适合容错量子计算的高性能超导量子比特的研制与调控

Superconducting qubits are Josephson-junction based circuits that can simulate the quantum behavior of atoms. They can be well controlled using sophisticated microwave signals, and can be flexibly tailored and scaled up using the silicon-based microfabrication. Over the past decade huge efforts in materials research and circuit engineering have greatly improved the overall performance of superconducting qubits, which truly places the system close to the fault-tolerant threshold for quantum computing. In particular, a recent experiment (Nature 508, 500-503 (2014)) has achieved an average single-qubit gate fidelity of 99.92% and a two-qubit gate fidelity up to 99.4%. In our proposal, we will take the challenge to develop the high-performance superconducting qubits suitable for fault-tolerant quantum computing. Based upon our previous research experience, we emphasize the importance of optimization in the design and fabrication of superconducting qubits. We will fabricate high-quality Josephson junctions with small junction areas in ultra-high vacuum deposition systems, and meanwhile will strive to minimize the complexity of the peripheral circuitry with just enough controllability for the qubit. In our developed multi-qubit circuit, we will try to demonstrate high-fidelity gate operations and perform the feedback controls based on quantum non-demolition measurement. Novel quantum phenomena associated with the new multi-qubit architecture will also be explored.

超导量子比特是可以模拟原子行为的约瑟夫森结电路。它基于硅材料工艺，使用微波精确调控，方便集成。近年来在材料学和电子工程学方面的研究大大提升了超导量子比特的综合性能，使其成为实现容错量子计算的有力候选。最近国际上普适单比特和双比特运算门的精度分别达到了99.92%和99.4%（Nature 508, 500-503 (2014)），逼近容错量子计算阈值。在本申请项目中，我们将基于自己的样品制备经验研发适合容错量子计算的高性能超导量子比特。我们将优化样品设计和各种制备工艺参数，制备高质量的约瑟夫森结，重点是缩小结的面积和利用超高真空镀膜设备。我们同时将简化约瑟夫森结周围的辅助电路，在保证量子门操控的前提下最大程度地削弱外围电路对结的控制。最后在基于新理念制备的多比特量子器件中，我们将争取展示高精度的多比特运算门操作和多体纠缠、以及基于非破坏性测量的实时量子反馈。同时我们也将探究基于新器件的多体物理问题。

超导量子比特是可模拟原子行为的超导约瑟夫森结电路。它基于微加工工艺、使用微波精确调控、方便集成。近年来在材料学和电子工程学方面的研究大大提升了超导量子比特的综合性能，使其成为实现量子计算的有力候选体系。在本项目中，我们重点研发了高性能的超导量子比特，并奠定了针对其实现高精度操纵的技术基础。通过优化器件构型和制备工艺参数，我们设计制备了高质量的集成多比特的超导量子芯片：芯片采用全连通架构，比特集成数多至20个，比特退相干时间在20-50微秒区间。同时我们发展了多通道、高精度的弱微波脉冲信号发射和捕捉技术，研发了能用于20比特同步高精度读取的量子放大器，实验制备并标定了18比特的Greenberger-Horne-Zeilinger（GHZ）纠缠态和20比特的多组份薛定谔猫态【Science 365, 574 (2019)】，其中18比特GHZ态保真度超过50%的量子纠缠阈值，创造了固态体系纠缠粒子数的记录。利用自主设计制备的多比特量子芯片，我们进一步展示了高精度的多比特运算门操作，探究了诸如多体局域化、手征特性和任意子编结等基础物理问题，初步展示了超导量子比特用于量子模拟研究的前景。项目执行期间已发表受项目资助的论文19篇（含接收1篇），其中Science 1篇，Nature Physics 1篇，Nature Communications 1篇，Science Advances 1篇，Physical Review Letters 9篇（含接收1篇）。项目培养杰青1名，以及多名有潜质的热衷于推动该领域发展的博士硕士毕业生和在读学生，顺利完成了针对面向量子计算的若干前瞻性理论和技术的探索和验证。