基于线路量子电动力学的容错量子计算研究

The realization of quantum computer will cause new revolution of information technology. As it is well-known, high-fidelity quantum logical operation is the basic element of universal quantum computation and the essential element for its physical realization. Geometric phases are determined by the global feathers of the evolution system, avoiding the influence of certain local noises, thus can be used to realize high-fidelity quantum control, which can be adopted in quantum computation. But, previous study on nonabelian geometric quantum computation mainly based on multilevel quantum system, where the construction of two-qubit quantum gates is very complicated. In recent years, the applicant has proposed series schemes for nonadiabatic holonomic quantum computation based on superconducting circuits with (effective) three level systems. However, since the superconducting transmon qubit is only weakly anharmonic and the coherent times are relatively short, high-fidelity and fault-tolerant quantum computation still needs further exploration. In this project, through frequency selection to tune the inter-qubit interactions, we intend to study the physical realization of large scale nonadiabatic geometric quantum computation, using microwave fields to drive qubits. Meanwhile, through modulation of the pulse shape of the driving microwave fields, we can further suppress the leakage of the quantum information, the errors due to the control imperfection and systematic errors, and thus further enhance the operational fidelity. Therefore, our study will provide theoretical support and experimental guidance for fault-tolerant quantum computation on superconducting circuits.

量子计算机的实现将引起信息技术的新变革。高保真度的量子逻辑门是普适量子计算的基本单元也是其物理实现的关键。几何相位由演化系统的整体性质决定，避免了某些局域噪声的影响，可以用来实现高保真度的量子操控。然而，前期基于非阿贝尔几何相位的量子计算方案大多在多能级体系中实现，其两比特逻辑门的构造十分复杂。近年来，申请者提出了基于超导体系（等效）三能级体系非绝热和乐量子计算的系列实现方案。然而，由于超导体系非线性较小、相干时间较短，高保真度的容错量子计算有待于深入研究。本项目拟通过对超导比特的微波驱动，通过频率选择来调节比特间的相互作用强度，研究大规模非绝热几何量子计算的物理实现。同时，通过对驱动微波脉冲的调制，可以达到抑制比特信息泄露、控制误差以及系统误差等目的，进一步提高几何量子门的保真度。因此，本项目的研究为超导系统中实现容错量子计算提供必要的理论支持与实验依据。

量子信息技术是可能突破摩尔定律极限的关键技术之一，具有重要的学术价值和潜在应用前景。项目的研究以“量子计算机研制”这一国家重大战略需求为导向，研究聚焦于固态几何量子计算，特别注重理论探索和实验研究相结合。项目按照研究计划执行，完成了全部研究内容，包括超导量子芯片上基于参数可调耦合的几何与和乐量子计算与量子模拟的理论与实验研究；基于复合脉冲、优化控制、时间最优化、路径优化等技术的几何与和乐量子计算的理论与实验研究；基于编码子空间的几何与和乐量子计算及其物理实现。同时，我们也额外开展了基于超导体系的拓扑量子模拟以及基于半导体量子点量子比特的几何与和乐量子计算。. 项目的研究证明几何量子门在鲁棒性和保真度两个关键指标方面具有优势，为未来大规模量子计算的构建提供了更好的备选方案。项目的理论成果得到了国内外知名实验组在Physical Review Letters等期刊上发表的10个实验的直接验证或应用，有力地促进了几何量子计算理论与实验的发展。项目的研究成果发表科研论文42篇，包括Physical Review Letters 3 篇，npj Quantum Information和Quantum Science and Technology 各1篇，Physical Review Applied 11篇，Physical Review A 9篇。项目的研究成果获得了国内外同行的广泛关注和认可，被Reviews of Modern Physics，Nature Physics，Physical Review Letters 等SCI核心集期刊广泛引用。. 项目执行期间培养培养博士后2人，博士3人，硕士6人，硕士生转硕博连读4人，使他们得到了全程的科研训练，博士后和博士毕业生目前均在高校工作。