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arXiv:2512.10514 · Physical Review Applied

Rapid all-optical loading of trapped ions using a miniaturised atom source

Lorenzo Versini, Tim F. Wohlers-Reichel, Catherine E. J. Challoner, Thomas Hinde, Arjun D. Rao, William J. Hughes, Peter Drmota, Thomas H. Doherty, Laurent J. Stephenson, Jacob A. Blackmore, Joseph F. Goodwin

physics.atom-phquant-phSubmitted Dec 11, 2025• Announced Dec 12, 2025• 0 citations
v1 · Dec 11, 2025v2 · Jun 9, 2026
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Abstract

We characterise an efficient optically-heated neutral atom source for ion trapping. We observe loading rates of up to $24(3)\,\mathrm{s}^{-1}$ with heating powers below $85\,\mathrm{mW}$, and demonstrate loading of a single ion in under $30\,\mathrm{s}$ with $41.4(4)\,\mathrm{mW}$ of optical power in a room-temperature ion trap system with an ionisation probability of $1.50(5)\times10^{-5}$. We calibrate a thermal model for the source's internal temperature by imaging the fluorescence of a collimated flux of neutral calcium that effuses from the oven at various optical heating powers. We show that the thermal performance of this oven is mainly limited by radiative losses. We explore the effect of second-stage photo-ionisation laser power on the loading rate, and identify a path beyond the loading rates reported in this study. We predict that this source is also well-suited to a wide range of metals used in ion-trapping.

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We demonstrate loading of ions into a surface-electrode trap (SET) from a remote, laser-cooled source of neutral atoms. We first cool and load $\ensuremath{\sim}$106{10}^{6}106 neutral 88{}^{88}88Sr atoms into a magneto-optical trap from an oven that has no line of sight with the SET. The cold atoms are then pushed with a resonant laser into the trap region where they are subsequently photoionized and trapped in an SET operated at a cryogenic temperature of 4.6 K. We present studies of the loading process and show that our technique achieves ion loading into a shallow (15 meV depth) trap at rates as high as 125 ions/s while drastically reducing the amount of metal deposition on the trap surface as compared with direct loading from a hot vapor. Furthermore, we note that due to multiple stages of isotopic filtering in our loading process, this technique has the potential for enhanced isotopic selectivity over other loading methods. Rapid loading from a clean, isotopically pure, and precooled source may enable scalable quantum-information processing with trapped ions in large, low-depth surface-trap arrays that are not amenable to loading from a hot atomic beam.
We present a compact cold-wall oven that is simple to build and align for loading miniature ion traps with calcium ions. The cold-wall oven, which is a metal-loaded capillary heated only through a portion of its length by the passage of a current, is described and characterized. An atomic beam with a low divergence of 14 mrad is produced. We perform Doppler-sensitive, resonant fluorescence measurements on the atomic beam to characterize the oven's performance. The emission of atoms from the oven is seen within ∼70 s after turning on the oven at an electric power consumption of <10 W. The flow rate is measured to be 1.5 ± 0.2 × 109 atoms s-1 at a temperature of 702 ± 7 K. The entire oven assembly is mounted on a CF16 feedthrough. This design can be extended to other species for producing a collimated atomic beam.
A range of experimental techniques for application in reaction studies between ionic and neutral atoms/molecules and high resolution spectroscopy experiments with sympathetically cooled molecular ions are presented. A novel ion trap loading scheme using the photo-ionisation of atoms generated by the pulsed laser ablation of a solid calcium target has been characterised. We have identified the range of ablation laser fluences that must be used in order to produce a flux of neutral calcium atoms, which is a prerequisite for isotope selective ion trap loading. Calcium ions are trapped and laser cooled in a linear radio-frequency ion trap. We have developed a spectroscopy scheme that allows the entire fluorescence spectrum of trapped ions to be rapidly collected with high precision while maintaining a low ion temperature and good ion localisation throughout interrogation. The scheme has been demonstrated by measuring the saturation intensity of the calcium ion 4S1/2?4P1/2 transition. We have developed a novel scheme to measure the secular motion of trapped ions and demonstrated the application of the technique to ion-neutral collision reaction experiments. Employing pulsed excitation and Doppler velocimetry, we have measured the centre-of-mass mode frequency of single ions as well as large ion crystals with a frequency precision better than 2x10-3 within an interrogation time on the order of seconds. This method has been used to measure the mass of ions and observe charge exchange collisions between trapped calcium isotopes. In particular, we have measured the 44Ca++40Ca!40Ca++44Ca reaction cross section and demonstrated the single-event resolution of the technique. Finally, we have developed a novel all-optical broadband scheme for exciting, amplifying and measuring the secular motion of ions in the trap. Oscillation induced by optical excitation has been coherently amplified to control and measure the ion's secular motion. Requiring only a single interrogation laser, the ion's oscillation amplitude can be precisely controlled. The application of this technique to non-destructive spectroscopy of trapped molecular ions is discussed.
Trapped-ion technology is a leading approach for scalable quantum computing. A key element of ion trapping is reliable loading of atomic sources into the trap. While thermal atomic ovens have traditionally been used for this purpose, laser ablation has emerged as a viable alternative in recent years, offering the advantages of faster and more localized loading with lower heat dissipation. Calcium is a well-established ion for qubit applications. Here we examine a range of calcium sources for ablation and provide a comprehensive analysis of each. We consider factors such as ease of use, temperature and yield of the ablation plume, and the lifetime of ablation spots. For each target, we estimate the number of trappable atoms per ablation pulse for a typical surface and 3D ion trap.
The authors present an all-optical technique for loading ion traps that has a number of advantages over conventional thermal atom sources. In our experiment a pulsed Nd:YAG laser at 1064 nm, with pulse energies up to 80 muJ and pulse durations in the region of 30 ns, is incident on a calcium metal surface. This generates a pulsed beam of atomic calcium from the metal surface. The atoms are subsequently photo-ionized in a resonant two-photon process by 272 nm light from a frequency-quadrupled fibre laser.