Ion traps you never knew existed
One of the neat things about superconducting qubits is that new qubit types constantly pop up. You have the transmon, xmon, pokemon, fluxonium, quatronium, blochnium… I don’t know what these are, but they do sound high-tech!
Ion traps, on the other hand, are much less exciting. God gave us a dozen or so good qubits to play around with, and that’s it. They come with excellent coherence times, unless we screw things up, which we usually do. Every now and again someone pulls out a qubit you never knew existed (cadmium anyone?), but otherwise, it’s a classic selection of Be - Mg - Ca - Sr - Ba - Yb.
Unable to design their own qubits, trapped-ion physicists channel their creativity through trap design. While most (but not all) superconducting qubits reside on planar chips with some very particular stackup optimised for low noise, ion traps can be extremely dissimilar from each other.
To make matters worse, ion trap taxonomy is rather opaque. We don’t give our designs easy-to-remember names. Instead, an incoming graduate student is more usually confronted with overloaded vague terms (“2D trap”, “3D trap”), or unhelpful specific ones (“Dave’s trap”, “NIST’s original surface trap”).
It would be quite helpful to create a unified taxonomy of ion traps, but such undertaking is beyond the scope of this post (plus, it would have to come from Dave himself). Instead, to start you off on your own journey in trapped-ion quantum computing, here is a vaguely ordered incomplete collection of different types of ion traps. Each trap type comes with several names: some common, some questionable, and others outright made up.
Enjoy, and let me know if there are any more names you would describe these traps with!
The “good old days” trap
AKA: the “proper” Paul trap, hyperbolic-electrode ring trap
Quadrupole rod trap
AKA: linear Paul trap, “give me some cage rods and I’ll give you atoms” trap
Multipole rod trap
AKA: “I found a lot of cage rods at the back of the drawer” trap
“Innsbruck-style” blade trap
AKA: Innsbruck trap, blade trap, macro-trap
Cavity blade trap
Works like charm, if you can align it!
Ring trap
AKA: I’m-not-afraid-of-micromotion trap
Fiber-cavity ring trap
AKA: I’m-not-afraid-of-charges trap
Spinning-field trap
AKA: big-ass EDM trap
Conveyor belt trap
AKA: bucket-brigade trap Only for expert-level ion trappers.
Surface trap
AKA: Surface-electrode trap, SET, chip trap, planar trap
Fun fact: Surface traps were apparently first proposed by Harvard’s Mara Prentiss in a conversation with Dave Wineland.
HOA trap
AKA: Sandia trap, high-optical access trap, slotted trap, bow-tie trap.
It is controversial whether the HOA trap is a surface trap or not.
Microwave resonator surface trap
AKA: $\lambda/2$ trap, Oxford microwave trap
Integrated optics surface trap
Low-loss integrated optics trap
Not an HOA trap
I mean, why would anyone confuse the two?
2D array trap
AKA: Microtrap array.
Many throught this was the way to scale up quantum computers, until they tried.
2D linear array trap
AKA: bucket-brigate trap
2.5D trap
AKA: Surface trap with a hat to protect it from the wind enhance confinement, Infineon trap
PCB trap
Probably the most economical way to get started with ion trapping.
3D trap
AKA: Stacked-wafer trap, microfabricated 3D trap, microscopic 3D trap.
The name “3D trap” is confusing as hell, so we continue to use it to make the field less accessible.
Junction trap
Fiber trap
NB: there are no optical fibers in the fiber trap
Stylus trap
Large mirror trap
AKA: the real “high optical access” trap
The “QCCD introduction slide” trap
NB: this trap is still work in progress
Penning trap
Surface penning trap
Addeneum: traps suggested by readers
Ring surface trap
Suggested on Twitter by Ion Busters
Diffractive mirror trap
AKA: Integrated collection optics trap.
Suggested in the comments by Erik Streed.
Integrated detector traps
Inspired by Erik Streed’s comment. Shameful I forgot to include it in the original post!
