arXiv:2309.11809 · Scientific Reports

Preparing pure $$^{43}$$Ca$$^+$$ samples in an ion trap with photoionization and parametric excitations

C-H Kuo, Y. -C. Hsiao, C. -Y. Jhang, Y.-D. Chen, Shih-Kuang Tung

Published Aug 9, 2024• 3 citations

Abstract

Abstract We present a practical scheme for the efficient preparation of laser-cooled 43Ca+ ions in an ion trap. Our approach integrates two well-established methods: isotope-selective photoionization and isotope-specific parametric excitation. Drawing inspiration from the individual merits of each method, we have successfully integrated these techniques to prepare extended chains of 43Ca+ ions, overcoming the challenge posed by their low natural abundance of 0.135% in a natural source. Furthermore, we explore the subtleties of our scheme, focusing on the influence of different factors on the purification process. Our investigation contributes to a broader understanding of the technique and highlights the adaptability of established methods in addressing specific isotopic challenges.

DOI: 10.1038/s41598-024-69166-0

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arXiv:2309.11809 · Scientific Reports

Preparing pure $^{43}$ Ca $^+$ samples in an ion trap with photoionization and parametric excitationsPreparing pure $$^{43}$$Ca$$^+$$ samples in an ion trap with photoionization and parametric excitations

C-H Kuo, Y. -C. Hsiao, C. -Y. Jhang, Y.-D. Chen, Shih-Kuang Tung

Published Aug 9, 2024• 3 citations

arXiv HTML PDF

Abstract

DOI: 10.1038/s41598-024-69166-0

Related papers

Selective Loading of Rare Calcium Isotope 43Ca+ using Photo-Ionization

Isamu Morita, U. Tanaka, Shinji Urabe

Rare calcium isotope 43Ca+ ion (0.135%) is the only naturally abundant isotope with hyperfine structure. This isotope is considered an attractive candidate both for an optical frequency standard and for quantum information processing. We report a method to load 43Ca+ ions selectively into a linear Paul trap using a two-step, resonant photo-ionization process. Isotope selectivity is achieved by utilizing the isotope shifts for the resonant 4s2 1S0-4s4p 1P1 transition of neutral calcium. The second non-resonant excitation is achieved by an ultraviolet light emitting diode (LED). The use of an LED is simpler and more economical than using a laser for the second transition. Additionally the laser cooling of 43Ca+ is demonstrated using two ultraviolet-diode lasers and two infrared-diode lasers. Due to the hyperfine structure, the laser requirements for Doppler cooling 43Ca+ are more demanding than for the other isotopes.Rare calcium isotope 43Ca+ ion (0.135%) is the only naturally abundant isotope with hyperfine structure. This isotope is considered an attractive candidate both for an optical frequency standard and for quantum information processing. We report a method to load 43Ca+ ions selectively into a linear Paul trap using a two-step, resonant photo-ionization process. Isotope selectivity is achieved by utilizing the isotope shifts for the resonant 4s2 1S0-4s4p 1P1 transition of neutral calcium. The second non-resonant excitation is achieved by an ultraviolet light emitting diode (LED). The use of an LED is simpler and more economical than using a laser for the second transition. Additionally the laser cooling of 43Ca+ is demonstrated using two ultraviolet-diode lasers and two infrared-diode lasers. Due to the hyperfine structure, the laser requirements for Doppler cooling 43Ca+ are more demanding than for the other isotopes.

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Isotope-selective photoionization for calcium ion trapping

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We present studies of resonance-enhanced photoionization for isotope-selective loading of ${\mathrm{Ca}}^{+}$ into a Paul trap. The ${4s}^{2}{}^{1}{S}_{0}\ensuremath{\leftrightarrow}4s4p{}^{1}{P}_{1}$ transition of neutral calcium is driven by a 423 nm laser and the atoms are photoionized by a second laser at 389 nm. Isotope selectivity is achieved by using crossed atomic and laser beams to reduce the Doppler width significantly below the isotope shifts in the 423 nm transition. The loading rate of ions into the trap is studied under a range of experimental parameters for the abundant isotope ${}^{40}{\mathrm{Ca}}^{+}.$ Using the fluorescence of the atomic beam at 423 nm as a measure of the Ca number density, we estimate a lower limit for the absolute photoionization cross section of 170(60) Mb. We achieve loading and laser cooling of all the naturally occurring isotopes, without the need for enriched sources. Laser heating/cooling is observed to enhance the isotope selectivity. In the case of the rare species ${}^{43}{\mathrm{Ca}}^{+}$ and ${}^{46}{\mathrm{Ca}}^{+},$ which have not previously been laser cooled, the loading is not fully isotope selective, but we show that pure crystals of ${}^{43}{\mathrm{Ca}}^{+}$ may nevertheless be obtained. We find that for loading ${}^{40}{\mathrm{Ca}}^{+}$ the 389 nm laser may be replaced by an incoherent source.We present studies of resonance-enhanced photoionization for isotope-selective loading of ${\mathrm{Ca}}^{+}$ into a Paul trap. The ${4s}^{2}{}^{1}{S}_{0}\ensuremath{\leftrightarrow}4s4p{}^{1}{P}_{1}$ transition of neutral calcium is driven by a 423 nm laser and the atoms are photoionized by a second laser at 389 nm. Isotope selectivity is achieved by using crossed atomic and laser beams to reduce the Doppler width significantly below the isotope shifts in the 423 nm transition. The loading rate of ions into the trap is studied under a range of experimental parameters for the abundant isotope ${}^{40}{\mathrm{Ca}}^{+}.$ Using the fluorescence of the atomic beam at 423 nm as a measure of the Ca number density, we estimate a lower limit for the absolute photoionization cross section of 170(60) Mb. We achieve loading and laser cooling of all the naturally occurring isotopes, without the need for enriched sources. Laser heating/cooling is observed to enhance the isotope selectivity. In the case of the rare species ${}^{43}{\mathrm{Ca}}^{+}$ and ${}^{46}{\mathrm{Ca}}^{+},$ which have not previously been laser cooled, the loading is not fully isotope selective, but we show that pure crystals of ${}^{43}{\mathrm{Ca}}^{+}$ may nevertheless be obtained. We find that for loading ${}^{40}{\mathrm{Ca}}^{+}$ the 389 nm laser may be replaced by an incoherent source.

