Long-range exchange interaction between spin qubits mediated by a superconducting link at finite magnetic field
Long-range exchange interaction between spin qubits mediated by a superconducting link at finite magnetic field
复制标题
DOI：
10.1103/physrevb.103.035430
复制
发表时间：
2020-09
期刊：
影响因子：
--
通讯作者：
Lucia Gonzalez Rosado;F. Hassler;G. Catelani
中科院分区：
文献类型：
--
作者：
Lucia Gonzalez Rosado;F. Hassler;G. Catelani
固态自旋量子比特由于其长的相干时间和容易的电子操纵而被认为是实现量子计算机的潜在候选者。然而，纠缠门所需的自旋-自旋相互作用的范围有限，因为它们通常依赖于相邻量子点之间的隧道效应。这严重限制了可伸缩性。扩大相互作用范围的建议一般集中在点之间的相干电子传输或扩大耦合范围。在这里，我们研究一种装置，其中这样的扩展是通过使用超导体作为量子介体来获得的。由于它的间隙，超导体实际上起到了长隧道势垒的作用。我们分析了自旋-轨道(SO)耦合、外加磁场和超导体几何结构的影响。结果表明，虽然由于SO耦合引起的点与超导体之间的自旋非守恒隧穿并不影响交换作用，但在超导块体中强的SO散射是有害的。此外，我们还发现外加磁场降低了交换相互作用的强度。幸运的是，超导链路的几何形状为优化相互作用范围提供了很大的空间，从2D薄膜到准1D条带的增益超过一个数量级。我们估计，对于具有弱SO耦合(例如，铝)的超导体，在100 mT量级的磁场存在的情况下，利用这种装置可以在微米级范围内获得高达100 MHz的交换率。
Solid state spin qubits are promising candidates for the realization of a quantum computer due to their long coherence times and easy electrical manipulation. However, spin-spin interactions, which are needed for entangling gates, have only limited range as they generally rely on tunneling between neighboring quantum dots. This severely constrains scalability. Proposals to extend the interaction range generally focus on coherent electron transport between dots or on extending the coupling range. Here, we study a setup where such an extension is obtained by using a superconductor as a quantum mediator. Because of its gap, the superconductor effectively acts as a long tunnel barrier. We analyze the impact of spin-orbit (SO) coupling, external magnetic fields, and the geometry of the superconductor. We show that while spin non-conserving tunneling between the dots and the superconductor due to SO coupling does not affect the exchange interaction, strong SO scattering in the superconducting bulk is detrimental. Moreover, we find that the addition of an external magnetic field decreases the strength of the exchange interaction. Fortunately, the geometry of the superconducting link offers a lot of room to optimize the interaction range, with gains of over an order of magnitude from a 2D film to a quasi-1D strip. We estimate that for superconductors with weak SO coupling (\textit{e.g.}, aluminum) exchange rates of up to 100\,MHz over a micron-scale range can be achieved with this setup in the presence of magnetic fields of the order of 100\,mT.