Guan Hua

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

Precision measurement of the 4s(2)S(1/2)-3d(2)D(5/2) clock transition based on Ca-40(+) ion at 729 nm is reported. A single Ca-40(+) 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 x 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 411 042 129 776 393.0(1.6) Hz with the correction of the systematic shifts. In order to carry out the comparison of two Ca-40(+) optical frequency standards, another similar Ca-40(+) optical frequency standard is constructed. Two optical frequency standards exhibit stabilities of 1 x 10(-14) tau(-1/2) with 3 days of averaging. Moreover, two additional precision measurements based on the single trapped Ca-40(+) ion are carried out. One is the 3d(2)D(5/2) state 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 4s(2)S(1/2)-3d(2)D(5/2) clock transition; lambda(vertical bar mj vertical bar =1/2) = 395.7992(7) nm and lambda(vertical bar mj vertical bar =3/2) = 395.7990 (7) nm are reported, and it is the first time that two magic wavelengths for the Ca-40(+) clock-transition have been reported.

A Single Laser Cooled Trapped 40Ca+ Ion in a Miniature Paul Trap

We have observed the phenomenon of phase transition of a few trapped ions in a miniature Paul trap. Judging from the quantum jump signals, a single laser-cooled trapped Ca+ ion has been realized. The ion temperature is estimated to be 22mK. The result shows that the amplitude of ion micromotion is strongly dependent on the rf voltage.

Frequency Measurement of the Electric Quadrupole Transition in a Single Laser-Cooled (40)Ca(+)

The optical frequency of the 4s(2)S(1/2)-3d(2)D(5/2) transition in a single trapped and laser-cooled Ca-40(+) ion is measured with an optical frequency comb system referenced to a hydrogen maser. A 729-nm laser can be locked to the clock transition about ten hours and the Allan deviation is better than 2 x 10(-14)/1000s.

Measurement of Secular Motion Frequency in Miniature Paul Trap to Ascertain the Stability Parameters

(40)Ca(+) ions are trapped and laser cooled in a miniature Paul trap. The secular motion was observed by the radio-frequency resonance of the ion cloud and Zeeman profile sidebands of a single ion experimentally. The trap stability parameters.. and.. are determined with an uncertainty under 1% by the secular motion frequency measurement. The trap efficiency is 0.75. A practicable suggestion is given for the benefits of a new trap design.

Experimental Improvement of Signal of a Single Laser-Cooled Trapped 40Ca+ Ion

A single 40Ca+ ion is loaded in a miniature Paul trap and the probability of directly loading a single ion is above 50%. The signal-to-noise ratio and the storage time for a single ion have been improved by minimizing the ion micromotion and locking a 397 nm cooling laser to a Fabry–Perot interferometer and optogalvanic signal. From the fluorescence spectrum, the ion temperature is estimated to be about 5 mK.

The progress of the precision spectroscopywith single trapped and laser cooled 40 Ca + ion

The experimental study at Wuhan Institute of Physics and Mathematics (WIPM), Chinese Academy of Scienses (CAS) on the precision spetroscopy based on single trapped Ca+ ion is described in this paper. A single Ca+ ion is trapped in a miniature Paul trap and laser cooled to Lamb-Dicke regime, and the ion can be trapped more than 2 months. The linewidth of the 729 nm laser for probing the Ca+ 4 s 2 S 1/2-3 d 2 D 5/2 clock transition is reduced to lessthan 1 Hz by locked to a super cavity, and the 729 nm laser can be locked more than 1 month continuously. Two similar Ca + ion optical frequency standards are set up for frequency comparison. The systematic uncertainty is evaluated to be ´ 10−17 for both ftrquency standards. The frequency difference of two frequency standards is measured to be 3.0 (5.5) ´ 10−17 within 42 d. The Allan deviation for a single clock is measured to be 1×10−14 τ −1/2 with a 3-d-continuous comparison, the stability for a reaches 7 ´ 10−17 at an averaging time of 20000 s. Meanwhile, the absolute frequency of the Ca+ 4 s 2 S 1/2-3 d 2 D 5/2 clock transition is measured to be 411042129776401.7(1.1) Hz with respect to the SI second through the Global Positioning System (GPSx). The precision spectroscopy experiments are carried out based on the single Ca+ ion system. The magic wavelengths for the Ca+ optical frequency standardare measured to be λ | mj |=1/2=395.7992(7) nm and λ | mj |=3/2=395.7990(7) nm, which agrees with theoretical calculation made by Tang et al. The lifetime of the 3 d 2 D 5/2 is measured to be 1174(10) ms, which is agree with the experimental measurement made by University of Oxford and University of Innsbruck and the recent theoretical calculation made by Sahoo.

Preparation of Ultracold Li + Ions by Sympathetic Cooling in a Linear Paul Trap *

The Li-7(+) ion is one of the most important candidates for verifying QED theory and obtaining the precise value of the fine-structure constant alpha. However, direct laser cooling of trapped Li+ ions will lead to strong background fluorescence which will influence the spectrum detection. The sympathetic cooling technique is a good choice to solve the problem. In this work, we report sympathetic cooling of Li-7(+) ions to few mK using Ca-40(+) ions in a linear Paul trap. A mixed ion crystal of Ca-40(+) ions and Li-7(+) ions are obtained. We also analyze the motion frequency spectra of pure Ca-40(+) ions and mixed ions.

Correlation between the magic wavelengths and the polarization direction of the linearly polarized laser in the Ca+ optical clock*

The magic wavelengths for different Zeeman components are measured based on the Ca-40(+) optical clock. The dynamic dipole polarizability of a non-zero angular moment level has correlation with the polarization direction of the linearly polarized laser beam, and we show that the four hyperfine structure levels of 4s(1/2,m=+/-1/2) and 3d(5/2,m=+/-1/2) for Ca-40(+) have the same dynamic dipole polarizability at the magic wavelength and a certain polarization direction. In addition, the existence of a specific direction of polarization may provide a new idea for improving the precision of magic wavelength measurement in experiment.

Determination of ion quantity by using low-temperature ion density theory and molecular dynamics simulation

In this paper, we report a method by which the ion quantity is estimated rapidly with an accuracy of 4%. This finding is based on the low-temperature ion density theory and combined with the ion crystal size obtained from experiment with the precision of a micrometer. The method is objective, straightforward, and independent of the molecular dynamics (MD) simulation. The result can be used as the reference for the MD simulation, and the method can improve the reliability and precision of MD simulation. This method is very helpful for intensively studying ion crystal, such as phase transition, spatial configuration, temporal evolution, dynamic character, cooling efficiency, and the temperature limit of the ions.

Compensating for excess micromotion of ion crystals

A new method of compensating for the excess micromotion along two directions in three-dimensional Coulomb crystals is reported in this paper; this method is based on shape control and optical imaging of a Coulomb crystal in a sectioned linear ion trap. The characteristic parameters, such as the ion numbers, temperatures, and geometric factors of different ion crystals are extracted from the images and secular motion excitation spectra. The method of controlling the shape of the ion crystals can be used in cold ion experiments, such as sympathetically cooling, structural phase transitions, and selective-control of ions, etc.