论文标题
与不对称连接的超导Qubits中的准粒子
Quasiparticles in superconducting qubits with asymmetric junctions
论文作者
论文摘要
长期以来，设计超导间隙的空间轮廓 - 差距工程 - 已被认为是在超导器件中控制准粒子的有效方法。在铝制膜中，它们的厚度调节了间隙。因此，依赖于较薄的薄膜重叠的Al/Alox/Al Josephson连接的标准制造始终会导致间隙工程设备。在这里，我们重新考虑了超导Qubits中的准粒子效应，以明确说明约瑟夫森交界处两侧的间隙中不可避免的不对称性。我们发现，可以遇到不同的机制，即准颗粒在两个连接线中具有相似的密度，或者在很大程度上局限于较低间隙的引线。在定性上，对于类似的密度，Qubit的激发状态人口较低，但其放松率高于限制准粒子时。因此，在量子空的两个理想特性之间存在潜在的权衡。
Designing the spatial profile of the superconducting gap -- gap engineering -- has long been recognized as an effective way of controlling quasiparticles in superconducting devices. In aluminum films, their thickness modulates the gap; therefore, standard fabrication of Al/AlOx/Al Josephson junctions, which relies on overlapping a thicker film on top of a thinner one, always results in gap-engineered devices. Here we reconsider quasiparticle effects in superconducting qubits to explicitly account for the unavoidable asymmetry in the gap on the two sides of a Josephson junction. We find that different regimes can be encountered in which the quasiparticles have either similar densities in the two junction leads, or are largely confined to the lower-gap lead. Qualitatively, for similar densities the qubit's excited state population is lower but its relaxation rate higher than when the quasiparticles are confined; therefore, there is a potential trade-off between two desirable properties in a qubit.
