Observation of power-law scaling for phase transitions in linear trapped   ion crystals
  We report an experimental confirmation of the power-law relationship between the critical anisotropy parameter and ion number for the linear-to-zigzag phase transition in an ionic crystal. Our experiment uses laser cooled calcium ions confined in a linear radio-frequency trap. Measurements for up to 10 ions are in good agreement with theoretical and numeric predictions. Implications on an upper limit to the size of data registers in ion trap quantum computers are discussed. 
D. G. Enzer, M. M. Schauer, J. J. Gomez, M. S. Gulley, M. H.   Holzscheiter, P. G. Kwiat, S. K. Lamoreaux, C. G. Peterson, V...