主动自旋晶格超极化：应用于六方氮化硼色心
Active spin lattice hyperpolarization: Application to hexagonal boron nitride color centers
AI总结：
本文研究通过主动驱动中心自旋使核自旋浴超极化的效率，利用Holstein-Primakoff近似扩展到大自旋系统，并证明该方法可在六方氮化硼$V_B$色心中实现硼和氮核自旋晶格的高度超极化，为二维量子模拟器和延长相干时间奠定基础。
摘要：
主动驱动色心电子自旋被认为是使周围核自旋浴超极化并初始化包含大量自旋的系统的一种方法。在此，我们研究了该方法在耦合到中心自旋的一维海森堡链中针对各种自旋耦合方案的效率。为了将研究扩展到具有大量相互作用自旋的现实系统，我们采用了一种基于Holstein-Primakoff变换的近似方法。该方法描述自旋极化动力学的有效性通过小晶格上的精确数值计算进行了基准测试，其中玻色子Holstein-Primakoff近似方法的准确性得到了确认。因此，我们将分析扩展到精确数值计算无法触及的更大自旋系统。结果表明，当中心自旋与自旋浴的相互作用是长程的，并且自旋浴中自旋间相互作用足够大时，主动驱动方法是高效的。随后，该方法被应用于六方氮化硼中光学活跃的带负电硼空位中心（$V_B$）这一现实情形。我们的结果表明，即使从完全热化的自旋浴开始，也可以在硼和氮核自旋晶格中实现高度的超极化。作为初始化步骤，我们的工作为实现基于天然核自旋的二维量子模拟器迈出了第一步，并且可能有助于延长$V_B$中心的相干时间。
英文摘要：
The active driving of the electron spin of a color center is known as a method for the hyperpolarization of the surrounding nuclear spin bath and to initialize a system with large number of spins. Here, we investigate the efficiency of this approach for various spin coupling schemes in a one-dimensional Heisenberg chain coupled to a central spin. To extend our study to the realistic systems with a large number of interacting spins, we employ an approximate method based on Holstein-Primakoff transformation. The validity of the method for describing spin polarization dynamics is benchmarked by the exact numerics for a small lattice, where the accuracy of the bosonic Holstein-Primakoff approximation approach is confirmed. We, thus, extend our analysis to larger spin systems where the exact numerics are out of reach. The results prove the efficiency of the active driving method when the central spin interaction with the spin bath is long range and the inter-spin interactions in the bath spins is large enough. The method is then applied to the realistic case of optically active negatively charged boron vacancy centers ($V_B$) in hexagonal boron nitride. Our results suggest that a high degree of hyperpolarization in the boron and nitrogen nuclear spin lattices is achievable even starting from a fully thermal bath. As an initialization, our work provides the first step toward the realization of a two-dimensional quantum simulator based on natural nuclear spins and it can prove useful for extending the coherence time of the $V_B$ centers.
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