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arXiv:2604.21350 · Journal of Physics Communications

Vertical Shuttling Protocols for Trapped Ions in Multi-Rail, Multi-Zone Surface Ion Trap Architectures

Qirat Iqbal, Altaf H. Nizamani

quant-phSubmitted Apr 23, 2026• Announced Apr 24, 2026• 0 citations
v1 · Apr 23, 2026v2 · May 10, 2026
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Abstract

We investigate optimized vertical ion-shuttling protocols for trapped-ion applications across a range of ion-trap experiments, including three-dimensional gradient-measurement sensors, on-chip ion fluorescence collection and imaging, improved laser accessibility, and quantum information processing. In this work, we focus on minimizing motional energy gain during ion transport. Our findings indicate that anomalous heating becomes the dominant limiting factor only for shuttling durations exceeding $500~μ\mathrm{s}$, whereas the final motional excitation is strongly dependent on the selected transport protocol. Using a recently measured heating rate of $(3.1 \pm 0.35)$ quanta/ms at an ion--surface separation of $134 \pm 1.5~μ\mathrm{m}$, we demonstrate that the motional excitation can be restricted to fewer than eight quanta when the ion is vertically displaced by $86~μ\mathrm{m}$ from its initial position. These results enable adiabatic shuttling within $0.5~\mathrm{ms}$, thereby meeting the operational requirements for high-fidelity quantum sensing and coherent control.

Journal reference
Journal of Physics Communication, 2026
DOI
10.1088/2399-6528/ae82b3

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We investigate optimized vertical ion-shuttling protocols for trapped-ion applications across a range of ion-trap experiments, including three-dimensional gradient-measurement sensors, on-chip ion fluorescence collection and imaging, improved laser accessibility, and quantum information processing. In this work, we focus on minimizing motional energy gain during ion transport. Our findings indicate that anomalous heating becomes the dominant limiting factor only for shuttling durations exceeding 500 μs500~μ\mathrm{s}500 μs, whereas the final motional excitation is strongly dependent on the selected transport protocol. Using a recently measured heating rate of (3.1±0.35)(3.1 \pm 0.35)(3.1±0.35) quanta/ms at an ion--surface separation of 134±1.5 μm134 \pm 1.5~μ\mathrm{m}134±1.5 μm, we demonstrate that the motional excitation can be restricted to fewer than eight quanta when the ion is vertically displaced by 86 μm86~μ\mathrm{m}86 μm from its initial position. These results enable adiabatic shuttling within 0.5 ms0.5~\mathrm{ms}0.5 ms, thereby meeting the operational requirements for high-fidelity quantum sensing and coherent control.
Abstract Shuttling ions at high speed and with low motional excitation is essential for realizing fast and high-fidelity algorithms in many trapped-ion-based quantum computing architectures. Achieving such performance is challenging due to the sensitivity of an ion to electric fields and the unknown and imperfect environmental and control variables that create them. Here we implement a closed-loop optimization of the voltage waveforms that control the trajectory and axial frequency of an ion during transport in order to minimize the final motional excitation. The resulting waveforms realize fast round-trip transport of a trapped ion across multiple electrodes at speeds of 0.5 electrodes per microsecond (35 m·s −1 for a one-way transport of 210 μm in 6 μs) with a maximum of 0.36 ± 0.08 mean quanta gain. This sub-quanta gain is independent of the phase of the secular motion at the distal location, obviating the need for an electric field impulse or time delay to eliminate the coherent motion.
Surface ion traps are a cornerstone technology for scalable quantum information processing, yet their shallow trap depths and limited ion lifetimes remain fundamental engineering bottlenecks. This study presents a systematic experimental and statistical comparison between standard single-wafer surface traps and a novel multi-wafer surface trap architecture in which two parallel wafers with integrated radio-frequency (RF) electrodes are separated by a controllable vertical gap. Seventeen trap configurations were characterized (N = 5 standard, N = 12 multi-wafer), with wafer separations ranging from 50 to 500 µm. Welch’s independent-samples t-tests revealed that the multi-wafer geometry produced a mean trap depth of 23.53 meV compared with 8.50 meV in standard traps (d = 2.71, p < .001), extended ion lifetimes from 120 s to 620.75 s (d = 2.72, p < .001), and reduced anomalous heating rates from 857 to 153 quanta/s (d = −14.75, p < .001). Pearson correlations showed an exceptionally strong positive relationship between wafer separation and trap depth (r = .999, p < .001), and between trap depth and ion lifetime (r = .997, p < .001). A linear regression model explained 99.4% of the variance in ion lifetime from trap depth alone (R² = .995). Qubit coherence time (T₂*) scaled with trap depth, reaching 18.2 ms in the deepest configuration. Results demonstrate that multi-wafer architectures overcome the characteristic depth saturation (∼5.5 meV) of standard designs and produce deeper, more stable, and longer-lived ion traps suitable for scalable quantum computing. Keywords: surface ion trap, multi-wafer architecture, trap depth, ion lifetime, quantum computing, anomalous heating, vertical confinement
We measure ion heating following transport throughout a Y\mathsf{Y}Y-junction surface-electrode ion trap. By carefully selecting the trap voltage update rate during adiabatic transport along a trap arm, we observe minimal heating relative to the anomalous heating background. Transport through the junction results in an induced heating between 37 and 150 quanta in the axial direction per traverse. To reliably measure heating in this range, we compare the experimental sideband envelope, including up to fourth-order sidebands, to a theoretical model. The sideband envelope method allows us to cover the intermediate heating range inaccessible to the first-order sideband and Doppler recooling methods. We conclude that quantum information processing in this ion trap will likely require sympathetic cooling in order to support high fidelity gates after junction transport.
The development of scalable quantum technologies requires ion-trap architectures that provide strong and stable confinement while minimizing motional heating caused by electric-field noise. Trapped-ion systems offer long coherence times and high-fidelity quantum control; however, anomalous motional heating from electrode surfaces can limit their performance. This study presents a finite-element analysis of a novel inclined ion-trap architecture, focusing on the effects of electrode geometry and blade separation on confinement strength, secular frequencies, motional heating, thermal response, and RF stability. Five trap inclinations were investigated using three-dimensional electrostatic simulations for blade separations of 5 to 35 um. The RF electric-field distribution was used to determine the effective pseudopotential, trap depth, secular frequencies, and normal modes. An empirical electric-field-noise model was then used to estimate the motional heating rate for frequency-noise exponents alpha = 3, 3.5, and 4. The results reveal a trade-off between confinement strength and ion-electrode distance. Blade separations of approximately 25 to 35 um provide a favorable design regime. At 25 um, the predicted heating rate is approximately 127 to 135 quanta per second for alpha = 3, but the RF stability margin is lower (qmax approximately 1.9). At 35 um, the stability is substantially improved (qmax approximately 0.52), while the heating rate increases to approximately 1570 to 1820 quanta per second. These results provide design guidelines for optimizing inclined ion traps for future trapped-ion quantum-information architectures.
We realize fast transport of ions in a segmented microstructured Paul trap. The ion is shuttled over a distance of more than 10(4) times its ground state wave function size during only five motional cycles of the trap (280 μm in 3.6 μs). Starting from a ground-state-cooled ion, we find an optimized transport such that the energy increase is as low as 0.10±0.01 motional quanta. In addition, we demonstrate that quantum information stored in a spin-motion entangled state is preserved throughout the transport. Shuttling operations are concatenated, as a proof-of-principle for the shuttling-based architecture to scalable ion trap quantum computing.
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.