Ph.D. Thesis - Physics

Chapter 6
Surface-electrode PCB ion traps
for trap development
In Ch. 4, we explained how proposals for analog ion-trap quantum simulation of spin frustra-
tion rely upon a 2-D lattice of potentials. However, as reported in Ch. 5, we discovered that
the interactions between ions held in individual potential wells are quite weak, for a given
ion-ion distance, when compared to other designs (e.g. linear ion traps). This motivates us
to design ion traps that can confine a 2-D array of trapped ions all in the same potential
well. In order to design and test such a trap, we have chosen to use printed circuit board
(PCB) ion trap technology. These traps are relatively simple to design and manufacture,
and can be used to measure all the basic properties of a trap, as was done without the use
of PCB’s in Ch. 5. The large (∼ 100 µm) minimum feature size of PCB’s prevents scaling
to a “microfabricated” scale trap, should the need arise. Nevertheless, we find them to be
a useful tool for trap design and basic testing.
In this chapter, we explore some basic questions regarding the loading of ions into such
a trap. With PCB’s, the presence of dielectrics in between the trap electrodes presents the
problem of stray charge buildup. When using the conventional technique of electron impact
ionization, we must ask ourselves how much this trapped charge affects the trap potentials,
and even if, in extreme cases, it could prevent trapping at all. We also ask the question
of how these effects might be mitigated. In the course of this work, we solve this problem
in two ways, first by removing as much dielectric as possible from the trap structure, and
then by using a helium buffer gas to cool the ion clouds that suffer greatly from rf heating
in the presence of stray fields. We explore whether it’s possible, via this technique, to trap
a laser-cooled sample of ions at UHV pressures, even in the presence of large stray fields.
In the second experiment presented in this chapter, we study direct laser ablation of
ions into surface-electrode traps. In so doing, we again address issues of charge buildup,
but the emphasis is on the low trap depths of surface-electrode traps. We ask the question
of how shallow a trap may be loaded with this method, and how that result compares to
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