超导量子计算芯片制备及功能测试

无论对于哪种类型的量子比特，要想实现通用量子计算就得准确识别并抑制影响量子比特退相干的因素。基于约瑟夫森结，我们可以灵活的设计量子比特的参数。但是这种超导量子比特将不可避免的遭受一种叫准粒子的噪声的影响。在超导量子比特中，我们把被破坏的库珀对称为准粒子。实验已经证明，实际器件中的准粒子密度远大于理论预测。因此，在如今多量子比特集成的趋势下，需要对非平衡态准粒子的产生机制有更深刻的理解，以进一步抑制准粒子的影响。该论文中，我们实验上研究了如何通过控制量子比特的几何结构来控制芯片上准粒子的产生。实验中我们可以把由于准粒子隧穿引起的电荷宇称转变速率压制到 1 Hz 以下。同时，我们的样品还进一步提升了电荷稳定性。我们的实验结果可以由超导量子比特天线模型理论进行解释，并据此模型，我们设计出了一种易设计、可扩展的 3D 超导量子比特样品。在这种样品上，准粒子的产生会被极大的抑制，对提升量子比特退相干，实现容错量子计算具有重要意义。

In any physical realization of a qubit, identifying, quantifying, and suppressing mechanisms of decoherence are important steps towards the goal of engineering a universal quantum computer or a quantum simulator. Superconducting circuits based on Josephson junctions offer flexibility in qubit design; however, their performance is adversely affected by quasiparticles (broken Cooper pairs) whose density, as observed in various systems, is considerably higher than that expected in thermal equilibrium. A full understanding of the generation mechanism and a mitigation strategy that is compatible with scalable, high-coherence devices are therefore highly desirable. Here we experimentally demonstrate how to control quasiparticle generation by downsizing the qubit structure, capping it with a metallic cover, and equipping it with suitable quasiparticle traps. We achieve record low charge-parity switching rate (< 1 Hz) in our aluminium devices. At the same time, the devices display improved stability with respect to discrete charging events. Our findings support the hypothesis that the generation of quasiparticles is dominated by the breaking of Cooper pairs at the junction, as a result of photon absorption mediated by the antenna-like qubit structure. We thus demonstrate a convenient approach to shape the electromagnetic environment of superconducting circuits in the sub-terahertz regime, inhibiting decoherence from quasiparticle poisoning.

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