**September 07 2012**

**New article:Phys. Rev. A 86, 032104 (2012).**

Quantum quenches of ion Coulomb crystals across structural instabilities

Jens D. Baltrusch, Cecilia Cormick and Giovanna Morigi

Phys. Rev. A 86, 032104 (2012).

Quenches in an ion chain can create coherent superpositions of motional states across the linear-zigzag structural transition. The procedure has been described in Baltrusch et al. [ Phys. Rev. A 84 063821 (2011)] and makes use of spin-dependent forces, so that a coherent superposition of the electronic states of one ion evolves into an entangled state between the chain's internal and external degrees of freedom. The properties of the crystalline state so generated are theoretically studied by means of Ramsey interferometry on one ion of the chain. An analytical expression for the visibility of the interferometric measurement is obtained for a chain of an arbitrary number of ions and as a function of the time elapsed after the quench. Sufficiently close to the linear-zigzag instability the visibility decays very fast, but exhibits revivals at the period of oscillation of the mode that drives the structural instability. These revivals have a periodicity that is independent of the crystal size, and they signal the creation of entanglement by the quantum quench.