Review of Scientific Instruments

Microgram BaCl2 ablation targets for trapped ion experiments

Noah Greenberg, Akbar Jahangiri Jozani, Collin J. C. Epstein, Xinghe Tan, Rajibul Islam, Crystal Senko

Published Apr 1, 2024• 2 citations

Abstract

Trapped ions for quantum information processing have been an area of intense study due to the extraordinarily high fidelity operations that have been reported experimentally. Specifically, barium trapped ions have been shown to have exceptional state-preparation and measurement fidelities. The 133Ba+ (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 (BaCl2) ablation targets for use in trapped ion experiments and compare our procedure to previous methods. We outline two recipes for the 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 and neutral fluorescence collection. Our comparison between fabrication techniques and the demonstration of consistent neutral fluorescence paves a path toward reliable loading of 133Ba+ in surface traps and opens opportunities for scalable quantum computing with this isotope.

DOI: 10.1063/5.0198336

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Review of Scientific Instruments

Microgram BaCl2 ablation targets for trapped ion experiments

Noah Greenberg, Akbar Jahangiri Jozani, Collin J. C. Epstein, Xinghe Tan, Rajibul Islam, Crystal Senko

Published Apr 1, 2024• 2 citations

Publisher

Abstract

DOI: 10.1063/5.0198336

Related papers

Microgram $\mathrm{BaCl}_2$ Ablation Targets for Trapped Ion ExperimentsMicrogram $\mathrm{BaCl}_2$ Ablation Targets for Trapped Ion Experiments

Greenberg, Noah, Akbar Jahangiri Jozani, Collin J. C. Epstein +3 more

Trapped ions for quantum information processing has been an area of intense study due to the extraordinarily high fidelity operations that have been reported experimentally. Specifically, barium trapped ions have been shown to have exceptional state-preparation and measurement (SPAM) fidelities. The $^{133}\mathrm{Ba}^+$ ( $I = 1/2$ ) 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.Trapped ions for quantum information processing has been an area of intense study due to the extraordinarily high fidelity operations that have been reported experimentally. Specifically, barium trapped ions have been shown to have exceptional state-preparation and measurement (SPAM) fidelities. The $^{133}\mathrm{Ba}^+$ ($I = 1/2$) 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.

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Justin Christensen

$^{133}$ Ba $^+$ has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1/2 nucleus, visible wavelength electronic transitions, and long D-state lifetimes ($\\tau\\sim $1~min). Using a microgram source of radioactive material, we trap and laser-cool the synthetic \\textit{A} = 133 radioisotope of barium II ($ \\tau_{1/2} \\approx 10.5 $~yr) in a radio-frequency ion trap. To demonstrate high fidelity qubit operations, a number of unknown state energies were needed. We measure the isotope shift and hyperfine structure of the 6$ ^2 $P$ _{1/2}\\leftrightarrow 5^2 $D$ _{3/2}$ electronic transition needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. For high-fidelity operations with electron shelving, we report measurements of the 6 $^2$ P $_{3/2}$ and $5^2$ D $_{5/2}$ hyperfine splittings, as well as the~6 $^2$ P $_{3/2}~\\leftrightarrow~6^2$ S $_{1/2}$ and ~6 $^2$ P $_{3/2}~\\leftrightarrow~5^2$ D $_{5/2}$ transition frequencies. Using these transitions, we demonstrate high-fidelity \\ba \\ hyperfine qubit manipulation with electron shelving detection to benchmark qubit state preparation and measurement (SPAM). Using single-shot, threshold discrimination, we measure an average SPAM fidelity of $\\mathcal{F} = 0.99971(3)$ , a factor of $\\approx$ 2 improvement over the best reported performance of any qubit.Finally, we report the 6 $^2$ P $_{1/2}\\leftrightarrow 5^2$ D $_{3/2}$ electronic transition isotope shift for the rare \\textit{A} = 130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.$^{133}$Ba$^+$ has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1/2 nucleus, visible wavelength electronic transitions, and long D-state lifetimes ($\\tau\\sim $1~min). Using a microgram source of radioactive material, we trap and laser-cool the synthetic \\textit{A} = 133 radioisotope of barium II ($\\tau_{1/2} \\approx 10.5$~yr) in a radio-frequency ion trap. To demonstrate high fidelity qubit operations, a number of unknown state energies were needed. We measure the isotope shift and hyperfine structure of the 6$^2$P$_{1/2}\\leftrightarrow 5^2$D$_{3/2}$ electronic transition needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. For high-fidelity operations with electron shelving, we report measurements of the 6$^2$P$_{3/2}$ and $5^2$D$_{5/2}$ hyperfine splittings, as well as the~6$^2$P$_{3/2}~\\leftrightarrow~6^2$S$_{1/2}$ and ~6$^2$P$_{3/2}~\\leftrightarrow~5^2$D$_{5/2}$ transition frequencies. Using these transitions, we demonstrate high-fidelity \\ba \\ hyperfine qubit manipulation with electron shelving detection to benchmark qubit state preparation and measurement (SPAM). Using single-shot, threshold discrimination, we measure an average SPAM fidelity of $\\mathcal{F} = 0.99971(3)$, a factor of $\\approx$ 2 improvement over the best reported performance of any qubit.Finally, we report the 6$^2$P$_{1/2}\\leftrightarrow 5^2$D$_{3/2}$ electronic transition isotope shift for the rare \\textit{A} = 130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.

