Clouds of Trapped Cooled Ions Condense into Crystals

Photographs of ions trapped by electric and magnetic fields are revealing ordered structures ranging from a few ions in crystalline arrays to thousands of ions arranged on the surfaces of concentric shells. In some experiments with a handful of singly charged ions, varying certain parameters of the trap causes the regular structures to dissolve rapidly into clouds and just as rapidly to recrystallize—behavior resembling a phase change or an order‐to‐chaos transition. All these regular structures occur in systems with well‐defined constituents and interactions. As such they can provide useful insights into collective phenomena such as cluster formation, Wigner crystallization and other strongly coupled plasmas.