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中国物理学会期刊

多目标多约束优化超冷分子有限转动态取向

CSTR: 32037.14.aps.74.20250684

Multi-objective and multi-constraint optimization of ultracold molecular orientation with limited rotational states

CSTR: 32037.14.aps.74.20250684
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  • 设计整形脉冲场调控分子取向在立体化学反应、强场电离及量子信息处理等领域具有重要的应用价值. 然而, 传统量子最优控制算法通常在无穷维转动空间中优化分子取向度, 且未充分考虑实验设计中脉冲所需满足的约束条件. 针对这一问题, 本文提出一种多目标多约束量子最优控制算法, 用于设计满足脉冲面积和能量约束的脉冲场, 以优化超冷分子有限个低位转动态的布居和相位分布, 从而得到最大分子取向. 研究结果表明, 通过调控约束条件, 可有效抑制非目标态空间转动态的影响, 在目标态空间内获得转动态布居和相位优化的相干叠加态, 形成期望的最大分子取向. 优化脉冲的时频谱分析结合含时取向度傅里叶变换谱计算表明, 获得的最大分子取向主要通过多色脉冲场的爬梯激发实现, 且高激发态相干对最大取向度的贡献较小. 本文为利用多约束优化算法设计实验可行性脉冲场, 通过精准调控有限个转动态产生最大分子取向提供了一种可参考的方法.

     

    The design of shaping pulse fields for controlling molecular orientation is of great importance in fields of stereochemical reactions, strong-field ionization, and quantum information processing. Traditional quantum optimal control algorithms typically solve the problem of molecular orientation in an infinite-dimensional rotational space, but they often overlook the constraints imposed by experimental limitations. In this work, a multi-objective and multi-constraint quantum optimal control algorithm is proposed to design a pulse field that conforms to the constraints of pulse area and energy. Specifically, the algorithm enforces a zero pulse area condition to eliminate the static field components and maintains constant pulse energy, ensuring compatibility with realistic experimental setups. Under these constraints, the algorithm optimizes the population and phase distribution of a selected number of low-lying rotational states in ultracold molecules to achieve maximum molecular orientation. The effectiveness of the proposed algorithm is demonstrated through numerical studies involving two- and three-state target subspaces, where the creation of a coherent superposition state with optimized population and phase distribution leads to the desired molecular orientation. Furthermore, its scalability is validated by applying it to a more complex 17-state subspace, where a maximum orientation value of 0.99055 is obtained, approaching the global optimal value of 1. Our findings demonstrate that by effectively managing these constraints, the influence of rotational states in the non-target state subspace can be substantially suppressed. The time-frequency analysis of the optimized pulses, combined with the Fourier transform spectrum of the time-dependent degree of orientation, indicates that the maximum molecular orientation is mainly achieved through ladder-climbing excitation of multi-color pulse fields, with the contributions from highly excited states being minimal. This work provides a valuable reference for designing experimentally feasible pulse fields using multi-constraint optimization algorithms, which helps to precisely control a limited number of rotational states to achieve maximum molecular orientation.

     

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