arXiv:2110.08456 · Physical Review A

Isotope-selective laser ablation ion-trap loading of Ba+137 using a BaCl2 target

Brendan White, Pei Jiang Low, Yvette de Sereville, Matthew Day, Noah Greenberg, Richard Rademacher, Crystal Senko

Published Mar 9, 2022• 15 citations

Abstract

The $^{133}\mathrm{Ba}^{+}$ ion is a promising candidate as a high-fidelity qubit, and the $^{137}\mathrm{Ba}^{+}$ isotope is promising as a high-fidelity qudit $(d>2)$. Barium metal is very reactive, and $^{133}\mathrm{Ba}^{+}$ is radioactive and can only be sourced in small quantities, so the most commonly used loading method, oven heating, is less suited for barium and is currently not possible for $^{133}\mathrm{Ba}^{+}$. Pulsed laser ablation solves both of these problems by utilizing compound barium sources while also giving some distinct advantages, such as fast loading, less displaced material, and lower heat load near the ion trap. Because of the relatively low abundances of the isotopes of interest, a two-step photoionization technique is used, which gives us the ability to selectively load isotopes. Characterization of the ablation process for our ${\mathrm{BaCl}}_{2}$ targets are presented, including observation of neutral and ion ablation-fluence regimes, preparation and conditioning, lifetimes of ablation spots, and plume velocity distributions. We show that by using laser ablation on ${\mathrm{BaCl}}_{2}$ salt targets with a two-step photoionization method, we can produce and trap barium ions reliably. Furthermore, we demonstrate that with our photoionization method, we can trap $^{137}\mathrm{Ba}^{+}$ with an enhanced selectivity compared to its natural abundance.

DOI: 10.1103/physreva.105.033102

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arXiv:2110.08456 · Physical Review A

Isotope-selective laser ablation ion-trap loading of Ba+137 using a BaCl2 target

Brendan White, Pei Jiang Low, Yvette de Sereville, Matthew Day, Noah Greenberg, Richard Rademacher, Crystal Senko

Published Mar 9, 2022• 15 citations

arXiv HTML PDF

Abstract

The

^{133}\mathrm{Ba}^{+}

ion is a promising candidate as a high-fidelity qubit, and the

^{137}\mathrm{Ba}^{+}

isotope is promising as a high-fidelity qudit

(d>2)

. Barium metal is very reactive, and

^{133}\mathrm{Ba}^{+}

is radioactive and can only be sourced in small quantities, so the most commonly used loading method, oven heating, is less suited for barium and is currently not possible for

^{133}\mathrm{Ba}^{+}

. Pulsed laser ablation solves both of these problems by utilizing compound barium sources while also giving some distinct advantages, such as fast loading, less displaced material, and lower heat load near the ion trap. Because of the relatively low abundances of the isotopes of interest, a two-step photoionization technique is used, which gives us the ability to selectively load isotopes. Characterization of the ablation process for our

{\mathrm{BaCl}}_{2}

targets are presented, including observation of neutral and ion ablation-fluence regimes, preparation and conditioning, lifetimes of ablation spots, and plume velocity distributions. We show that by using laser ablation on

{\mathrm{BaCl}}_{2}

salt targets with a two-step photoionization method, we can produce and trap barium ions reliably. Furthermore, we demonstrate that with our photoionization method, we can trap

^{137}\mathrm{Ba}^{+}

with an enhanced selectivity compared to its natural abundance.

DOI: 10.1103/physreva.105.033102

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The

^{133}\mathrm{Ba}^{+}

ion is a promising candidate as a high-fidelity qubit, and the

^{137}\mathrm{Ba}^{+}

isotope is promising as a high-fidelity qudit

(d>2)

. Barium metal is very reactive, and

^{133}\mathrm{Ba}^{+}

is radioactive and can only be sourced in small quantities, so the most commonly used loading method, oven heating, is less suited for barium and is currently not possible for

^{133}\mathrm{Ba}^{+}

{\mathrm{BaCl}}_{2}

{\mathrm{BaCl}}_{2}

salt targets with a two-step photoionization method, we can produce and trap barium ions reliably. Furthermore, we demonstrate that with our photoionization method, we can trap

^{137}\mathrm{Ba}^{+}

with an enhanced selectivity compared to its natural abundance.

Microgram

\mathrm{BaCl}_2

Ablation Targets for Trapped Ion Experiments

^{133}\mathrm{Ba}^+

(

I = 1/2

) isotope in particular is a promising candidate for large-scale quantum computing experiments. However, a major pitfall with this isotope is that it is radioactive and is thus generally used in microgram quantities to satisfy safety regulations. We describe a new method for creating microgram barium chloride (

\mathrm{BaCl}_2

) ablation targets for use in trapped ion experiments and compare our procedure to previous methods. We outline two recipes for fabrication of ablation targets that increase the production of neutral atoms for isotope-selective loading of barium ions. We show that heat-treatment of the ablation targets greatly increases the consistency at which neutral atoms can be produced and we characterize the uniformity of these targets using trap-independent techniques such as energy dispersive x-ray spectroscopy (EDS) and neutral fluorescence collection. Our comparison between fabrication techniques and demonstration of consistent neutral fluorescence paves a path towards reliable loading of

^{133}\mathrm{Ba}^+

in surface traps and opens opportunities for scalable quantum computing with this isotope.

Trapping

\mathbf{Ba}^+

with Seven-fold Enhanced Efficiency Utilizing an Autoionizing Resonance

^{138}\mathrm{Ba}^+

ions. We show that a two-step photoionization scheme ending in an autoionizing transition increases the ion loading rate nearly an order of magnitude compared to an established technique which does not excite an autoionizing state. The only additional technology required to implement the autoionizing transition is a commercial diode laser. Our technique can be extended to all isotopes of barium, and autoionizing resonances exist in every species currently used for trapped ion quantum processing, making this a promising technique to drastically increase the loading rates for all trapped ion computers.