arXiv:1004.1161 · Physical Review A

Hyperfine and optical barium ion qubits

Matthew Dietrich, Nathan Kurz, T. Noel, Gang Shu, B. B. Blinov

Published May 20, 2010• 41 citations

Abstract

State preparation, qubit rotation, and high fidelity readout are demonstrated for two different $^{137}\mathrm{Ba}{}^{+}$ qubit types. First, an optical qubit on the narrow $6{S}_{1/2}$ to $5{D}_{5/2}$ transition at 1.76 $\ensuremath{\mu}$m is implemented. Then, leveraging the techniques developed there for readout, a ground-state hyperfine qubit using the magnetically insensitive transition at 8 GHz is accomplished.

DOI: 10.1103/physreva.81.052328

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arXiv:1004.1161 · Physical Review A

Hyperfine and optical barium ion qubits

Matthew Dietrich, Nathan Kurz, T. Noel, Gang Shu, B. B. Blinov

Published May 20, 2010• 41 citations

arXiv HTML PDF

Abstract

State preparation, qubit rotation, and high fidelity readout are demonstrated for two different

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

qubit types. First, an optical qubit on the narrow

6{S}_{1/2}

5{D}_{5/2}

transition at 1.76

\ensuremath{\mu}

m is implemented. Then, leveraging the techniques developed there for readout, a ground-state hyperfine qubit using the magnetically insensitive transition at 8 GHz is accomplished.

DOI: 10.1103/physreva.81.052328

Related papers

High Fidelity State Preparation and Measurement of Ion Hyperfine Qubits with I>12

Fangzhao Alex An, Anthony Ransford, Andrew Schaffer +4 more

We present a method for achieving high fidelity state preparation and measurement (SPAM) using trapped ion hyperfine qubits with nuclear spins higher than $I=1/2$ . 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 $I=3/2$ isotope $^{137}{\mathrm{Ba}}^{+}$ 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.We present a method for achieving high fidelity state preparation and measurement (SPAM) using trapped ion hyperfine qubits with nuclear spins higher than $I=1/2$. 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 $I=3/2$ isotope $^{137}{\mathrm{Ba}}^{+}$ 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.

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133Ba+: High fidelity goldilocks qubits (Conference Presentation)

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A. D. Leu, Matthew C. Smith, Mario F. Gely +1 more

Quantum state preparation for trapped-ion qubits often relies on high-quality circularly polarized light, which may be difficult to achieve with chip-based integrated optics technology. We propose and implement a hybrid optical and microwave scheme for intermediate-field hyperfine qubits which instead relies on frequency selectivity. Experimentally, we achieve 99.94 % fidelity for linearly polarized ( σ + / σ − ) light, using Ca + 43 at 28.8 mT. We find that the fidelity remains above 99.8 % for a mixture of all polarizations ( σ + / σ − / π ) . We calculate that the method is capable of 99.99 % fidelity in Ca + 43 , and even higher fidelities in heavier ions such as Ba + 137 . Published by the American Physical Society 2024Quantum state preparation for trapped-ion qubits often relies on high-quality circularly polarized light, which may be difficult to achieve with chip-based integrated optics technology. We propose and implement a hybrid optical and microwave scheme for intermediate-field hyperfine qubits which instead relies on frequency selectivity. Experimentally, we achieve 99.94 % fidelity for linearly polarized ( σ + / σ − ) light, using Ca + 43 at 28.8 mT. We find that the fidelity remains above 99.8 % for a mixture of all polarizations ( σ + / σ − / π ) . We calculate that the method is capable of 99.99 % fidelity in Ca + 43 , and even higher fidelities in heavier ions such as Ba + 137 . Published by the American Physical Society 2024

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State preparation, qubit rotation, and high fidelity readout are demonstrated for two different

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

qubit types. First, an optical qubit on the narrow

6{S}_{1/2}

5{D}_{5/2}

transition at 1.76

\ensuremath{\mu}

m is implemented. Then, leveraging the techniques developed there for readout, a ground-state hyperfine qubit using the magnetically insensitive transition at 8 GHz is accomplished.

We present a method for achieving high fidelity state preparation and measurement (SPAM) using trapped ion hyperfine qubits with nuclear spins higher than

I=1/2

. 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=3/2

isotope

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

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.

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.

^{171}\mathrm{Yb}^{+}

, with a measured coherence time of

2.5\phantom{\rule{0.3em}{0ex}}\mathrm{s}

. The high efficiency and high fidelity of these operations is accomplished through the stabilization and frequency modulation of relevant laser sources.

We propose and demonstrate a protocol for high-fidelity indirect readout of trapped ion hyperfine qubits, where the state of a

^{9}{\mathrm{Be}}^{+}

qubit ion is mapped to a

^{25}{\mathrm{Mg}}^{+}

readout ion using laser-driven Raman transitions. By partitioning the

^{9}{\mathrm{Be}}^{+}

ground-state hyperfine manifold into two subspaces representing the two qubit states and choosing appropriate laser parameters, the protocol can be made robust to spontaneous photon scattering errors on the Raman transitions, enabling repetition for increased readout fidelity. We demonstrate combined readout and back-action errors for the two subspaces of ${1.2}_{\ensuremath{-}0.6}^{+1.1}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and ${0}_{\ensuremath{-}0}^{+1.9}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ with 68% confidence while avoiding decoherence of spectator qubits due to stray resonant light that is inherent to direct fluorescence detection.