Optimal control theory is a powerful tool for solving control problems in quantum mechanics, ranging from the control of chemical reactions to the implementation of gates in a quantum computer. Gradient-based optimization methods are able to find high fidelity controls, but require considerable numerical effort and often yield highly complex solutions. We propose here to employ a two-stage optimization scheme to significantly speed up convergence and achieve simpler controls. The control is initially parametrized using only a few free parameters, such that optimization in this pruned search space can be performed with a simplex method. The result, considered now simply as an arbitrary function on a time grid, is the starting point for further optimization with a gradient-based method that can quickly converge to high fidelities. We illustrate the success of this hybrid technique by optimizing a holonomic phasegate for two superconducting transmon qubits coupled with a shared transmission line resonator, showing that a combination of Nelder-Mead simplex and Krotov's method yields considerably better results than either one of the two methods alone.
Benchmarking simulation of hybrid decoding scheme for parity-encoded spin systems
NEC-AIST Quantum Technology Cooperative Research Laboratory（NEC-AIST量子技术联合研究实验室）；National Institute of Advanced Industrial Science and Technology（国立产业技术综合研究所）
Role of exact exchange in thermally-assisted-occupation density functional theory: A proposal of new hybrid schemes
我们提出了将精确交换结合到热辅助占据密度泛函理论（TAO-DFT）中的混合方案[J. - D. Chai，J.Chem.Phys.136，154104（2012）]，以改进对非局部交换效应的描述。通过一些简单的修改，Kohn-Sham密度泛函理论（KS-DFT）中的整体和距离分离的杂化泛函可以与TAO-DFT无缝结合。与KS-DFT中的全局混合泛函相比，TAO-DFT中所得的全局混合泛函对于具有强静态相关效应的系统（例如，H2和N2的解离、扭曲乙烯和线性并苯的电子性质），同时对于没有强静态相关效应的系统保持类似的性能。此外，通过在混合TAO-DFT中引入色散校正，可以有效地实现对非共价相互作用的合理准确描述。相对于TAO-DFT中的半局域密度泛函，TAO-DFT中的全局杂化泛函在热化学、动力学、反应能和优化几何结构等广泛的应用中表现出优越的性能.
Monte Carlo Tree Search based Hybrid Optimization of Variational Quantum Circuits
University of California, Berkeley（加州大学伯克利分校）；Stanford University（斯坦福大学）；St. Kliment Ohridski University of Sofia（索非亚圣克里门特·奥赫里德大学）；Max Planck Institute for the Physics of Complex Systems（马克斯·普朗克复杂系统物理研究所）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
