Ph.D. Thesis - Physics

Figure 6-12: Measured pickup from the rf electrode during laser ablation. The rf begins
recovering after about 15 µs, and during this time ions are trapped. Figure reproduced
from Ref. [HMO + 06].
lowered, some ions enter the trap, which returns to full strength with some ions already
inside it. This was first observed by Hashimoto et al. [HMO + 06], and the relevant plot from
that paper is presented in Fig. 6-12. The loading of ions into a conservative trap potential
requires a nonconservative step; normally, it is the conversion of neutral atoms into ions
within the trap, but with ablation loading it is an induced time-dependence of the trapping
potentials themselves. We note also that lower-energy ablation pulses have been used in lieu
of an oven to produce neutral atoms that are then photoionized within the trap [HGH + 07].
Laser ablation has a number of possible advantages. For one, it requires only a single
laser, and the process is not sensitive to its frequency. For instance, if one wished to load
simultaneously atomic and molecular ions, an ablation pulse (or set of synchronized ablation
pulses) might do the trick. As with e-gun loading, however, the lack of isotopic selection
could potentially lead to unwanted trapped species. Second, it is very fast: carefully-
calibrated ablation loading could thus be very useful for loading the many ions needed in
a scalable quantum simulator. If an ion was lost during a simulation, one could envision
a classical subroutine that pauses execution of the algorithm and then reloads an ion in
the correct spot using a single ablation pulse. The ion could be trapped and re-cooled
in much less than one second. Third, ablation loading does not create a large heat load.
In a cryogenic environment, the heat generated by a resistive oven could be conducted to
the trap electrodes, increasing decoherence rates. In our later work, we solve this problem
by placing the oven in contact with the 40 K radiation shield, which has enough cooling
power to handle the heat load. In the future, however, it may be advantageous to have very
site-specific loading, as in the scenario described above. In this case, ablation loading may
be a superb option.
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