Li Jiaomei

Experimental Determination (similar to mHz) of the Ground-State Hyperfine Separation of Trapped Hg-199(+) in a Hyperbolic Paul Trap

The Ramsey fringes on the ground-state hyperfine transition of Hg-199(+) (Delta F = 1, Delta m(F) = 0) ions trapped in a hyperbolic Paul trap are firstly observed with the method of time-separated oscillatory fields. The full width at half maximum of central Ramsey fringes is about 25mHz and the corresponding quality factor Q of the line is greater than 10(12) for the trapped Hg-199(+) microwave frequency standard. The hyperfine transition frequency shifted by magnetic field is also measured by the high-resolution Ramsey fringes. The final result is Delta nu(hfs) = 40507347997.3(0.5) Hz, which is corrected to zero magnetic field.

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.

Microwave-Optical Double-Resonance Spectroscopy Experiment of 199Hg+ Ground State Hyperfine Splitting in a Linear Ion Trap

We report a spectroscopy experiment of the Hg-199(+) ground state hyperfine splitting in a linear ion trap. The ions are optically pumped by a discharge lamp and cooled by helium buffer gas. The ground state hyperfine splitting is measured to be 40507347996.8(0.1) Hz by the microwave-optical double-resonance method. A narrow line width as 30 mHz is also observed. This progress builds the foundation for the realization of trapped Hg-199(+) ion frequency standards.

Comparison experiments of neon and helium buffer gases cooling in trapped Hg-199(+) ions linear trap

The influences of different buffer gas, neon and helium, on Hg-199(+) clock transition are compared in trapped Hg-199(+) linear trap. By the technique of time domains Ramsey separated oscillatory fields, the buffer gas pressure frequency shifts of Hg-199(+) clock transition are measured to be (df/dP(Ne)) (1/f) = 1.8 x 10(-8) Torr(-1) for neon and (df/dP(He)) (1/f) = 9.1 x 10 8 Torr(-1) for helium. Meanwhile, the line-width of Hg-199(+) clock transition spectrum with the buffer gas neon is narrower than that with helium at the same pressure. These experimental results show that neon is a more suitable buffer gas than helium in Hg-199(+) ions microwave frequency standards because of the Hg-199(+) clock transition is less sensitive to neon variations and the better cooling effect of neon. The optimum operating pressure for neon is found to be about 1.0 x 10(-5) Torr in our linear ion trap system.

Control of a Cloud of Laser-Cooled 40Ca+ in a Linear Ion Trap

A cloud of laser-cooled 40Ca+ is successfully trapped and manipulated under well control in our home-built linear ion trap, which is designed and constructed solely for studying quantum information processing. By exploring the variation of the ion cloud with respect to the trap parameters, we have optimized the trapping condition and obtained very good fluorescence spectra. We observe the dynamics of the ion cloud, and estimate the temperature of the ion cloud to be of the order of milli-Kelvin.

Fluorescence Detection and Buffer Gas Cooling of Trapped Mercury Ions in Paul Trap

Hg ions are confined in a hyperboloid ion trap. With the rf discharge Hg-202 isotope lamp, the fluorescence signal of trapped Hg ions is observed. By means of buffer gas cooling, the ionic temperature is reduced. As a result, the trapping time is increased and the signal-to-noise ratio (SNR) of the fluorescent signal is improved. The temperature of ion cloud is estimated by measuring the space charge shift.

A Method of Measuring the Axial Secular Motion Temperature of Trapping Large Size Ion Clouds

A large cloud of Ca-40(+) is successfully trapped and manipulated in a linear ion trap. The axial length of the ion cloud is measured under a series of end-cap voltages. We propose a method of measuring the axial secular motion temperature of the ion cloud by analyzing its image on an electron-multiplying CCD. The method is based on the Boltzmann equation that the axial density distribution of ions at secular motion temperature T satisfies. The axial secular motion temperature of the ion cloud is also obtained by measuring the Doppler broadened line width. For the same trapping parameters, the axial secular motion temperature by analyzing the image of ion cloud is 840 K and by fitting the experimental resonance line profile is 700 K.

Kinetic Energy of Trapped Ions Cooled by Buffer Gas

The average kinetic energy of Ca-40(+) ions is measured by the method of evaporating ions in an rf ion trap. The kinetic energy of the ion Ca-40(+) varies from 0.5 eV to 0.2 eV with changing buffer gas pressure from 10(-7) mbar to 10(-5) mbar. The Brownian motion model is also introduced to calculate the average kinetic energy of the trapped ions.

Detection of isotopes of mercury ions by resonant ejection in Paul trap

A simple method to detect mercury ions confined in a Paul trap has been developed by resonant ejection. In this method, frequency of the additional ejection ac voltage is scanned instead of the amplitude of the if drive voltage in conventional methods. It is possible not only to observe the spectra of the secular oscillation of the trapped ions directly, but also to eject the confined ions from the trap mass-selectively.

Charge transfer for reactions of Sc3+ with N-2 and H-2 at electron-volt energy

The charge transfer rate coefficients for reactions of SC3+ with N-2 and H-2 have been measured at the mean collision energy of 4.2 eV. The rate coefficients are derived from the decay rate of ion signals by using ion storage in a radio frequency ion trap. The rate coefficients are 8.18(0.18) x 10(-10)cm(3.)s(-1) at T-equiv x 1.26 x 10(4) K for SC3+ with N-2 and 1.44(0.39) x 10(-9)cm(3.)s(-1) at T-equiv approximate to 1.67 x 10(3) K for Sc3+ with H-2, respectively. Both results are comparable with the Langevin rate coefficients.