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Chinese Physics B

High-Fidelity Detection of a 171 Yb + Qubit via Leakage-Suppressed Shelving

Xinyu Mai, Liyun Zhang, Longxin Wen, Yao Lu

Published May 22, 2026• 0 citations
Publisher

Abstract

Abstract High-fidelity quantum state detection is essential for quantum information processing, yet in trapped-ion systems it is fundamentally limited by state leakage arising from off-resonant excitation during fluorescence detection. Here, we demonstrate a leakage-suppressed detection scheme for 171 Yb + qubits based on stateselective shelving to a metastable 2 D 3/2 manifold. This approach effectively suppresses population leakage and significantly enhances detection fidelity. We achieve an average detection fidelity of 99.88(2)%, representing a significant improvement over conventional methods. The scheme requires minimal additional experimental resources and is compatible with existing qubit-control configurations, supporting mid-circuit measurement in trapped-ion systems. With state-of-the-art total photon detection efficiency, a detection fidelity of 99.98% is projected, highlighting its potential for scalable quantum information processing.

DOI
10.1088/1674-1056/ae71b2

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Physical Review A•Dec 29, 2010•34 citations
Abstract High-fidelity quantum state detection is essential for quantum information processing, yet in trapped-ion systems it is fundamentally limited by state leakage arising from off-resonant excitation during fluorescence detection. Here, we demonstrate a leakage-suppressed detection scheme for 171 Yb + qubits based on stateselective shelving to a metastable 2 D 3/2 manifold. This approach effectively suppresses population leakage and significantly enhances detection fidelity. We achieve an average detection fidelity of 99.88(2)%, representing a significant improvement over conventional methods. The scheme requires minimal additional experimental resources and is compatible with existing qubit-control configurations, supporting mid-circuit measurement in trapped-ion systems. With state-of-the-art total photon detection efficiency, a detection fidelity of 99.98% is projected, highlighting its potential for scalable quantum information processing.
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+.
We present two novel approaches to state detection of qubits defined with trapped ions. The first uses simple pulse sequences from a mode-locked laser to induce state-dependent excitations in less than 1 ns. The resulting atomic fluorescence occurs in the dark, allowing the placement of non-imaging detectors right next to the atom to improve the qubit state detection efficiency and speed.The second employs the long lived F state in Yb+ which has been used in quantum information science almost exclusively for clocks and optical-frequency qubits. We describe how this resource can be used in conjunction with the ground state S1/2 manifold to aid in the scaling of trapped ion quantum information science. Narrow-band optical pumping into the 2F7/2 from one of the conventional 2S1/2 qubit states is projected to achieve a higher state preparation and measurement (SPAM) fidelity than any other demonstrated technique.
We demonstrate high-fidelity Zeeman qubit state detection in a single trapped 88 Sr + ion. Qubit readout is performed by shelving one of the qubit states to a metastable level using a narrow linewidth diode laser at 674 nm, followed by state-selective fluorescence detection. The average fidelity reached for the readout of the qubit state is 0.9989(1). We then measure the fidelity of state tomography, averaged over all possible single-qubit states, which is 0.9979(2). We also fully characterize the detection process using quantum process tomography. This readout fidelity is compatible with recent estimates of the detection error threshold required for fault-tolerant computation, whereas high-fidelity state tomography opens the way for high-precision quantum process tomography.
Abstract Trapped ions are among the leading platforms for quantum technologies, particularly in the field of quantum computing. Detecting states of trapped ions is essential for ensuring high-fidelity readouts of quantum states.In this work, we develop and benchmark a set of methods for ion quantum state detection using images obtained by a highly sensitive camera.By transforming the images from the camera and applying conventional and quantum machine learning methods, including convolution, support vector machine (classical and quantum), and quantum annealing, we demonstrate a possibility to detect the positions and quantum states of ytterbium ions in a Paul trap. Quantum state detection is performed with an electron shelving technique: depending on the quantum state of the ion its fluorescence under the influence of a 369.5 nm laser beam is either suppressed or not. We estimate fidelities for conventional and quantum detection techniques. In particular, conventional algorithms for detecting 171^{171}171Yb+^{+}+, such as the support vector machine and photon statistics-based method,as well as our quantum annealing-based approach, have achieved perfect fidelity, which is beneficial compared to standard techniques. This result may pave the way for ultrahigh-fidelity detection of trapped ions via conventional and quantum machine learning techniques.
Engineering large-scale quantum computers which simultaneously provide high-fidelity quantum operations, low memory errors, low crosstalk, and reasonable resource usage remains an outstanding challenge across quantum computing platforms. In trapped ions, progress has largely focused on alkaline-earth and ytterbium ions, whose simple electronic structures facilitate control over their internal state. Here we investigate singly-ionized yttrium (89Y+^{89}\mathrm{Y}^+89Y+), a two-valence-electron ion whose ground-state manifold hosts a nuclear-spin qubit and which also features a variety of low-lying metastable manifolds, for applications in quantum information processing. Because experimental data are limited, we perform high-resolution laser-induced fluorescence spectroscopy to measure the hyperfine structure of several low-lying levels, and carry out comprehensive electronic structure calculations to determine lifetimes, transition matrix elements, and hyperfine coefficients for manifolds addressable with visible, near-visible, or infrared wavelengths. Using these results, we analyze schemes for qubit storage, initialization, readout, leakage mitigation, and single- and two-qubit gates. These results position 89Y+^{89}\mathrm{Y}^+89Y+ as a uniquely capable next-generation trapped-ion qubit, combining field-insensitive nuclear-spin or clock-qubit storage with spectrally isolated transitions for operations.
Fluorescence of single, trapped 171Yb^{171}\mathrm{Yb}171Yb+{}^{+}+ ions has been experimentally studied as a function of laser polarization, power, and detuning and as a function of magnetic field strength. The suppression of efficient fluorescence by coherent population trapping and the counteracting effect of the magnetic field are found to agree with theoretical predictions. For comparison, a fluorescence study has also been made of the isotope 174Yb^{174}\mathrm{Yb}174Yb+{}^{+}+ for which coherent population trapping is absent on the main fluorescence and laser cooling transition. Finally, state-sensitive fluorescence detection of the 171Yb^{171}\mathrm{Yb}171Yb+{}^{+}+ hyperfine qubit is studied, including the role of coherent population trapping in the optimization of detection parameters. A qubit detection fidelity of greater than 9797%97 is achieved.