Ideal intersections for radio-frequency trap networks

Abstract

We investigate the possible form of ideal intersections for two-dimensional rf trap networks suitable for quantum information processing with trapped ions. We show that the lowest order multipole component of the rf field that can contribute to an ideal intersection is a hexapole term uniquely determined by the tangents of the intersecting paths. The corresponding ponderomotive potential does not provide any confinement perpendicular to the paths if these intersect at right angles, indicating that ideal right-angle X-intersections are impossible to achieve with hexapole fields. Based on this result, we propose an implementation of an ideal oblique-X intersection using a threedimensional electrode structure.PACS numbers: 37.10. Gh, 37.10.Ty,41.20.Cv Intersections between network paths are a key ingredient in two-dimensional (2D) rf trap networks which have been proposed to allow large scale quantum information processing (QIP) with trapped ions [1,2,3]. RF traps confine ions by a combination of rf and quasistatic electric fields [4,5] and in an ideal network the rf field and the associated ponderomotive potential vanish in the trapping zones and on dedicated paths between zones but nowhere else. Such ideal trap networks have been demonstrated in one dimension (1D) with segmented linear rf traps where transport as well as splitting and joining of groups of ions have been demonstrated to be possible with a very high degree of control [6,7,8]. In contrast, no ideal 2D trap networks have been identified, although a number of possible intersection geometries for 2D trap networks have been investigated [9,10,11,12,13,14]. The observed shortcomings fall in two broad categories. For T [9], Y [13,15] and some X [10, 11], intersections, a residual rf field is observed in the paths through the intersection which can possibly lead to motional heating [16], in addition to complicating or hindering controlled ion transport [12]. In contrast, some high-symmetry X geometries offer truly field-free paths but fail to be "fully confining" in the sense that there are unwanted lines of zero field allowing ions to escape the trap network [11].In this paper we show that the unique simplest form of an ideal intersection for 2D trap networks is an oblique X and propose an implementation of this intersection based on a three-dimensional (3D) electrode structure that faithfully implements the ideal intersection.The paper is structured as follows: Sec. I defines the basic problem of designing ideal rf trap intersections. In Sec. II we constructively identify a hexapole term uniquely determined by the intersection angle as the only multipole term of hexapole or lower order which can contribute to a zero-field intersection. In Sec. III we investigate the properties of the identified hexapole intersection and show that fully confining hexapole intersections are * janus.wesenberg@materials.ox.ac.uk only possible at oblique intersection angles. Lastly, in Sec. IV we describe an implementation of the ideal intersection based on a 3D electrode ...

Optimised surface-electrode ion-trap junctions for experiments with cold molecular ions

“…A variety of objective functions has been considered [23,24,28,32], and thus, the question arises which physical quantities are relevant when optimising an electrode structure for a given application. First and foremost, the suppression of pseudopotential barriers that impede ion transport is crucial [26]. Note that the position of pseudopotential minima, where the RF field vanishes, solely depends on the trap geometry, and thus is identical for all ion masses.…”

“…The main challenge to the use of SE junctions arises from the fact that the lowest-order multipole component of the RF field at the centre of a given intersection is a hexapole determined by the tangents of the intersecting channels [26]. In RF traps, the trapping potential is usually calculated within the adiabatic approximation [27] in which a time-independent pseudopotential derived from the RF field governs the confinement of ions [19].…”

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“…As with all known junction traps, it is not possible to stabilize a trapped charge with a vanishing RF field and zero ponderomotive potential everywhere [29]. However, a suitable trade in performance characteristics can be achieved by optimizing the predicted performance using a figure of merit as a function of the electrode geometry.…”