Optically induced structural phase transitions in ion Coulomb crystals

Abstract

We investigate numerically the structural dynamics of ion Coulomb crystals confined in a threedimensional harmonic trap when influenced by an additional one-dimensional optically induced periodical potential. We demonstrate that transitions between thermally excited crystal structures, such as body-centered cubic and face-centered cubic, can be suppressed by a proper choice of the potential depth and periodicity. Furthermore, by varying the harmonic trap parameters and/or the optical potential in time, controlled transitions between crystal structures can be obtained with close to unit efficiency.PACS numbers: 37.10. Ty, 37.10.Vz, 64.70.kp, 36.40.Ei When an ensemble of confined ions with the same sign of charge is cooled to a sufficiently low temperature, the ionic system forms a crystalline structure [1], often referred to as an ion Coulomb crystal. Since the first experimental realizations of ion Coulomb crystals through laser cooling of atomic ions into the milli-Kelvin regime in electromagnetic traps [2,3], there has been growing theoretical [4][5][6][7][8][9][10][11][12][13][14] and experimental [15][16][17][18][19][20][21][22][23][24] interest in studying the structural and dynamic properties of these crystals under different trapping conditions and for various ion compositions.The unique localization and isolation of the individual ions constituting the crystals have already led to a large number of amazing results within precision measurements [25], cavity quantum electrodynamics (CQED) [26][27][28][29][30], quantum information science [31][32][33][34][35], and cold molecular science [36][37][38][39]. For experiments involving larger three-dimensional ion Coulomb crystals, such as CQED related experiments [26,27] with the interesting prospect of creating quantum memories and other quantum devices, full structural control of the crystal structures is still in need for optimizing the coupling between the ions and the cavity modes.While the energetic ground state of very large threedimensional Coulomb crystals ( > ∼ 10 5 ions) in a harmonic confinement is known to be a body-centered cubic (bcc) lattice [1], the energetically most favorable configuration for smaller crystals ( < ∼ 10 3 ions) is ions situated in concentric shells [5]. For medium sized crystals often employed in experiments [26, 27] (∼ 10 3 − 10 5 ions), the structure is generally not very stable, and thermally induced transitions between a large variety of states including metastable bcc and fcc structures and incommensurable crystallite formations can be observed [40,41]. While structural stability can be dramatically increased using two-species crystals [21,23], means to control and manipulate the structures of single-species crystals are highly wanted, not only for applications in quantum information science, but also for exploiting Coulomb crys- In this Letter, we report on molecular dynamics (MD) simulations of harmonically trapped ion Coulomb crystals in the presence of an additional periodically corrugated potential in the form of a...

Exploring structural phase transitions of ion crystals

“…The laser-cooled ions confined in radio-frequency (rf) traps and Penning traps can condense into crystalline states and form different ordered configurations under control of the confining potentials 1 2 3 4 5 6 7 8 9 10 11 12 . The variation of the configurations corresponds to structural phase transitions of the ion crystals, such as the linear-to-zigzag phase transition predicted in theory 13 14 and later experimentally verified 15 16 17 .…”

Operator-based derivation of phonon modes and characterization of correlations for trapped ions at zero and finite temperature

“…Progress in recent decades in quantum optics and trapped ion systems have provided a versatile platform to investigate a broad range of physical phenomena. At sufficiently low temperatures, and depending on the interactions, geometry and parameters of the trap, the contained ions form a variety of crystalline structures [1][2][3][4][5][6][7][8][9][10][11]. Particular focus has been cast upon the transition between the linear and the zigzag configurations for a long 1D ion chain, both experimentally [1][2][3][4] and theoretically [12][13][14][15][16][17][18][19][20][21].…”

Sub-micron positioning of trapped ions with respect to the absolute center of a standing-wave cavity field

“…First, it adds to the tools for trapping ions in localized optical fields [15,16] for coherent atom-ion studies [36][37][38][39]. Second, superposing a steep and short-scale periodic optical potential to a shallow rf trap allows studies of structural [20][21][22] and dynamical phase transitions (e.g. Coulomb-Frenkel-Kontorova model [23][24][25][26]40]).…”

“…The interest here has been partly to demonstrate * drewsen@phys.au.dk trapping of a single ion with localized fields in order to e.g. enable coherent interactions between atoms and ions without perturbation induced by trapping fields [19], partly to superpose a steep periodic potential to a shallow rf trap potential with the aim of studying structural [20][21][22] and dynamical phase transitions (e.g. CoulombFrenkel-Kontorova model [23][24][25][26]), as well as enhancing the coupling strength between ions and cavity photons with quantum memory [27,28] and photon counter [29] applications in mind.…”