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arXiv:1907.13331 · npj Quantum Information

High-fidelity manipulation of a qubit enabled by a manufactured nucleus

Justin E. Christensen, David Hucul, Wesley C. Campbell, Eric R. Hudson

Published Apr 14, 2020• 78 citations
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Abstract

Abstract The recently demonstrated trapping and laser cooling of 133Ba+ has opened the door to the use of this nearly ideal atom for quantum information processing. However, before high-fidelity qubit operations can be performed, a number of unknown state energies are needed. Here, we report measurements of the 2P3/2 and 2D5/2 hyperfine splittings, as well as the 2P3/2 ↔ 2S1/2 and 2P3/2 ↔ 2D5/2 transition frequencies. Using these transitions, we demonstrate high-fidelity 133Ba+ 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 $${\mathcal{F}}=0.99971(3)$$ F = 0.99971 ( 3 ) , a factor of ≈2 improvement over the best reported performance of any qubit.

DOI
10.1038/s41534-020-0265-5

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arXiv:2203.01920•Physical Review Letters•Sep 19, 2022•59 citations
Abstract The recently demonstrated trapping and laser cooling of 133Ba+ has opened the door to the use of this nearly ideal atom for quantum information processing. However, before high-fidelity qubit operations can be performed, a number of unknown state energies are needed. Here, we report measurements of the 2P3/2 and 2D5/2 hyperfine splittings, as well as the 2P3/2 ↔ 2S1/2 and 2P3/2 ↔ 2D5/2 transition frequencies. Using these transitions, we demonstrate high-fidelity 133Ba+ 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 F=0.99971(3){\mathcal{F}}=0.99971(3)F=0.99971(3) F = 0.99971 ( 3 ) , a factor of ≈2 improvement over the best reported performance of any qubit.
High-fidelity operation of a radioactive trapped-ion qubit, 133^{133}133Ba+^++
133^{133}133Ba+^++ 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 ($\\tau\\sim 1 min).Usingamicrogramsourceofradioactivematerial,wetrapandlaser−coolthesynthetictextitA=133radioisotopeofbariumII(1~min). Using a microgram source of radioactive material, we trap and laser-cool the synthetic \\textit{A} = 133 radioisotope of barium II (1 min).Usingamicrogramsourceofradioactivematerial,wetrapandlaser−coolthesynthetictextitA=133radioisotopeofbariumII(\\tau_{1/2} \\approx 10.5 yr)inaradio−frequencyiontrap.Todemonstratehighfidelityqubitoperations,anumberofunknownstateenergieswereneeded.Wemeasuretheisotopeshiftandhyperfinestructureofthe6~yr) in a radio-frequency ion trap. To demonstrate high fidelity qubit operations, a number of unknown state energies were needed. We measure the isotope shift and hyperfine structure of the 6 yr)inaradio−frequencyiontrap.Todemonstratehighfidelityqubitoperations,anumberofunknownstateenergieswereneeded.Wemeasuretheisotopeshiftandhyperfinestructureofthe6^2PPP_{1/2}\\leftrightarrow 5^2DDD_{3/2}$ 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 62^22P3/2_{3/2}3/2​ and 525^252D5/2_{5/2}5/2​ hyperfine splittings, as well as the~62^22P3/2 leftrightarrow 62_{3/2}~\\leftrightarrow~6^23/2​ leftrightarrow 62S1/2_{1/2}1/2​ and ~62^22P3/2 leftrightarrow 52_{3/2}~\\leftrightarrow~5^23/2​ leftrightarrow 52D5/2_{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 mathcalF=0.99971(3)\\mathcal{F} = 0.99971(3)mathcalF=0.99971(3), a factor of approx\\approxapprox 2 improvement over the best reported performance of any qubit.Finally, we report the 62^22P1/2leftrightarrow52_{1/2}\\leftrightarrow 5^21/2​leftrightarrow52D3/2_{3/2}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.