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Isotope-selective manipulation of Ca+using laser heating and cooling in a linear Paul trap

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We report on the isotope-selective manipulation of Ca + using the laser-heating and laser-cooling techniques in a linear Paul trap. Only 40 Ca + was selectively laser-heated using the optical isotope shift and eliminated from the trap while keeping the target isotope in the trap. The elimination process of the dominant isotope 40 Ca + was investigated and 42, 43, 44, 48 Ca + in the natural isotope mixture of Ca + generated by laser ablation were successfully observed by means of applying the appropriate dc voltage on the end-cap electrodes without changing the laser frequencies, the laser powers and the duration of the laser irradiation. This simplified method enables us to efficiently laser-cool the rare isotopes.We report on the isotope-selective manipulation of Ca + using the laser-heating and laser-cooling techniques in a linear Paul trap. Only 40 Ca + was selectively laser-heated using the optical isotope shift and eliminated from the trap while keeping the target isotope in the trap. The elimination process of the dominant isotope 40 Ca + was investigated and 42, 43, 44, 48 Ca + in the natural isotope mixture of Ca + generated by laser ablation were successfully observed by means of applying the appropriate dc voltage on the end-cap electrodes without changing the laser frequencies, the laser powers and the duration of the laser irradiation. This simplified method enables us to efficiently laser-cool the rare isotopes.

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Collisional and radiative effects in the state-selective preparation of translationally cold molecular ions in ion traps

Xin Tong, Dieter Wild, Stefan Willitsch

We give a detailed characterization of a recently developed method to prepare translationally cold, internally state-selected molecular ions in ion traps [X. Tong, A. H. Winney, and S. Willitsch, Phys. Rev. Lett. 105, 143001 (2010)]. The technique relies on the generation of molecular ions in a well-defined rotational-vibrational quantum state using threshold photoionization followed by sympathetic cooling of the translational motion with laser-cooled Ca ${}^{+}$ ions. We discuss the experimental requirements for the successful generation and sympathetic cooling of state-selected ions, explore the influence of collisional and radiative processes on the population redistribution dynamics, and give an assessment of the scopeof the method.We give a detailed characterization of a recently developed method to prepare translationally cold, internally state-selected molecular ions in ion traps [X. Tong, A. H. Winney, and S. Willitsch, Phys. Rev. Lett. 105, 143001 (2010)]. The technique relies on the generation of molecular ions in a well-defined rotational-vibrational quantum state using threshold photoionization followed by sympathetic cooling of the translational motion with laser-cooled Ca${}^{+}$ ions. We discuss the experimental requirements for the successful generation and sympathetic cooling of state-selected ions, explore the influence of collisional and radiative processes on the population redistribution dynamics, and give an assessment of the scopeof the method.

Physical Review AFeb 18, 201140 citations

Preparing pure

^{43}

^+

samples in an ion trap with photoionization and parametric excitations

We present studies of resonance-enhanced photoionization for isotope-selective loading of

{\mathrm{Ca}}^{+}

into a Paul trap. The ${4s}^{2}{}^{1}{S}_{0}\ensuremath{\leftrightarrow}4s4p{}^{1}{P}_{1}$ transition of neutral calcium is driven by a 423 nm laser and the atoms are photoionized by a second laser at 389 nm. Isotope selectivity is achieved by using crossed atomic and laser beams to reduce the Doppler width significantly below the isotope shifts in the 423 nm transition. The loading rate of ions into the trap is studied under a range of experimental parameters for the abundant isotope

{}^{40}{\mathrm{Ca}}^{+}.

Using the fluorescence of the atomic beam at 423 nm as a measure of the Ca number density, we estimate a lower limit for the absolute photoionization cross section of 170(60) Mb. We achieve loading and laser cooling of all the naturally occurring isotopes, without the need for enriched sources. Laser heating/cooling is observed to enhance the isotope selectivity. In the case of the rare species

{}^{43}{\mathrm{Ca}}^{+}

and

{}^{46}{\mathrm{Ca}}^{+},

which have not previously been laser cooled, the loading is not fully isotope selective, but we show that pure crystals of

{}^{43}{\mathrm{Ca}}^{+}

may nevertheless be obtained. We find that for loading

{}^{40}{\mathrm{Ca}}^{+}

the 389 nm laser may be replaced by an incoherent source.

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.

{}^{+}

ions. We discuss the experimental requirements for the successful generation and sympathetic cooling of state-selected ions, explore the influence of collisional and radiative processes on the population redistribution dynamics, and give an assessment of the scopeof the method.