The 7 Li + ion is one of the most important candidates for verifying QED theory and obtaining the precise value of the fine-structure constant α. 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 7 Li + ions to few mK using 40 Ca + ions in a linear Paul trap. A mixed ion crystal of 40 Ca + ions and 7 Li + ions are obtained. We also analyze the motion frequency spectra of pure 40 Ca + ions and mixed ions.
The 7 Li + ion is one of the most important candidates for verifying QED theory and obtaining the precise value of the fine-structure constant α. 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 7 Li + ions to few mK using 40 Ca + ions in a linear Paul trap. A mixed ion crystal of 40 Ca + ions and 7 Li + ions are obtained. We also analyze the motion frequency spectra of pure 40 Ca + ions and mixed ions.
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 167nm 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 Doppler-cooled 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 7 mK 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.
Coulomb crystals, containing up to a few hundred ions of which more than 50% were cooled sympathetically by the Coulomb interaction with laser cooled Mg+ ions, have been produced in a linear Paul trap. By controlling the balance of the radiation pressure from the two cooling lasers, the Coulomb crystals could be segregated according to ion species. Previous studies of ion crystals and molecular dynamics simulations suggest that the temperature may be around 10 mK or lower. The obtained results indicate that a wide range of atomic and molecular ions, which due to their internal structures are not amenable to direct laser cooling, can be effectively cooled and localized (crystallized) in linear Paul traps. For high resolution spectroscopy of such ions this may turn out to be very useful.
We report on the sympathetic cooling and Coulomb crystallization of xenon highly charged ions (HCIs) with laser-cooled Ca+ ions. The HCIs are produced in a compact electron beam ion trap, then charge selected, decelerated, and finally injected into a cryogenic linear Paul trap. There, they are captured into 40Ca+ Coulomb crystals, and co-crystallized within them, causing dark voids in their fluorescence images. Fine control over the number of trapped ions and HCIs allows us to realize mixed-species crystals with arbitrary ordering patterns. By investigating Xeq+--Ca+ strings, we confirm the HCI charge states, measure their lifetime and characterize the mixed-species motional modes. Our system effectively combines the established quantum control toolbox for Ca+ with the rich set of atomic properties of Xe highly charged ions, providing a resourceful platform for optical frequency metrology, searches for signatures of new physics, and quantum information science.
We have created multispecies Coulomb crystals in a linear Paul trap containing up to a few hundred ions of which more than 50 were cooled only sympathetically through the Coulomb interaction with laser-cooled Mg+ ions. In an extreme case, one laser-cooled ion maintained order in a 15 ion string. Ion species segregation was obtained by radiation pressure. Previous experiments and molecular dynamics simulations suggest the temperature is 10 mK or lower. These results indicate that a wide range of atomic and molecular ions can be cooled and localized in linear Paul traps which is important for improvements in spectroscopic studies of such ions.
We report the sympathetic cooling and Coulomb crystallization of xenon highly charged ions (HCIs) with laser-cooled Ca+ ions. The HCIs are produced in a compact electron beam ion trap, then charge selected, decelerated, and finally injected into a cryogenic linear Paul trap. There, they are captured into 40 Ca+ Coulomb crystals, and cocrystallized within them, causing dark voids in their fluorescence images. Fine control over the number of trapped ions and HCIs allows us to realize mixed-species crystals with arbitrary ordering patterns. By investigating Xeq+ − Ca+ strings, we confirm the HCI charge states, measure their lifetime, and characterize the mixed-species motional modes. Our system effectively combines the established quantum control toolbox for Ca+ with the rich set of atomic properties of Xe highly charged ions, providing a resourceful platform for optical frequency metrology, searches for signatures of new physics, and quantum information science.
Sympathetic cooling of 113Cd+ by laser-cooled 40Ca+ in a linear Paul trap for Microwave Ion Clocks
We report sympathetic cooling of 113Cd+ by laser-cooled 40Ca+ in a linear Paul trap for microwave clocks. Long-term low-temperature confinement of 113Cd+ ions was achieved. The temperature of these ions was measured at 90(10) mK, and the corresponding uncertainty arising from the second-order Doppler shifts was estimated to a level of 2×10−17. Up to 4.2×105 Cd+ ions were confined in the trap, and the confinement time constant was measured to be 84 hours. After three hours of confinement, there were still 105 Cd+ ions present, indicating that this Ca+--Cd+ dual ion system is surprisingly stable. The ac Stark shift was induced by the Ca+ lasers and fluorescence, which was carefully estimated to an accuracy of 5.4(0.5)×10−17 using a high-accuracy \textit{ab initio} approach. The Dick-effect-limited Allan deviation was also deduced because deadtimes were shorter. These results indicate that a microwave clock based on this sympathetic cooling scheme holds promise in providing ultra-high frequency accuracy and stability.