自旋状态下产生的纠缠自旋对。这些 SCRP 可以用作自旋量子位对 (SQP)，可以操纵其自旋动力学来研究量子信息科学领域固有的各种量子现象。该视角强调了 SCRP 作为 SQP 的作用，给出了使用 SQP 进行可能的量子操作的示例，并提供了对未来方向的一些想法。人们认识到，通过超快电子转移光生的 SCRP 是在明确定义的自旋状态下产生的纠缠自旋对。这些 SCRP 可以用作自旋量子位对 (SQP)，可以操纵其自旋动力学来研究量子信息科学领域固有的各种量子现象。该视角强调了 SCRP 作为 SQP 的作用，给出了使用 SQP 进行可能的量子操作的示例，并提供了对未来方向的一些想法。人们认识到，通过超快电子转移光生的 SCRP 是在明确定义的自旋状态下产生的纠缠自旋对。这些 SCRP 可以用作自旋量子位对 (SQP)，可以操纵其自旋动力学来研究量子信息科学领域固有的各种量子现象。该视角强调了 SCRP 作为 SQP 的作用，给出了使用 SQP 进行可能的量子操作的示例，并提供了对未来方向的一些想法。