Atomic ions can be isolated from their environment through laser-cooling and trapping, making them useful for quantum information processing, measurement, and sensing. A variety of atomic ion species have been used as qubits. Hyperfine qubits with nuclear spin I = 1/2 have demonstrated the long qubit coherence times with simple, robust laser manipulation. Other qubits (I ≠ 1/2) have easily-prepared, long-lived metastable electronic excited states, and simple discrimination between these states allows high fidelity readout. However, none of the naturally- occurring, atomic ions with nuclear spin I = 1/2 have these excited states that are simultaneously long-lived and easy to prepare. We demonstrate loading, cooling, and qubit manipulation of an artificial, I = 1/2 species of barium with visible wavelength lasers: 133Ba+. We achieved a single shot qubit state preparation and readout fidelity of F = 0.9997, the lowest error rate ever achieved by any qubit on any platform.
Qubits encoded in hyperfine states of trapped ions are ideal for quantum computation given their long lifetimes and low sensitivity to magnetic fields, yet they suffer from off-resonant scattering during detection, often limiting their measurement fidelity. In 171Yb+{}^{171}{\text{Yb}}^{+}171Yb+ this is exacerbated by a low fluorescence yield, which leads to a need for complex and expensive hardware, a problematic bottleneck especially when scaling up the number of qubits. We demonstrate a detection routine based on electron shelving to address this issue in 171Yb+{}^{171}{\text{Yb}}^{+}171Yb+ and achieve a $5.6\ifmmode\times\else\texttimes\fi{}$ reduction in single-ion detection error on an avalanche photodiode to $1.8(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in a 100 $\ensuremath{\mu}\mathrm{s}$ detection period and a $4.3\ifmmode\times\else\texttimes\fi{}$ error reduction on an electron multiplying CCD camera with $7.7(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ error in 400 $\ensuremath{\mu}\mathrm{s}$. We further improve the characterization of a repump transition at 760 nm to enable a more rapid reset of the auxiliary 2F7/2{}^{2}{F}_{7/2}2F7/2​ states populated after shelving. Finally, we examine the detection fidelity limit using the long-lived 2F7/2{}^{2}{F}_{7/2}2F7/2​ state, achieving further $300\ifmmode\times\else\texttimes\fi{}$ and $12\ifmmode\times\else\texttimes\fi{}$ reductions in error to $6(7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ and $6.3(3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ in 1 ms on the respective detectors. While shelving-rate limited in our setup, we suggest various techniques to realize this detection method at speeds compatible with quantum information processing, providing a pathway to ultrahigh-fidelity detection in 171Yb+{}^{171}{\text{Yb}}^{+}171Yb+.
^{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.
We present a method of state preparation and measurement (SPAM) that is amenable to trapped ion hyperfine qubits with nuclear spins higher than I = 1/2. The ground states of these higher nuclear spin isotopes do not afford a simple frequency selective preparation scheme on a strong transition, this limitation is circumvented by stroboscopically driving strong and weak transitions. We demonstrate this method achieving a SPAM infidelity of137Ba+qubit used in this work. State preparation is performed by blending standard, fast optical pumping using E1 transitions and narrow microwave or optical E2 transitions addressing the extra states in the I=3/2 isotope of137Ba+. Measurement is performed with repeated coherent shelving to multiple metastable states.
We present a method for achieving high fidelity state preparation and measurement (SPAM) using trapped ion hyperfine qubits with nuclear spins higher than I=1/2I=1/2I=1/2. The ground states of these higher nuclear spin isotopes do not afford a simple frequency-selective state preparation scheme. We circumvent this limitation by stroboscopically driving strong and weak transitions, blending fast optical pumping using dipole transitions, and narrow microwave or optical quadrupole transitions. We demonstrate this method with the I=3/2I=3/2I=3/2 isotope 137Ba+^{137}{\mathrm{Ba}}^{+}137Ba+ to achieve a SPAM infidelity of $(9.0\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ ($\ensuremath{-}40.5\ifmmode\pm\else\textpm\fi{}0.6\text{ }\text{ }\mathrm{dB}$), facilitating the use of a wider range of ion isotopes with favorable wavelengths and masses for quantum computation.