Title: Superexchange coupling of donor qubits in silicon Show Chinese title

Title: 掺杂剂量子比特在硅中的超交换耦合

Abstract: Atomic engineering in a solid-state material has the potential to functionalize the host with novel phenomena. STM-based lithographic techniques have enabled the placement of individual phosphorus atoms at selective lattice sites of silicon with atomic precision. Here, we show that by placing four phosphorus donors spaced 10-15 nm apart from their neighbours in a linear chain, it is possible to realize coherent spin coupling between the end dopants of the chain, analogous to the superexchange interaction in magnetic materials. Since phosphorus atoms are a promising building block of a silicon quantum computer, this enables spin coupling between their bound electrons beyond nearest neighbours, allowing the qubits to be spaced out by 30-45 nm. The added flexibility in architecture brought about by this long-range coupling not only reduces gate densities but can also reduce correlated noise between qubits from local noise sources that are detrimental to error correction codes. We base our calculations on a full configuration interaction technique in the atomistic tight-binding basis, solving the 4-electron problem exactly, over a domain of a million silicon atoms. Our calculations show that superexchange can be tuned electrically through gate voltages where it is less sensitive to charge noise and donor placement errors. Show Chinese abstract

Abstract: 在固态材料中进行原子工程有可能使宿主材料具备新颖的特性。基于扫描隧道显微镜的光刻技术已经实现了在硅的晶格位点上以原子精度放置单个磷原子。在这里，我们展示通过将四个磷供体原子以10-15纳米的间距排列成线性链，可以在链的末端供体之间实现相干自旋耦合，这类似于磁性材料中的超交换相互作用。由于磷原子是硅量子计算机的有前途的构建模块，这使得它们的束缚电子之间的自旋耦合可以超越最近邻，允许量子比特之间的间距达到30-45纳米。这种远距离耦合带来的架构灵活性不仅减少了门密度，还可以减少来自对纠错码有害的局部噪声源的量子比特之间的相关噪声。我们的计算基于原子紧束缚基组中的全组态相互作用技术，精确求解了一个包含一百万个硅原子区域内的四电子问题。我们的计算表明，可以通过栅极电压调节超交换作用，使其对电荷噪声和供体位置误差不那么敏感。