Tunnel Junction Characterization and Optimization for Quantum Computing Applications

量子计算有望给现代信息时代带来革命性变化。最先进的量子计算平台之一使用超导量子比特。与利用囚禁离子和光子等基本粒子的其他量子计算技术相比，超导量子比特是在宏观电磁电路中利用长程多体波函数实现的。这使得超导量子比特可以被设计成实现许多所需的性质，例如量子比特、控制电子学和环境浴之间的可调耦合。就像传统逻辑电路的晶体管一样，超导量子比特的核心部件是约瑟夫森结。这些器件是利用两个超导电极之间的薄氧化层实现的。电路中的噪声和损耗对此势垒中的缺陷指数敏感。例如，氧化物势垒内或附近的单原子缺陷可能会在位置上波动，导致隧穿速率中的低频噪声(1/f噪声)。另一个故障是绝缘体屏障中存在非常小的断裂，通常被称为“针孔”，这可能会导致从一根超导导线到另一根导线的微小电流泄漏。在这个项目中，我们计划与加拿大领先的量子计算技术公司D-Wave Systems合作，开发几种关键的表征工具，用于在50 MK的工作温度(比绝对零度低0.1度)下评估亚微米约瑟夫森结。然后，这些工具将用于优化约瑟夫森结的制造工艺，重点是将1/f噪声、射频损耗和泄漏电流降至最低。结质量的改善将通过测量D波超导量子比特来评估，我们最终预计会看到性能的显着提高。

Quantum computing promises to revolutionize the modern information age. One of the most advanced quantum computing platforms uses superconducting qubits. Compared with other quantum computing technologies utilizing fundamental particles such as trapped ions and photons, superconducting qubits are implemented with the long range many-body wavefunction in a macroscopic electromagnetic circuit. This allows superconducting qubits to be engineered to realize a multitude of desirable properties such as tunable coupling between qubits, control electronics, and the environmental bath. Much like the transistor for conventional logical circuits, the core component of superconducting qubits is the Josephson junction. These devices are realized using a thin oxide barrier between two superconducting electrodes. The noise and dissipation in the circuit is exponentially sensitive to defects in this barrier. For example, single atomic defects within or in the vicinity of the oxide barrier can fluctuate in position causing a low frequency noise (1/f noise) in the tunneling rate. Another fault is the existence of very small breaks in the insulator barrier, commonly known as "pin holes", that can cause a small current leakage from one superconducting lead to the other. In this project, working with D-Wave Systems, a leading quantum computing technology company based in Canada, we plan to develop several key characterization tools for assessing sub-micron Josephson junctions at a 50 mK operating temperature (below a tenth of a degree above absolute zero). These tools will then be used to optimize the Josephson junction fabrication process, focusing on minimizing 1/f noise, rf losses, and leakage currents. The improvements in junction quality will then be assessed by measuring D-Wave superconducting qubits where we ultimately expect to see significant gains in performance.