Coulomb crystals form when the Coulomb interaction between charged particles dominates over kinetic energy; the prototype is the Wigner crystal formed by conduction electrons in metals at low densities. In recent years, it has become possible to realize Coulomb crystals using laser-cooled trapped ions, and these systems allow for unprecedented control of experimental parameters. This review describes the state of the art of ion Coulomb crystals in one, two, and three dimensions, their properties in and out of equilibrium, and their importance across fields ranging from condensed matter to astrophysics.
Ion Coulomb crystals: An exotic form of condensed matter
Giovanna Morigi, John Bollinger, Michael Drewsen, Daniel Podolsky, and Efrat Shimshoni
Rev. Mod. Phys. 98, 035001 (2026)
Keisuke Inomata, Kazunori Kohri, and Takahiro Terada
Rev. Mod. Phys. 98, 045001 (2026) - Published 7 October, 2026
Gravitational waves offer a potential window into the first moments of cosmic history. If the Universe underwent and abruptly exited an early matter-dominated phase, as predicted by many particle-physics models involving heavy particles, primordial black holes, or oscillating scalar fields forming -balls, the resulting gravitational-wave signal could be amplified via the recently discovered “poltergeist mechanism” discussed in this review. The authors explain the physical origin of this amplification, analyze the mechanism across several cosmological scenarios, and discuss prospects for detecting the resulting signals with current and future gravitational-wave observatories.