Jan 1, 20203 citations

Efficient isotope-selective pulsed laser ablation loading of 174Yb+ ions in a surface electrode trap

Geert Vrijsen, Yuhi Aikyo, Robert Spivey +2 more

Optics ExpressNov 5, 201924 citations

Spectroscopy of a Synthetic Trapped Ion Qubit

David Hucul, Justin E. Christensen, Eric R. Hudson +1 more

^{133}Ba^{+} has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1/2 nucleus and visible wavelength electronic transitions. Using a microgram source of radioactive material, we trap and laser cool the synthetic A=133 radioisotope of barium II in a radio-frequency ion trap. Using the same, single trapped atom, we measure the isotope shifts and hyperfine structure of the 6^{2}P_{1/2}↔6^{2}S_{1/2} and 6^{2}P_{1/2}↔5^{2}D_{3/2} electronic transitions that are needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. We also report the 6^{2}P_{1/2}↔5^{2}D_{3/2} electronic transition isotope shift for the rare A=130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.^{133}Ba^{+} has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1/2 nucleus and visible wavelength electronic transitions. Using a microgram source of radioactive material, we trap and laser cool the synthetic A=133 radioisotope of barium II in a radio-frequency ion trap. Using the same, single trapped atom, we measure the isotope shifts and hyperfine structure of the 6^{2}P_{1/2}↔6^{2}S_{1/2} and 6^{2}P_{1/2}↔5^{2}D_{3/2} electronic transitions that are needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. We also report the 6^{2}P_{1/2}↔5^{2}D_{3/2} electronic transition isotope shift for the rare A=130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.

arXiv:1705.09736Physical Review LettersSep 6, 201740 citations

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.

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.

High-fidelity operation of a radioactive trapped-ion qubit,

^{133}

^+

^{133}

^+

has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1/2 nucleus, visible wavelength electronic transitions, and long D-state lifetimes ($\\tau\\sim

1~min). Using a microgram source of radioactive material, we trap and laser-cool the synthetic \\textit{A} = 133 radioisotope of barium II (

\\tau_{1/2} \\approx 10.5

~yr) in a radio-frequency ion trap. To demonstrate high fidelity qubit operations, a number of unknown state energies were needed. We measure the isotope shift and hyperfine structure of the 6

P

_{1/2}\\leftrightarrow 5^2

D

_{3/2}$ electronic transition needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. For high-fidelity operations with electron shelving, we report measurements of the 6

^2

_{3/2}

and

5^2

_{5/2}

hyperfine splittings, as well as the~6

^2

_{3/2}~\\leftrightarrow~6^2

_{1/2}

and ~6

^2

_{3/2}~\\leftrightarrow~5^2

_{5/2}

transition frequencies. Using these transitions, we demonstrate high-fidelity \\ba \\ hyperfine qubit manipulation with electron shelving detection to benchmark qubit state preparation and measurement (SPAM). Using single-shot, threshold discrimination, we measure an average SPAM fidelity of

\\mathcal{F} = 0.99971(3)

, a factor of

\\approx

2 improvement over the best reported performance of any qubit.Finally, we report the 6

^2

_{1/2}\\leftrightarrow 5^2

_{3/2}

electronic transition isotope shift for the rare \\textit{A} = 130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.