Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits
Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits
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DOI：
10.1063/5.0037093
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发表时间：
2021-02-08
影响因子：
4
通讯作者：
Roudsari, A. Fadavi
中科院分区：
文献类型：
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作者：
Osman, A.;Simon, J.;Roudsari, A. Fadavi
我们介绍了一种简化的约瑟夫森结的制造技术，并展示了超导Xmon量子比特的T-1弛豫时间平均超过50 μ s（Q > 1.5 × 106）。目前用于铝基约瑟夫逊结的阴影蒸发技术需要单独的光刻步骤来存款在结电极和电路布线层之间形成电流超导连接的贴片。贴片连接消除了寄生结，否则寄生结会显著增加介电损耗。在我们的贴片集成交叉型结技术中，我们使用一个光刻步骤和一个真空循环来蒸发结电极和贴片。这通过减少制造时间和成本消除了制造超导量子比特的关键瓶颈。在对3600多个结的研究中，我们发现在含有40个0.5 × 0.5-cm（2）芯片的晶片上，结面积在0.01和0.16 μ m（2）之间，平均电阻变化为3.7%。电阻的平均片上分布为2.7%，20个芯片在1.4%和2%之间变化。对于用于transmon量子比特的结尺寸，我们推导出1.7%-2.5%的晶片级跃迁频率变化。我们发现，这种变化的60%-70%是由于结面积波动，而其余的是由隧道结的不均匀性。这种高频率的可预测性是在量子计算机中按比例增加量子比特数量的要求。
We introduce a simplified fabrication technique for Josephson junctions and demonstrate superconducting Xmon qubits with T-1 relaxation times averaging above50mu s (Q > 1.5 x 106). Current shadow-evaporation techniques for aluminum-based Josephson junctions require a separate lithography step to deposit a patch that makes a galvanic, superconducting connection between the junction electrodes and the circuit wiring layer. The patch connection eliminates parasitic junctions, which otherwise contribute significantly to dielectric loss. In our patch-integrated cross-type junction technique, we use one lithography step and one vacuum cycle to evaporate both the junction electrodes and the patch. This eliminates a key bottleneck in manufacturing superconducting qubits by reducing the fabrication time and cost. In a study of more than 3600 junctions, we show an average resistance variation of 3.7% on a wafer that contains forty0.5 x 0.5-cm(2) chips, with junction areas ranging between 0.01 and 0.16 mu m(2). The average on-chip spread in resistance is 2.7%, with 20 chips varying between 1.4% and 2%. For the junction sizes used for transmon qubits, we deduce a wafer-level transition-frequency variation of 1.7%-2.5%. We show that 60%-70% of this variation is attributed to junction-area fluctuations, while the rest is caused by tunnel-junction inhomogeneity. Such high frequency predictability is a requirement for scaling-up the number of qubits in a quantum computer.