Vertical ion transport in a surface Paul trap: escalator and elevator approaches

Abstract

Surface ion traps confining and manipulating tens of ion qubits have become the leading platform for quantum processors with high quantum volume. These devices employ the Quantum Charge-Coupled Device (QCCD) architecture, wherein multiple trapping zones are linked by an on-chip transport network that shuttles ion chains, enabling full connectivity through physical ion transport in a plane parallel to the chip surface. The ability to move ions perpendicular to this plane can offer additional advantages, including tuning the laser-ion interaction strength, systematic studies of surface-induced heating mechanisms, and precise alignment with a mode of an external optical cavity. We introduce an "escalator" - a geometrically optimized transition between trapping zones of different confinement heights - and present a comparative analysis of two "elevator" configurations that reposition the RF null dynamically via additional electrode voltages. Both approaches enable nearly a twofold change in the ion confinement height above the chip surface.

Figures (9)

• Figure 1: Surface ion trap configurations for vertical ion positioning. (a) Escalator: a transition region connects two trapping zones with a twofold height difference; the blue line shows the ion trajectory during transport. (b) Elevator with a controllable RF voltage $\alpha V_\text{rf}$ applied to the central electrode. (c) Elevator with a controllable RF voltage $\alpha V_\text{rf}$ applied to segments of the central electrode. Two ion positions corresponding to different control voltages are shown in (b) and (c).
• Figure 2: Pseudopotential distribution along the transport axis. (a) Unoptimized connection between two trapping zones of different heights. (b) Optimized transition after all optimization procedures, with a tenfold reduction in the pseudopotential barrier.
• Figure 3: Variable points of an RF electrode along the transition region. During optimization, the x-coordinate of each point is varied while keeping z fixed. The points of the lower RF electrode are constructed symmetrically. The DC electrode is adjusted to maintain a constant gap between adjacent electrodes.
• Figure 4: Optimized electrode geometry of the escalator transition region.
• Figure 5: (a) Pseudopotential barrier along the ion transport path for optimized (red) and non-optimized (blue) transition regions; (b) Height of the pseudopotential minimum versus axial position; (c) Magnitude of the pseudopotential's first derivative.