Improvement of Stability of ~(40)Ca~+ Optical Clock with State Preparation

Stability is one of most important performances of an atomic clock. Here we describe our recent work on improving the stability of our 40 Ca+ optical clock. State preparation is adopted to transfer the ion to the groundstate magnetic sublevel of the clock transition, after the quenching laser transfers the ion to the ground state at each cycle. Using this method,the stability for ~(40)Ca~+ optical clock is improved to about 6.3 × 10~(-15)/τ~(1/2).Compared with 1.0 × 10~(-14)/τ~(1/2) in previous work, the averaging time is decreased to reach a given level of statistical uncertainty in a clock comparison.     

Precision spectroscopy with a single ~(40)Ca~+ ion in a Paul trap

Precision measurement of the 4s2S1/2–3d2D5/2clock transition based on40Ca+ion at 729 nm is reported. A single40Ca+ion is trapped and laser-cooled in a ring Paul trap, and the storage time for the ion is more than one month. The linewidth of a 729 nm laser is reduced to about 1 Hz by locking to a super cavity for longer than one month uninterruptedly.The overall systematic uncertainty of the clock transition is evaluated to be better than 6.5×10-16. The absolute frequency of the clock transition is measured at the 10-15 level by using an optical frequency comb referenced to a hydrogen maser which is calibrated to the SI second through the global positioning system(GPS). The frequency value is 411 042 129776 393.0(1.6) Hz with the correction of the systematic shifts. In order to carry out the comparison of two40Ca+optical frequency standards, another similar40Ca+optical frequency standard is constructed. Two optical frequency standards exhibit stabilities of 1×10-14τ-1/2with 3 days of averaging. Moreover, two additional precision measurements based on the single trapped40Ca+ion are carried out. One is the 3d2D5/2state lifetime measurement, and our result of 1174(10) ms agrees well with the results reported in [Phys. Rev. A 62 032503(2000)] and [Phys. Rev. A 71 032504(2005)]. The other one is magic wavelengths for the 4s2S1/2–3d2D5/2clock transition; λ|m j|=1/2= 395.7992(7) nm and λ|m j|=3/2=395.7990(7) nm are reported, and it is the first time that two magic wavelengths for the40Ca+clock-transition have been reported.     

Relationship measurement between ac-Stark shift of ~(40)Ca~+ clock transition and laser polarization direction

Ac-Stark shift of atom levels is caused by an ac-electromagnetic field. As an electromagnetic wave, laser light does induce ac-Stark shift. It is proved experimentally that if the light is linearly polarized, the dynamic polarizability changes with polarization direction. The polarization direction of the linearly-polarized laser is tuned by 720?, and the ac-Stark shifts of the 4S_(1/2),m=±1/2→3D_(5/2,m=±1/2) clock transitions in ~(40)Ca~+ are measured in steps of 10?. The frequency shifts change with laser polarization in a periodical manner and have values opposite to each other.     

Sympathetic Cooling of ~(40)Ca~(+_27)Al~+ Ion Pair Crystal in a Linear Paul Trap

The ~(27)Al~+ ion optical clock is one of the most attractive optical clocks due to its own advantages such as low black-body radiation shift at room temperature and insensitivity to the magnetic drift.However,it cannot be laser-cooled directly in the absence of 167 nm laser to date.This problem can be solved by sympathetic cooling.In this work,a linear Paul trap is used to trap both ~(40)Ca~+ and ~(27)Al~+ ions simultaneously,and a single Dopplercooled ~(40)Ca~+ ion is employed to sympathetically cool a single ~(27)Al~+ ion.Thus a 'bright-dark' two-ion crystal has been successfully synthesized.The temperature of the crystal has been estimated to be about 7mK by measuring the ratio of carrier and sideband spectral intensities.Finally,the dark ion is proved to be an ~(27)Al~+ ion by precise measuring of the ion crystal's secular motion frequency,which means that it is a great step for our ~(27)Al~+ quantum logic clock.     

