What is the advantage of segmented particle traps? I'm currently trying to familiarize myself with the physics of ion and particle traps, especially with linear Paul traps. Many scientific experiments I've come across use segmented electrodes (like in this image from a Nature article). My question is what do you gain by segmenting the electrodes? I could imagine that you can move the trapped particles along the axis to some extent, or determine their position in the trap. But in both cases I believe there are more precise methods.
 A: In the recent ion trap designs much of the emphasis is on traps that can store ions in multiple trapping zones and transport ions between them. This is crucial for the ion trap realizations of a quantum computer with many ions (qubits). In the ion traps that are intended to be used for quantum information processing, we need to transport single and multiple ions, take a pair of ions in a single zone and separate them into independent zones, or combine two zones, without excess heating.
These multiple segments are used to create multizone traps. Also by applying appropriate potential to the segments it is possible to move the potential well and carry the ions within it. This is done using segments that are called control electrodes, which are intended to shuttle ions from a zone to another, merge two zones and split one into separate zones. For, example, this is how storing in multiple zones and merging is done in a linear Paul trap:

The long term goal is to create large interconnected trapping structures that can store, transport and reorder ions so that any two ions can be brought together in a common zone.
