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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Ions on a needle's tip - Traps with enhanced optical and physical access

Robert Maiwald, Dietrich G. Leibfried, J. Britton, Jonas Bergquist, Gerd Leuchs, David J. Wineland

Published Jun 1, 2009• 0 citations

Abstract

The properties of single atomic ions allow them to be used as sensitive probes to measure a multitude of physical effects, ranging from light field distributions to weak force fields, for example electric or magnetic fields. However trapping and controlling ions reliably calls for a more or less encompassing electrode configuration, that depending on the realization can block a substantial amount of access to the ion. Here we present a novel radio-frequency (rf) ion trap geometry that reduces the solid angle obstructed by trap electrodes to a minimum. Since access and proper ion confinement are inherently opposing goals, we realized three different traps with access ranging from 71% to 96% of 4π to characterize the trade-offs. Fabrication, characterization, as well as promising applications of similar traps in quantum optics and field sensing are discussed.

DOI: 10.1109/cleoe-eqec.2009.5192303

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We investigate geometries for efficient coupling of single ions to fiber-coupled light fields for applications in quantum sensing, quantum metrology, and quantum information processing. Specifically, we discuss the integration of fiber-tip microcavities into radio-frequency ion traps. The distortions of the trapping fields induced by the presence of the optical fibers are simulated for a range of ion trap geometries and the most promising arrangements are identified. Finally, we investigate the use of fiber-tip microcavities with non-spherical mirrors for enhanced ion-light coupling at the center of the trap by appropriate shaping of the cavity modes.

Single-atom quantum sensors offer high spatial resolution and high sensitivity to electric and magnetic fields. Among them, trapped ions offer exceptional performance in sensing electric fields, which has been used in particular to probe these in the proximity of metallic surfaces. However, the flexibility of previous work was limited by the use of radio-frequency trapping fields, which has restricted spatial scanning to linear translations, and calls into question whether observed phenomena are connected to the presence of the radio-frequency fields. Here, using a Penning trap instead, we demonstrate a single ion probe which offers three-dimensional position scanning at distances between

50

μ\mathrm{m}

and

450

μ\mathrm{m}

from a metallic surface and above a

200\times200

μ\mathrm{m}^{2}

area, allowing us to reconstruct static and time-varying electric as well as magnetic fields. We use this to map charge distributions on the metallic surface and noise stemming from it. The methods demonstrated here allow similar probing to be carried out on samples with a variety of materials, surface constitutions and geometries, providing a new tool for surface science.

Twisted radio frequency (rf) ion traps, which have electrode configurations that are twisted variants of conventional linear rf ion traps, have been proposed and successfully demonstrated using charged alumina dust particles. When constructed from thin metal wire electrodes, the twisted traps offer excellent optical accessibility to the trapped ions, making them suitable for applications in quantum information technology. In the experimental demonstration, 14 μm-diameter alumina dust particles were charged via discharge and successfully confined in the twisted trap. A linear chain of trapped particles was observed within the trap.

We present two methods for characterization of motional-mode configurations that are generally applicable to the weak- and strong-binding limit of single or multiple trapped atomic ions. Our methods are essential to realize control of the individual as well as the common motional degrees of freedom. In particular, when implementing scalable radio-frequency trap architectures with decreasing ion-electrode distances, local curvatures of electric potentials need to be measured and adjusted precisely, e.g., to tune phonon tunneling and control effective spin-spin interaction. We demonstrate both methods using single

^{25}\text{Mg}^{+}

ions that are individually confined $40\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ above a surface-electrode trap array and prepared close to the ground state of motion in three dimensions.

We present a novel ion trap design which facilitates the integration of an optical fiber cavity into the trap structure. The optical fibers are confined inside hollow electrodes in such a way that tight shielding and free movement of the fibers are simultaneously achievable. The latter enables in situ optimization of the overlap between the trapped ions and the cavity field. Through numerical simulations, we systematically analyze the effects of the electrode geometry on the trapping characteristics such as trap depths, secular frequencies and the optical access angle. Additionally, we simulate the effects of the presence of the fibers and confirm the robustness of the trapping potential. Based on these simulations and other technical considerations, we devise a practical trap configuration that isviable to achieve strong coupling of a single ion.