Isotope-selective laser ablation ion-trap loading of $^{137}\mathrm{Ba}^{+}$ using a ${\mathrm{BaCl}}_{2}$ target

Isotope-selective laser ablation ion-trap loading of ${}^{137}{Ba}^{+}$ using a ${BaCl}_{2}$ target

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

Phys. Rev. A 105, 033102 – Published 9 March 2022; Erratum Phys. Rev. A 108, 039901 (2023)

Abstract

The ${}^{133}{Ba}^{+}$ ion is a promising candidate as a high-fidelity qubit, and the ${}^{137}{Ba}^{+}$ isotope is promising as a high-fidelity qudit $(d > 2)$ . Barium metal is very reactive, and ${}^{133}{Ba}^{+}$ 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 ${}^{133}{Ba}^{+}$ . 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 ${BaCl}_{2}$ 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 ${BaCl}_{2}$ 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 ${}^{137}{Ba}^{+}$ with an enhanced selectivity compared to its natural abundance.

Received 18 October 2021
Accepted 11 February 2022

DOI:https://doi.org/10.1103/PhysRevA.105.033102

Physics Subject Headings (PhySH)

Atom or molecule scattering from surfaces Cooling & trapping Fine & hyperfine structure

Atomic & molecular beams Trapped ions

Atom & ion cooling Optical spectroscopy Photoionization

Atomic, Molecular & OpticalQuantum Information, Science & Technology

Erratum

Erratum: Isotope-selective laser ablation ion-trap loading of ${}^{137}{Ba}^{+}$ using a ${BaCl}_{2}$ target [Phys. Rev. A 105, 033102 (2022)]

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

Phys. Rev. A 108, 039901 (2023)

Authors & Affiliations

Brendan M. White , Pei Jiang Low, Yvette de Sereville, Matthew L. Day , Noah Greenberg, Richard Rademacher, and Crystal Senko^*

Department of Physics and Astronomy, University of Waterloo, Waterloo, N2L 3R1 Canada
and Institute for Quantum Computing, University of Waterloo, Waterloo, N2L 3R1 Canada

^*csenko@uwaterloo.ca

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Vol. 105, Iss. 3 — March 2022

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Figure 1
(a) and (b) Experimental setup for laser ablation trapping. Ablation targets point directly towards the trap center. The ablation laser enters through the top view port. To use the low-volume target, the ionization beams' directions are swapped. (c) and (d) High- and low-density targets, respectively. (e) Relevant energy structure of neutral barium: A two-step photoionization process with 554- and 405-nm lasers [21, 50, 61, 62, 63, 64, 65] is used to eject a valence electron from neutral barium, ionizing it. (f) Relevant energy structure of ionized barium: a 493-nm laser drives the $S_{1 / 2} \leftrightarrow P_{1 / 2}$ transition to Doppler cool the ion and a 650-nm repump laser drives the $D_{3 / 2} \leftrightarrow P_{1 / 2}$ transition. These cooling lasers are co-propogating with the first-step photoionization (554-nm) laser. (g) A chain of four trapped ${}^{138}{Ba}^{+} ions$ with $\sim 13 μ m$ distance between them.
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Figure 2
Neutral-atom and ion production regimes. Diagonally hatched areas denote conditioning fluences. (a) Neutral-atom fluorescence vs pulse fluence. (b) Ion fluorescence and vacuum chamber pressure spikes vs pulse fluence.
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Figure 3
Ablation spot lifetimes and conditioning. First-step photoionization laser power is $\sim 150 \times P_{sat}$ . The inset circles represent the target with the specific spots corresponding to the data labeled. (a) Low-fluence at $0.20 J / c m^{2}$ (top) and conditioning at $0.48 J / c m^{2}$ (bottom). At low-fluence, some spots were high yield, giving over 50 counts. Most spots gave a moderate yield with over 10 counts measured. The remaining spots were low yield, giving counts very near background. (b) Neutral fluorescence spot lifetime for several spots.
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Figure 4
Time-resolved spectroscopy. First-step photoionization laser power $12 \times P_{sat}$ , ablation fluence $0.25 J / c m^{2}$ . (a) Neutral fluorescence collected from our natural-abundance target for different first-step photoionization frequencies and time-window starts. Two spots on the target were used for the data sets with the second spot used for $f \geq 3315 MHz$ . Doppler shifts for a range of angles 0– ${1.7}^{\circ}$ are shown (relevant transitions ${}^{138}{Ba}$ and ${}^{137}{Ba}$ are purple and others in pink) with the fit curves as solid lines. The dotted-purple line denotes the boundary for slow atoms used to generate (b). (b) First-step photoionization spectrum from integrating over the times for slow atoms in (a) [50, 61, 62]. Subscripts on isotopes denote different transitions; (a)–(c) denote $J^{'} = 1 / 2, 3 / 2, 5 / 2$ , respectively (see Table 1). (c) Overall time-of-flight distribution from integrating over all frequencies in (a). (d) Velocity distribution generated by scaling the time-of-flight data in (c) appropriately and converting to velocity (see the text). The dotted line indicates the highest velocity an atom can be trapped with, based on our estimation of trap depth (see the Supplemental Material [69]).
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Figure 5
Selectivity of ${}^{137}{Ba}^{+}$ . Theoretical loading probabilities for isotopes of barium using two-step photoionization $p_{sel}^{th}$ are calculated by comparing their Gaussian curves to the total line shape. Experimentally measured $p_{sel}^{\exp}$ are shown as points. $s_{1}$ and $s_{2}$ denote $5 \times$ and $10 \times$ saturations, respectively.
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Physical Review A

covering atomic, molecular, and optical physics and quantum information

Isotope-selective laser ablation ion-trap loading of ${}^{137}{Ba}^{+}$ using a ${BaCl}_{2}$ target

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

Phys. Rev. A 105, 033102 – Published 9 March 2022; Erratum Phys. Rev. A 108, 039901 (2023)

Abstract

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Erratum

Erratum: Isotope-selective laser ablation ion-trap loading of ${}^{137}{Ba}^{+}$ using a ${BaCl}_{2}$ target [Phys. Rev. A 105, 033102 (2022)]

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

Phys. Rev. A 108, 039901 (2023)

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Physical Review A

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

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

Phys. Rev. A 105, 033102 – Published 9 March 2022; Erratum Phys. Rev. A 108, 039901 (2023)

Abstract

Physics Subject Headings (PhySH)

Erratum

Erratum: Isotope-selective laser ablation ion-trap loading of Ba+137 using a BaCl2 target [Phys. Rev. A 105, 033102 (2022)]

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

Phys. Rev. A 108, 039901 (2023)

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Isotope-selective laser ablation ion-trap loading of ${}^{137}{Ba}^{+}$ using a ${BaCl}_{2}$ target

Erratum: Isotope-selective laser ablation ion-trap loading of ${}^{137}{Ba}^{+}$ using a ${BaCl}_{2}$ target [Phys. Rev. A 105, 033102 (2022)]