Hopping of an impurity defect in ion crystals in linear traps

Abstract

Ordered arrays of laser-cooled, trapped ions or "ion crystals" are a novel form of matter with a rich variety of equilibrium structures and dynamics. In this thesis, we investigate the hopping mobility of a 172 Yb + impurity ion within a crystal of 171 Yb + ions, confined in a linear Paul trap. The site-to-site hopping of the impurity ion, distinguished by a lack of fluorescence, is studied as a function of the 171 Yb + laser-cooling parameters and of the anisotropy of the trapping potential. The onset of rapid hopping is found to occur when average thermal energies become comparable to the Coulomb potential energy. Furthermore, the hopping rate is enhanced at trap anisotropies near the critical value for the structural phase transition to a two-dimensional zigzag phase. The impurity ion has the highest hopping mobility near the centre of the crystal, which may be intrinsic to the crystal structure and dynamics near the zigzag transition. Simplified molecular-dynamics simulations reproduce several features of the experimental results.iii To my parents, my aunt and my girlfriend.

Structure, dynamics and bifurcations of discrete solitons in trapped ion crystals

“…For a small number of ions and if the axial confinement is much smaller than the radial, sufficiently cooled ions in a quadrupole trap form a crystalline chain along the trap symmetry axis. For a given number of ions and with lower radial confinement, the linear chain configuration becomes unstable, and the global minimum configuration takes the shape of a zigzag [29][30][31][32][33][34][35][36][37], which extends from the center of the trap, with possibly a part of the ions on the sides still in an axial chain. For parameters close enough to the transition from a linear chain, the zigzag is a planar structure.…”

“…The hopping of the massive kink in the crystal of figure 8(b) occurs on a long timescale, and characterizing the exact dynamics requires further studies. The controlled vibrational excitation of the massive kink exploiting its again altered and gapped spectrum in the PN potential and a fast imaging setup will allow us to study the kink with a mass defect and the related dynamics [35,49]. In addition, the kink with a mass defect occurs also in combination with a second kink in the crystal (figures 9(a) and (b)), which leads us to consider configurations of two kinks [11,12,49] and their interaction.…”

Spontaneous nucleation and dynamics of kink defects in zigzag arrays of trapped ions

“…For continuous phase transitions, the Kibble-Zurek mechanism (KZM) provides an intuitive model of domain and defect formation [1,2] and predicts a power-law scaling for the number of defects formed as a function of transition quench rate [2][3][4]. Several experimental tests of the KZM have been done with different degrees of success [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], all with the goal of examining universal behavior across diverse physical systems.…”

“…The experimental set-up is similar to that previously reported [38,39]. We use a linear Paul trap, operating at a radio frequency (rf) of Ω rf /2π = 12 MHz, and composed of four rods with an ion-to-rod spacing of 0.7 mm and two end-caps separated by 2.5 mm, to form a nominally harmonic confining potential for ions.…”

“…We use a linear Paul trap, operating at a radio frequency (rf) of Ω rf /2π = 12 MHz, and composed of four rods with an ion-to-rod spacing of 0.7 mm and two end-caps separated by 2.5 mm, to form a nominally harmonic confining potential for ions. Photo-ionization is used to load a pure crystal of 42-43 174 Yb ions [39,40], which arrange as a linear string in a trap with an axial secular frequency of ω z /2π = 37.6 kHz and transverse frequencies of ω x /2π = 679 kHz and ω y /2π = 658 kHz [ Fig. 1(a)].…”