Predictions for cross sections of light proton-rich isotopes in the ~(40)Ca + ~9Be reaction

The cross sections for Z=10–19 with isotopes T_z=-3/2 to-5 in the 140A Me V~(40)Ca+~9Be projectile fragmentation reaction have been predicted.An empirical formula based on the correlation between the cross section and average binding energy of an isotope has been adopted to predict the cross section.The binding energies in the AME16,WS4,and the theoretical prediction by the spherical relativistic continuum Hartree-Bogoliubov theory have been used.Meanwhile,the fracs parametrization and the modified statistical abrasion-ablation model are also used to predict the cross sections for the proton-rich isotopes.The predicted cross sections for the T_z=-3 isotopes are close to 10~(-10)mb,which hopefully can be studied experimentally.In addition,based on the predicted cross sections,Z=14 is suggested to be a new magic number in the light proton-rich nuclei with T_z-3/2,for which the phenomenon is much more evident than it is from the average binding energy per nucleon.     

Entrance-channel dynamics in the reaction ~(40)Ca+~(208)Pb

The entrance-channel dynamics including capture, fusion, and quasifission processes for the reaction ~(40)Ca+~(208)Pb is investigated in the fully microscopic time-dependent Hartree-Fock(TDHF) theory. The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions, in which the full Skyrme energy functional SLy4d and SLy5 are adopted.We study the energy dependence of capture cross sections, and find that the experimental data are well reproduced by the TDHF calculations. Both fusion and quasifission events are observed in the reaction ~(40)Ca+~(208)Pb. The contact time, mass and charge of quasifission fragments show a wide distribution in SLy4d compared with SLy5, implying that more nucleons are transferred in the SLy4d calculations. We find that the total kinetic energy of quasifission fragments in the TDHF calculations is distributed around Viola systematics, indicating that most of the relative kinetic energy is dissipated in quasifission dynamics.     

25MeV/u 40)Ar+209Bi裂变反应研究

实验对25MeV/u ⁴⁰Ar+²⁰⁹Bi体系的裂变反应,利用线性动量转移的分窗选择不同的激发能,研究裂变动能分布和质量分布与热核初始激发能的关系.实验证实激发能小于380MeV时裂变总动能分布与低激发能复合核相似.激发能大于380MeV时,最可几动能呈现出随激发增加而增加,并出现高能非对称性,而且质量分布宽度随激发能增加而迅速增大.     

30MeV/u 40Ar+58,64Ni、115In反应中IMF的元素分布

在5°—140°范围内测量了30MeV/u40Ar束流轰击不同靶核(58Ni、64Ni、115In)时出射的中等质量碎片的元素分布.在20°—80°之间,观察到了原子序数大于弹核原子库数的出射碎片(Z=3—24),发现中等质量碎片的微分截面在其原子库数从小于弹核原子库数向大于弹核原子库数变化过程中是连续变化的,该角区出就碎片的元素分布与弹核原子库数关系不大.对中能区核反应的过渡性质做了讨论,指出了探测阈对所测得的元素分布的影响,并讨论了元素分布的幂指数规律.     

Significantly Improving the Escape Time of a Single ~(40)Ca~+ Ion in a Linear Paul Trap by Fast Switching of the Endcap Voltage

Sympathetic cooling is a method used to lower the kinetic energy of ions with complicated energy-level structures,via Coulomb interactions with laser-cooled ions in an ion trap.The ion to be sympathetically cooled is sometimes prepared outside of the trap,and it is critical to introduce this ion into the trap by temporarily lowering the potential of one endcap without allowing the coolant ion to escape.We study the time required for a laser-cooled ion to escape from a linear Paul trap when the v...     

High-lying excited states in ~(10)Be from the ~9Be(~9Be,~(10)Be)~8Be reaction

A transfer-reaction experiment of ~9Be(~9Be,~(10)Be)~8Be was performed at a beam energy of 45 Me V.Excited states in ~(10)Be up to 18.80 Me V are produced using missing mass and invariant mass methods.Most of the observed high-lying resonant states,reconstructed from theα+~6He and t+~7Li decay channels,agree with the previously reported results.In addition,two new resonances at 15.6 and 18.8 Me V are identified from the present measurement.The 18.55 Me V state is found to decay into both the t + ~7Lig:s: and t + ~7Li?(0.478 MeV) channels, with a relative branching ratio of 0:93 ± 0:33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.     

