title: Quantum zigzag transition in ion chains.
abstract: A string of trapped ions at zero temperature exhibits a structural phase transition to a zigzag structure, tuned by reducing the transverse trap potential or the interparticle distance. The transition is driven by transverse, short wavelength vibrational modes. We argue that this is a quantum phase transition, which can be experimentally realized and probed. Indeed, by means of a mapping to the Ising model in a transverse field, we estimate the quantum critical point in terms of the system parameters, and find a finite, measurable deviation from the critical point predicted by the classical theory. A measurement procedure is suggested which can probe the effects of quantum fluctuations at criticality. These results can be extended to describe the transverse instability of ultracold polar molecules in a one-dimensional optical lattice.
authors.affiliation: Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel.
authors.forename: Efrat
authors.initials: E
authors.lastname: Shimshoni
authors.forename: Giovanna
authors.initials: G
authors.lastname: Morigi
authors.forename: Shmuel
authors.initials: S
authors.lastname: Fishman