Bright source of cold ions for surface-electrode traps

We produce large numbers of low-energy ions by photoionization of laser-cooled atoms inside a surface-electrode-based Paul trap. The isotope-selective trap’s loading rate of $4\times {10}^5{\mathrm{Yb}}^{+}\mathrm{ions}∕\mathrm{s}$ exceeds that attained by photoionization (electron-impact ionization) of an atomic beam by three (six) orders of magnitude. Traps as shallow as $0.13\mathrm{eV}$ are easily loaded with this technique. The ions are confined in the same spatial region as the laser-cooled atoms, which will allow the experimental investigation of interactions between cold ions and cold atoms or Bose-Einstein condensates.

Figure 1

Setup for loading a surface-electrode ion trap by in-trap photoionization of laser-cooled atoms. A ${}^{172}\mathrm{Yb}$ or ${}^{174}\mathrm{Yb}$ magneto-optical trap (MOT) is formed $4\mathrm{mm}$ above the trap surface. Cold ${\mathrm{Yb}}^{+}$ ions are produced inside the Paul trap by single-photon excitation from the excited ${}^1{P}_1$ atomic state.

Figure 2

(Color online) Left: Trapping pseudopotential for rf amplitudes of $V_o=540$ V and $V_c=-340\mathrm{V}$ applied to the outer and center electrodes together with a dc bias of $-1.25\mathrm{V}$ applied to all electrodes. The contours are spaced by $50\mathrm{meV}$. Right: The dc-unbiased trap (dashed blue curve) exhibits less micromotion heating but is significantly shallower than the dc-biased trap (solid red curve).

Figure 3

Linear dependence of the loss rate constant of a ${}^{174}\mathrm{Yb}$ MOT (rms width of $300\mathrm{\mu }\mathrm{m}$) on $370\mathrm{nm}$ beam peak intensity $(w=43\mathrm{\mu }\mathrm{m})$, indicating that photoionization is accomplished with a single $370\mathrm{nm}$ photon from the ${}^1{P}_1$ state that is populated during laser cooling with $399\mathrm{nm}$ light.

Figure 4

(Color online) Number of trapped ${}^{172}\mathrm{Yb}$ ions for photoionization loading with the uv LED from an atomic beam (black squares), with a uv LED from a MOT (red circles), and from a MOT with both uv LED and a $370\mathrm{nm}$ laser (blue triangles). The fitted rates are $R=200$, $1.4\times {10}^5$, and $3.8\times {10}^5{\mathrm{s}}^{-1}$, respectively.

Figure 5

(Color online) Spatially overlapping ion and atom clouds. The false color image shows a trapped ${}^{172}{\mathrm{Yb}}^{+}$ ensemble containing ${10}^2–{10}^3$ ions (blue cloud, lower left), placed inside a magneto-optical trap containing $5\times {10}^5$ neutral ${}^{172}\mathrm{Yb}$ atoms (red cloud, upper right). The solid and dashed lines indicate the half-maximum contour for the ions and atoms, respectively.