30MeV/u 40Ar+58,64Ni和115In反应中中等质量碎片的角分布

在5°—140°范围内测量了30MeV/u ⁴⁰Ar束流轰击不同靶核(⁵⁸Ni、⁶⁴Ni、¹¹⁵In)后出射的中等质量碎片(IMF,Z=3—19)的角分布.用指数分布函数dσ/dΩ=N·exp(–θ/α)对出射碎片角分布分角区做了拟合.对3个反应系统分别提取出与相互作用时间有关的衰减因子α和与发射源强度有关的物理量N,讨论了α与N在不同角区与反应系统和出射IMF电荷数的关系.考察了角分布与同位旋自由度和反应系统对称性的关系.     

30MeV/u 40Ar+natAg反应中中等质量碎片的发射源

在6°─110°范围内测量了30MeV/u的⁴⁰Ar轰击^natAg靶产生的中等质量碎片(3≤Z≤16)能谱,利用运动源模型拟合能谱,并详细讨论了类弹、类靶和中速这三种源的特性及其随角度和中等质量碎片电荷的变化规律.从前角区中等质量碎片的符合测量中得到关联测得的两个中等质量碎片分别来自于两个发射源,即一个来自于类弹源,另一个来自于中速源的几率占绝大多数.     

Simulation of the fission dynamics of the excited compound nuclei ~(206)Po and ~(168)Yb produced in the reactions ~(12)C+~(194)Pt and ~(18)O+~(150)Sm

A two-dimensional dynamical model based on the Langevin equation was used to study the fission dynamics of the compound nuclei ~(206)Po and ~(168)Yb produced in the reactions ~(12)C+~(194)Pt and ~(18)O+~(150)Sm,respectively.The fission cross section and average pre-scission neutron multiplicity were calculated for the compound nuclei ~(206)Po and ~(168)Yb,and results of the calculations compared with the experimental data.The elongation coordinate was used as the first dimension and the projection of the total spin of the compound nucleus onto the symmetry axis,K,considered as the second dimension in the Langevin dynamical calculations.In the two-dimensional calculations,a constant dissipation coefficient of K and a non-constant dissipation coefficient have been used to reproduce the abovementioned experimental data.It is shown that the two-dimensional Langevin equation can satisfactorily reproduce the fission cross section and average pre-scission neutron multiplicity for the compound nuclei ~(206)Po and ~(168)Yb by using constant values of the dissipation coefficient of K equal to γκ=0.18(MeV zs)~(-1/2) and γκ= 0.20(MeV zs)~(-1/2)for the compound nuclei ~(206)Po and ~(168)Yb,respectively.     

Tm3+离子在钨酸锌单晶中的光谱特征

采用丘克拉斯基法生长出一系列ZnWO4:Tm3 单晶 ,Tm3 浓度x =0 1 ,0 3,0 5 ,0 7和 1 0mol%。用 80 7nmLD激发 ,观察到 4 86和 6 95nm的上转换发光 ,分别相应于 1 G4→ 3 H6和3 F3 → 3 H6的跃迁 ,发光强度与泵浦光功率成双对数关系 ,其指数分别为 0 8和 1 1次方关系。     

Pairwise Interactions of Fe3+ Ions in InBO3 Crystals

Measurements of the electron paramagnetic resonance (EPR) of Fe³⁺ ion pairs in InBO₃ crystals are conducted. Some parts of the procedure of spectrum identification without measuring the temperature dependence of the resonant line intensities have been developed. Experimental curves of the second- and fourth-order axial Hamiltonian constants D _S and (a – F)_S, respectively, of the total spin number S are constructed. The single-ion second-order axial constant D _c is well described by a linear dependence on S. The constant (a – F)_S has a quadratic dependence.     

