State-Selective Quantum Interference Observed in the Recombination of Highly Charged ${\mathrm{Hg}}^{75+\cdots 78+}$ Mercury Ions in an Electron Beam Ion Trap

We present experimental data on the state-selective quantum interference between different pathways of photorecombination, namely, radiative and dielectronic recombination, in the $KLL$ resonances of highly charged mercury ions. The interference, observed for well resolved electronic states in the Heidelberg electron beam ion trap, manifests itself in the asymmetry of line shapes, characterized by “Fano factors,” which have been determined with unprecedented precision, as well as their excitation energies, for several strong dielectronic resonances.

Figure 1

Two different pathways for the ionization process are shown on the left side of the figure corresponding to the direct photoionization (DPI) and the indirect photoionization (IPI). The picture on the right side illustrates the time-reversed RR and DR processes.

Figure 2

Logarithmic 2D contour plot of the $KLL$ resonances for highly charged mercury ions. The diagonal bands correspond to RR processes into $J=1/2$ (upper) and $J=3/2$ (lower). DR processes are visible as single bright spots. The areas 1 thru 4 (outlined in white) in the upper RR band for $J=1/2$ indicate thin cuts, whose projection onto the electron beam axis is shown in Figs. 3, 4.

Figure 3

Experimental (black curve) and fitted (red curve) data for two different slices of the RR $n=2$, $J=1/2$ in the $K{L}_{12}{L}_{12}$ region whose analysis shows negative Fano factors in comparison with a normalized nonconvoluted theoretical cross section (blue and green curves). Left: Projection of the upper slice where He- and Li-like ions are observed. Right: Projection of an intermediate region showing Be- and Li-like resonances.

Figure 4

In comparison with the He- and Li-like resonances in the $K{L}_{12}{L}_{12}$ region (see Fig. 3) the $K{L}_{12}{L}_3$ Be- and B-like ones show opposite, i.e., positive Fano factors. The two cuts displayed here exemplify the method used to resolve resonances from specific charge states. In these pictures are also shown the normalized nonconvoluted theoretical cross section (blue and green curves).