Optically addressable spins are actively investigated in quantum communication, processing, and sensing. Optical and spin coherence lifetimes, which determine quantum operation fidelity and storage time, are often limited by spin-spin interactions, which can be decreased by polarizing spins. Spin polarization can be achieved using optical pumping, large magnetic fields, or mK-range temperatures. Here, we show that optical pumping of a small fraction of ions with a fixed-frequency laser, coupled with spin-spin interactions and spin diffusion, leads to substantial spin polarization in a paramagnetic rare-earth doped crystal, ${{}^{171}\mathrm{Yb}}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$. Indeed, more than 90% spin polarization has been achieved at 2 K and zero magnetic field. Using this spin polarization mechanism, we further demonstrate an increase in optical coherence lifetime from 0.3 ms to 0.8 ms, due to a strong decrease in spin-spin interactions. This effect opens the way to new schemes for obtaining long optical and spin coherence lifetimes in various solid-state systems such as ensembles of rare-earth ions or color centers in diamond, which are of interest for a broad range of quantum technologies.

中文翻译：

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稀土掺杂晶体中大规模光学自旋极化的相干时间扩展

光学可寻址自旋在量子通信，处理和传感领域得到了积极研究。决定量子操作保真度和存储时间的光学和自旋相干寿命通常受到自旋-自旋相互作用的限制，而自旋-自旋相互作用可以通过使自旋极化而降低。使用光泵浦，大磁场或mK范围的温度可以实现自旋极化。在这里，我们表明，使用固定频率的激光对一小部分离子进行光泵浦，再加上自旋-自旋相互作用和自旋扩散，会导致顺磁性稀土掺杂晶体中的大量自旋极化，${{}^{171}b}^{3+}：{\mathrm{ÿ}}_2{\mathrm{二氧化硅}}_5$。实际上，在2 K和零磁场下已经实现了90％以上的自旋极化。使用这种自旋极化机制，我们进一步证明了由于自旋-自旋相互作用的强烈降低，光学相干寿命从0.3毫秒增加到0.8毫秒。这种效果为在各种固态系统（如钻石中的稀土离子或色心的集合体）中获得较长的光学和自旋相干寿命的新方案开辟了道路，这是广泛的量子技术所关注的。