原子光钟跃迁性质的相对论耦合簇理论计算

Optical frequency standards based on single a trapped ion or neutral atoms in optical lattice can reach a systematic fractional uncertainty above the order of 10-18. Some of the successful single-ion optical atomic clocks include Ca+, Hg+, Al+, etc, and the successful optical-lattice clocks include Sr and Yb. A new range of experiments are also proposed for other ions or neutral atoms like Ba+, Ra+, In+, Yb+, Mg, and Ca, etc. More precise time and frequency standards will open up possibilities to study the underlying physics related to fundamental constants, probing new elementary physics, and, more importantly, it can help in improving the present-day positing systems and also in tracking deep-space probes...At such high frequency level, the major contributions to systematic frequency uncertainty come from high-order perturbations of atomic state in the external magnetic, optical, and electric fields. Therefore, interests in the subject of high-precise calculation of atomic states has been recently elevated by the appreciation that the accuracy of next-generation atomic time and frequency standards, based on optical transition, is significantly limited by the displacement of atomic energy levels due to universal ambient fluctuations in the external fields. Determination of optical transition frequency depends on intrinsic properties of atoms and ions such as the electric dipole matrix elements, polarization, quadruple moment, and excitation energies, etc. Accurate evaluation of these quantities, in particular for heavy atoms, requires all-order approaches where dominant electron correlation terms are summed to all orders of many-body perturbation theory...We aim to study properties of optical atomic transition of Ca+, Al+, Hg+, Sr and Yb by considering QED effects in the frame of general-order relativistic coupled cluster method. The shifts in the atomic energy levels due to the Zeeman effect, the Stark effect, the quadrupole polarization, and the black-body radiation are calculated. In the optical lattice system, the optical Stark frequency shift is calculated, which further helps us to find the magic-wavelength laser. Our calculations will also provide reliable theoretical data of atom and ion structure such as the static scalar and tensor polarization, the dyanmic polarization, the quadruple polarization, the hyperfine structure constant, the electron and nuclear g factor, etc. Our research results will helps experimentists to evaluate energy shifts in transition frequency and then give a budget of uncertainties and stability for their optical atomic clock.

束缚单离子光钟和光晶格原子光钟将时间频率的定义提高到极限水平。在这个层次上，原子光频标的不准确度和稳定性受到更细微的影响因素的限制。为了确定新一代的时间频率标准，影响原子光频标的钟频率跃迁性质的高阶小量必须经过评估、计算和修正。 目前原子光钟的候选原子包括Ca+,Al+,Hg+,Sr,Yb等，大都具有复杂的电子多重态和准简并性，旋轨耦合效应使高精度价电子能谱和跃迁性质的计算问题更加复杂。在这样的背景下，我们选择束缚单离子和光晶格中性原子为研究对象，发展基于束缚态量子电动力学理论的多电子体系精密能谱计算方法，考虑相对论效应和多电子相干效应，研究Ca+,Al+,Hg+,Sr,Yb等的跃迁性质，计算磁、光、电外场扰动下原子和离子跃迁能级的各种高阶小量，如二阶塞曼频移、斯塔克频移、电四极频移，光频移和寻找魔波长，为我国原子光频标的实验误差物理起源的分析以及不准确度和稳定性评估提供理论数据。

近五年来，基于Al+ 离子、Sr原子、Yb原子光钟的时间频率精密测量的不确定度已经提高到了10-18的水平，基于高价离子的新一代光钟将达到10-19甚至更高的极限水平。一方面，时间频率精度达到10-18的量级时将可以直接验证自然界的基本物理定律，具有重要科学意义。另一方面，当时间频率测量的精度到达如此高的水平时，更细微和新的效应会显现出来。频率的不确定度是衡量光频标精度的一个重要指标，其物理起源在于环境对原子能级的干扰以及与原子运动有关的各种效应，即“频移”。. 本项目研究内容围绕时频测量不确定度达到10–18极限水平和这一具体科学目标，发展相对论耦合簇计算方法，研究原子光频标候选原子钟跃迁的基态和激发态性质，计算原子结构重要参数，计算影响原子光频标准确度和稳定性的高阶微扰小量，理论与实验结合，建立原子光频标的误差评估和理论模型。重要结果包括Al+光钟的极化性质和黑体辐射频移；In+和Sr的自旋角动量分辨的偶极极化率、超极化率、电四极矩和电四极矩极化率的推荐值，静态偶极极化率、超极化率和电四极极化率导致的背景黑体辐射频移的量级的精确评估；一个典型的过渡族重元素Ir的氧化物电子结构和光谱多参考态全相对论组态相干计算，为下一步基于超冷分子的精密测量物理和能谱计算提供不可或缺的基本经验；用于10-19精度量级的原子钟的类铝51V10+，53Cr11+，55Mn12+，57Fe13+，59Co14+，61Ni15+和63Cu16+高价离子的不确定性评估;新一代高价离子光钟的能级交叉和新的候选体系研究。. 本项目给出了Al+, In+, Sr和7类高价离子的极化率、黑体辐射频移、二阶Zeeman频移等高精度数据，为相关原子光频标的实验误差分析和准确度以及稳定性评估提供了理论依据。

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