Seo Hosung, Falk Abram L, Klimov Paul V, Miao Kevin C, Galli Giulia, Awschalom David D
The Institute for Molecular Engineering, The University of Chicago, Chicago, Illinois 60615, USA.
IBM T.J. Watson Research Center, Yorktown Heights, New York 10598, USA.
Nat Commun. 2016 Sep 29;7:12935. doi: 10.1038/ncomms12935.
Long coherence times are key to the performance of quantum bits (qubits). Here, we experimentally and theoretically show that the Hahn-echo coherence time of electron spins associated with divacancy defects in 4H-SiC reaches 1.3 ms, one of the longest Hahn-echo coherence times of an electron spin in a naturally isotopic crystal. Using a first-principles microscopic quantum-bath model, we find that two factors determine the unusually robust coherence. First, in the presence of moderate magnetic fields (30 mT and above), the Si and C paramagnetic nuclear spin baths are decoupled. In addition, because SiC is a binary crystal, homo-nuclear spin pairs are both diluted and forbidden from forming strongly coupled, nearest-neighbour spin pairs. Longer neighbour distances result in fewer nuclear spin flip-flops, a less fluctuating intra-crystalline magnetic environment, and thus a longer coherence time. Our results point to polyatomic crystals as promising hosts for coherent qubits in the solid state.
长相干时间是量子比特（qubit）性能的关键。在此，我们通过实验和理论证明，与4H-SiC中的双空位缺陷相关的电子自旋的哈恩回波相干时间达到1.3毫秒，这是天然同位素晶体中电子自旋最长的哈恩回波相干时间之一。使用第一性原理微观量子浴模型，我们发现有两个因素决定了这种异常稳健的相干性。首先，在中等磁场（30 mT及以上）存在的情况下，Si和C顺磁核自旋浴解耦。此外，由于SiC是二元晶体，同核自旋对既被稀释又被禁止形成强耦合的最近邻自旋对。更长的相邻距离导致更少的核自旋翻转，晶体内磁环境波动更小，从而相干时间更长。我们的结果表明，多原子晶体有望成为固态中相干量子比特的宿主。
