**May 05 2013**

**07.-09.05.2013 visit of Tanja Mehlstäubler**

Tanja Mehlstäubler ( PTB Braunschweig) visits us and gives a talk about "Symmetry Breaking and Topological Defect Formation in Ion Coulomb Crystals" in the Ctrl-Q seminar on Wednesday 08.05.2013, 09.00 in E.04.

Abstract:

K. Pyka1, J. Keller1, H.L. Partner1, R. Nigmatullin2,3, T.

Burgermeister1, D.M. Meier1, K. Kuhlmann1, A. Retzker4, M.B.

Plenio2,3,5, W.H. Zurek6, A. del Campo6,7 & T.E. Mehlstäubler1

Structural defects in ion Coulomb crystals (kinks) have been proposed

for studies of quantum-mechanical effects with solitons and as

carriers of quantum information [1]. Defects form when a symmetry

breaking phase transition is crossed and the finite speed of

information prevents different regions from coordinating the choice of

the symmetry broken state. Where such local choices are incompatible,

defects will form with densities predicted to follow a power law

scaling in the rate of the transition. The importance of this

Kibble-Zurek mechanism (KZM) ranges from cosmology to condensed matter

[2-4]. In previous tests in homogeneous systems, defect formation was

seen, but weak dependence on the transition rate and limited control

of external parameters so far prevented tests of KZM scaling. As

recently predicted [5], in inhomogeneous systems propagation of the

critical front enhances the role of causality and steepens scaling of

defect density with the transition rate. We use ion Coulomb crystals

in a harmonic trap to demonstrate, for the first time, scaling of the

number of topological defects with the transition rate ? the central

prediction of KZM - in a well-controlled environment [6]. We will

detail on kink dynamics and stability in our system.

[1] Landa et al., Phys. Rev. Lett. 104, 043004 (2010)

[2] Kibble, T. W. B. Some implications of a cosmological phase

transition. Phys. Rep. 67, 183-199 (1980).

[3] Zurek, W. H. Cosmological experiments in superfluid helium? Nature

317, 505 (1985).

[4] Monaco, R., Mygind, J., Rivers, R. J., Koshelets, V. P.

Spontaneous fluxoid formation in superconducting

loops. Phys. Rev. B 80, 180501(R) (2009).

[5] del Campo, A., De Chiara, G., Morigi, G., Plenio, M. B., Retzker,

A. Structural Defects in Ion Chains by

Quenching the External Potential: The Inhomogeneous

Kibble-Zurek Mechanism. Phys. Rev. Lett. 105,

075701 (2010).

[6] Pyka et al., arXiv:1211.7005 (2012)