Fragment distribution in ~(78,86)Kr+~(181)Ta reactions

Within the framework of the isospin-dependent quantum molecular dynamics model, along with the GEMINI model, the ~(86)Kr+~(181)Ta reaction at 80, 120 and 160 MeV/nucleon and the ~(78)Kr+~(181)Ta reaction at 160 MeV/nucleon are studied, and the production cross sections of the generated fragments are calculated. More intermediate and large mass fragments can be produced in the reactions with a large range of impact parameter. The production cross sections of nuclei such as the isotopes of Si and P generally decrease with increasing incident energy.Isotopes near the neutron drip line are produced more in the neutron-rich system ~(86)Kr+~(181)Ta.     

EPR and Optical Absorption Study of VO2+ Ions Doped Potassium Hexaaquazinc (II) Sulfate Single Crystals

X-band single-crystal electron paramagnetic resonance (EPR) studies are done on VO²⁺ ions doped in potassium hexaaquazinc (II) sulfate, K₂[Zn (H₂O)₆] (SO₄)₂ (PHZS) at room temperature. The spin Hamiltonian parameters, i.e., g and A tensors and their direction cosines, are evaluated by the standard diagonalization procedure using angular variation of the EPR spectra in three planes (ab, bc* and c*a), with the help of a computer program. The EPR spectrum is simulated using the EasySpin program to verify the calculations. The detailed EPR analysis indicates the presence of two magnetically inequivalent VO²⁺ sites. Both the vanadyl complexes are found to take up the substitutional position in the host lattice. The optical absorption spectrum of VO²⁺ ions doped in PHZS single crystal at room temperature is also recorded and four main d–d transfer bands in the visible region are assigned. The theoretical band positions are obtained using energy expressions and a good agreement is found with the experimental values. With the help of assigned bands the crystal-field parameters (Dq, Ds and Dt) are evaluated. Finally, with the optical and EPR data, the nature of bonding in the complex is discussed.     

An Investigation of ~4He+~(12)C and ~4He+~(16)O Reactions Using the Cluster Model

The α-target semimicroscopic single folding potentials have been derived by folding a composite (repul-sive and attractive) effective α-α interaction with the α-cluster distribution density in the target nuclei. The obtained potentials are considered as the real part of the nuclear optical model potentials, while the imaginary parts are phe-nomenologicaly expressed using the Woods-Saxon form. Nine sets of measured experimental data of the 4He+12C and 4 He+16O elastic rainbow scattering over the energy range 80-240 MeV are analyzed using the obtained potentials. The data are successfully reproduced using the extracted potentials. The resulted reaction cross sections are also investigated and compared with the available corresponding data.     

Bremsstrahlung neutrino energy loss for ~(24)Mg,~(28)Si,~(32)S,~(40)Ca,~(56)Fe in strong electron screening

Based on Weinberg-Salam theory the bremsstrahlung neutrino energy loss for nuclei 24Mg,28Si,32S,40Ca and 56Fe are investigated in strong electron screening.Our results are compared with those of Dicus' and show that the latter are higher by 2 orders of magnitude in the density-temperature region of 108 g/cm3 ρ/μe 1011 g/cm3 and 2.5 T9 4.5.On the other hand,the factor C shows that the maximum differences are 99.16%,99.13%,99.12%,99.055%,99.040% corresponding to the nuclei 24Mg,28Si,32S,40Ca and 56Fe.     

Bremsstrahlung neutrino energy loss for ~(24)Mg, ~(28)Si, ~(32)S, ~(40)Ca, ~(56)Fe in strong electron screening

Based on WeinbergoSalam theory the bremsstrahlung neutrino energy loss for nuclei ~(24)Mg, ~(28)Si, ~(32)S, ~(40)Ca and ~(56)Fe are investigated in strong electron screening. Our results are compared with those of Dicus' and show that the latter are higher by 2 orders of magnitude in the density-temperature region of 10~8 g/cm~3 ≤ρ/μ_e≤10~(11) g/cm~3 and 2.5 ≤ T_9 ≤4.5. On the other hand, the factor C shows that the maximum differences are 99.16%, 99.13%, 99.12%, 99.055%, 99.040% corresponding to the nuclei ~(24)Mg, ~(28)Si, ~(32)S, ~(40)Ca and ~(56)Fe.