Vertical Ion Transport in a Surface Paul Trap: Escalator and Elevator Approaches

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 – which, to the best of our knowledge, has not been previously proposed. For comparison, we also analyze two configurations of the known “elevator” method, in which the radio-frequency (RF) null is repositioned dynamically via additional electrode voltages. Both approaches enable nearly a twofold change in the ion confinement height above the chip surface.