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arXiv:physics/0702122 · Physical Review A

Observation of single collisionally cooled trapped ions in a buffer gas

M. P. Green, Jesse Wodin, Ralph G. DeVoe, P. Fierlinger, B. Flatt, G. Gratta, Francisco LePort, M. Montero Díez, Russell G. Neilson, K. O’Sullivan, Andrea Pietro Pocar, Samuel J. Waldman, Douglas S. Leonard, A. Piepke, C. K. Hargrove, D. Sinclair, V. Strickland, W. Fairbank, K. Hall, B. Mong, M. K. Moe, J. Farine, D. Hallman, C.J. Virtue, E. Baussan, Y. Martin, Dominique Schenker, J.L. Vuilleumier, J.-M. Vuilleumier, P. Weber, M. Breidenbach, R. Conley, Carter Hall, J. Hodgson, D. Mackay, A. Odian, C.Y. Prescott, Peter C Rowson, Knut Skarpaas, K. Wamba

Published Aug 9, 2007• 33 citations
arXivHTMLPDF

Abstract

Individual Ba ions are trapped in a gas-filled linear ion trap and observed with a high signal-to-noise ratio by resonance fluorescence. Single-ion storage times of $\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{min}$ $(\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{min})$ are achieved using He (Ar) as a buffer gas at pressures in the range $8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}--4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}\text{torr}$. Trap dynamics in buffer gases are experimentally studied in the simple case of single ions. In particular, the cooling effects of light gases such as He and Ar and the destabilizing properties of heavier gases such as Xe are studied. A simple model is offered to explain the observed phenomenology.

DOI
10.1103/physreva.76.023404

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Individual Ba ions are trapped in a gas-filled linear ion trap and observed with a high signal-to-noise ratio by resonance fluorescence. Single-ion storage times of \ensuremath∼5min\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{min}\ensuremath∼5min (\ensuremath∼1min)(\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{min})(\ensuremath∼1min) are achieved using He (Ar) as a buffer gas at pressures in the range 8\ifmmode×\else\texttimes\fi10\ensuremath−5−−4\ifmmode×\else\texttimes\fi10\ensuremath−3torr8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}--4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0.3em}{0ex}}\text{torr}8\ifmmode×\else\texttimes\fi10\ensuremath−5−−4\ifmmode×\else\texttimes\fi10\ensuremath−3torr. Trap dynamics in buffer gases are experimentally studied in the simple case of single ions. In particular, the cooling effects of light gases such as He and Ar and the destabilizing properties of heavier gases such as Xe are studied. A simple model is offered to explain the observed phenomenology.
The modification of ion production efficiency via resonant laser-driven ionisation in the presence of high buffer gas atmospheres has been experimentally investigated in a barium vapour. The populations of several energy levels of neutral and singly ionised Ba were measured as a function of both helium and argon pressures by the time-resolved hook technique. The behaviours of He and Ar are quite distinct. The percentage of ionisation decreased monotonically from nearly 100% to less than 10% as the helium pressure was increased from 0.01 to 1 atm, while no quenching was observed in 1 atm of Ar. These observations are consistent with a quenching mechanism based in part on cooling of the 'hot' electrons through momentum-changing elastic collisions with the He atoms.
We provide a comprehensive theoretical framework for describing the dynamics of a single trapped ion interacting with a neutral buffer gas, thus extending our previous studies on buffer-gas cooling of ions beyond the critical mass ratio [B. H\"oltkemeier et al., Phys. Rev. Lett. 116, 233003 (2016)]. By transforming the collisional processes into a frame, where the ion's micromotion is assigned to the buffer-gas atoms, our model allows us to investigate the influence of nonhomogeneous buffer-gas configurations as well as higher multipole orders of the radio-frequency trap in great detail. Depending on the neutral-to-ion mass ratio, three regimes of sympathetic cooling are identified which are characterized by the form of the ion's energy distribution in equilibrium. We provide analytic expressions and numerical simulations of the ion's energy distribution, spatial profile, and cooling rates for these different regimes. Based on these findings, a method for actively decreasing the ion's energy by reducing the spatial expansion of the buffer gas arises (forced sympathetic cooling).
Following the previous study with an extensive range of quantum calculations involving different electronic states of the BN- anion [Dulitz et al., Phys. Scripta 100, 055411 (2025)], we now extend that work by modeling the quantum dynamics of the collision cooling of its rotational states in order to investigate possible paths for bringing this molecular anion down to temperatures of a few Kelvins. This specific ionic system is of direct interest when modeling experiments in cold ion traps where He or Ar atoms can function as the chief buffer gases that drive the anions down to the low trap temperatures. We employ accurate, ab initio calculations of the potential energy surfaces for the title system in its ground electronic state, interacting with either He or Ar atoms. We then obtain a wide range of inelastic cross sections and the ensuing rate coefficients in order to model the quantum kinetics of the time evolution of the cooling steps under different temperature and trap conditions. The results are analyzed and employed to estimate the cooling efficiency paths provided by various trap arrangements for the title anion. The results show that-using either of the two investigated species-the buffer gas cooling process very efficiently brings the anions to their lowest rotational states. These findings are very promising for future applications in the field of anion laser cooling.
Buffer gas cooling is the most effective and practical method to cool ions in ion trap.The kind and quantity of buffer gas are the key technologies in mercury ion microwave frequency standard experiments.Buffer gas made of helium,neon or argon was studied to cool trapped mercury ions(~(199)Hg~+) in a linear ion trap by introducing a resistance term in Mathieu's equation.It's found that the decay time of motion of ~(199)Hg~+ in argon gas is the shortest,and the frequency shift of the clock transition(40.5 GHz) is minimum when the pressure of helium is 10~(-5) Torr or the pressure of neon gas is 2.4×10~(-5) Torr.Neon is the most suitable buffer gas among helium,neon and argon,considering the decay time-constant of motion of ~(199)Hg~+ in buffer gases and ~(199)Hg~+ clock transition shift's sensitivity to the change of the pressure of buffer gas.