Speaker
Description
Trapped atomic ions are among the most advanced technologies for realizing quantum computation and quantum simulation, based on a combination of high-fidelity quantum gates and long coherence times[1]. Most two-qubit quantum gates for trapped ions are based on collective vibrational modes (phonons), such as the Mølmer–Sørensen gate[2]. While these gates have demonstrated high two-qubit gate fidelities with error rates as low as 10$^{-4}$ as well as reduced sensitivity to ion temperature[3], these systems remain inherently one-dimensional, limiting their scalability. A different entanglement process in trapped-ion systems relies on dipole–dipole Rydberg interactions and has demonstrated sub-microsecond gate times[4], making it one of the fastest gate implementations realized in such systems. The dipole-dipole Rydberg interaction enables two-dimensionnal qubit connectivity beyond linear architectures. To excite ions into Rydberg states, we plan to use a STIRAP sequence with 243 nm and 305 nm lasers[4]. However, these UV lasers can generate stray charges in the vicinity of the trap, producing stray electric fields that increase the motional heating rate and lead to decoherence.
In this work, we will investigate stray electric fields arising from surface charging induced by UV laser exposure on ion trap surfaces. This effect of photo-electrically generated charges is strengthened by the presence of dielectric material near the trap electrode, such as the silicon dioxide substrate located in the inter-electrode gaps where charge accumulation may occur. The static component of the stray electric field is measured using phase-resolved fluorescence measurements[5], by correlating photon arrival times with the RF trapping drive phase. Oscillating stray fields lead to ion heating and will be characterized using a thermometry technique based on dark resonances[6]. This method has the advantage of addressing all vibrational modes simultaneously, without the need for multiplexing. We implement this method to characterize the motional heating rate of our surface Paul trap and investigate its evolution upon UV laser exposure in the vicinity of the trap.
[1]: HARTY, T. P., et al. High-fidelity preparation, gates, memory, and readout of a trapped-ion quantum bit. Physical Review Letters, 2014
[2]: MOLMER, K., SORENSEN, A. Multiparticle entanglement in a hot ion trap. Physical Review Letters, 1999, 82, 1835–1838.
[3]: HUGHES, A. C., et al. Trapped-ion two-qubit gates with $>$99.99\% fidelity without ground-state cooling. arXiv preprint arXiv:2510.17286, 2025. \url{https://arxiv.org/abs/2510.17286}
[4]: ZHANG, Chi, et al. Submicrosecond entangling gate between trapped ions via Rydberg interaction. Nature, 2020.
[5]: BERKELAND, D. J., MILLER, J. D., BERQUIST, J. C., ITANO, W. M., WINELAND, D. J. Minimization of ion micromotion in a Paul trap. Journal of Applied Physics, 1998, 83, 5025.
[6]: TUGAYÉ, V., LIKFORMAN, J.-P., GUIBAL, S., GUIDONI, L. Absolute single-ion thermometry. Physical Review A, 2019, 99, 023412.
| Academic level | PhD student |
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