Yttrium ion as a platform for quantum information processing
Christopher N. Gilbreth, Dmytro Filin, Marianna S. Safronova, Guanming Lao, Eric R. Hudson
Abstract
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 (), 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 as a uniquely capable next-generation trapped-ion qubit, combining field-insensitive nuclear-spin or clock-qubit storage with spectrally isolated transitions for operations.
AI Impact Assessments
(3 models)Scientific Impact Assessment: "Yttrium ion as a platform for quantum information processing"
1. Core Contribution
This paper presents a comprehensive characterization of 89Y+ as a candidate trapped-ion qubit, combining experimental spectroscopy, ab initio electronic structure calculations, and detailed proposals for quantum operations. The central novelty is the identification and rigorous analysis of a two-valence-electron ion with nuclear spin I=1/2 that provides a qualitatively new type of trapped-ion qubit: a nuclear spin qubit in a J=0 ground state (5s² ¹S₀), combined with a rich landscape of metastable manifolds from 4d5s and 4d² configurations. This is fundamentally distinct from all currently deployed trapped-ion qubits (Ba+, Ca+, Sr+, Yb+), which use single-valence-electron ions. The key innovation is the separation of storage (nuclear spin, extremely field-insensitive) from operations (metastable manifolds, spectrally and magnetically distinct), addressing the crosstalk and memory error challenges that limit scaling of current trapped-ion processors.
2. Methodological Rigor
The paper employs a multi-pronged approach with strong internal consistency checks:
Experimental: High-resolution laser-induced fluorescence spectroscopy of cryogenically cooled 89Y+ produced by laser ablation into a buffer gas cell at 20 K. Hyperfine constants for 5s5p ³P₁, 4d5s ³D₁, and 4d5s ³D₂ are measured, with the ³D₁ and ³D₂ values agreeing well with the only prior measurement (Wännström et al. 1994). The ³P₁ measurement appears to be the first.
Theoretical: CI+all-order calculations provide transition matrix elements, lifetimes, and hyperfine coefficients for 25 levels. Error estimation is performed systematically by comparing CI+all-order with CI-MBPT results and including multiple correction terms (core-Brueckner, structural radiation, two-particle, normalization). The agreement between measured and calculated hyperfine coefficients (e.g., A(³P₁) = -532(7) MHz experimental vs. -557(15) MHz theoretical) provides confidence in the calculations where no experimental data exist.
Quantum operations analysis: Shelving, gate, and measurement schemes are analyzed with realistic error models including spontaneous emission (via a carefully derived two-photon master equation), polarization imperfections, and pointing errors. The master equation formalism (Appendix B) extends prior treatments by including counter-rotating terms and multi-level dephasing effects, representing a methodological contribution in its own right.
One limitation is that all operational proposals remain theoretical — no trapping or manipulation of 89Y+ has been demonstrated. The predicted 4d5s ³D₁ lifetime of ~10¹⁰ s, while exciting, is extraordinarily long and essentially unmeasurable directly; its accuracy relies entirely on the theoretical framework.
3. Potential Impact
Trapped-ion quantum computing: If experimentally validated, 89Y+ could address several critical scaling challenges simultaneously. The nuclear spin qubit's magnetic sensitivity of 0.21 kHz/Gauss (vs. 2.5 kHz/Gauss for ¹⁷¹Yb+ at 4 G) directly translates to reduced memory errors. The spectral isolation between storage and operation manifolds could dramatically reduce crosstalk during measurement — a key bottleneck in large-scale systems. The compatibility with magnetic gradient gates while maintaining field-insensitive storage is particularly valuable, as it solves the tension between needing field sensitivity for gates and field insensitivity for memory.
OMG-style architectures: The paper provides a concrete, well-analyzed platform for the omg protocol, which was previously proposed but lacked an ideal atomic species. 89Y+ appears naturally suited to this approach.
Broader atomic physics: The comprehensive electronic structure calculations (Table VI with ~100+ transitions) represent a valuable data resource for the atomic physics community working on Group III ions. The hyperfine quenching analysis of ³P₀ (branching fraction ~2×10⁻⁹) demonstrates techniques applicable to other divalent systems.
4. Timeliness & Relevance
This work is highly timely. Trapped-ion quantum computing is at an inflection point where scaling beyond ~100 qubits requires addressing crosstalk, memory errors, and resource efficiency simultaneously. The paper directly targets these bottlenecks. The parallel development of nuclear spin qubits in neutral atom platforms (¹⁷¹Yb, ⁸⁷Sr optical tweezer arrays) provides both context and motivation — 89Y+ brings similar nuclear spin advantages into the trapped-ion ecosystem with its inherent advantages of long coherence times and individual addressability. The paper's timing also aligns with growing interest in omg-style protocols and multi-qubit-per-atom schemes.
5. Strengths & Limitations
Key Strengths:
Notable Limitations:
Summary
This paper makes a compelling theoretical and partially experimental case for 89Y+ as a next-generation trapped-ion qubit. Its primary value lies in identifying a genuinely new qubit modality in the trapped-ion space and providing the atomic physics characterization needed to pursue it experimentally. The impact will ultimately depend on experimental validation, but the thoroughness of the analysis and the clear advantages identified make this a significant contribution that is likely to stimulate experimental effort.
Generated Apr 20, 2026
Comparison History (44)
Paper 2 introduces a foundational AI approach to a fundamental bottleneck in quantum physics: simulating many-body dynamics. By generalizing across both Hamiltonians and initial states, it provides a scalable computational tool with broad applications across condensed matter physics, quantum chemistry, and quantum computing. In contrast, Paper 1 presents a highly rigorous but more narrowly focused advancement in trapped-ion qubit hardware. The broad applicability, timeliness of AI for science, and potential to surpass exact diagonalization give Paper 2 a higher potential for widespread scientific impact.
The Universal Neural Propagator introduces a fundamentally new paradigm for simulating quantum many-body dynamics by learning operators rather than states, enabling transferability across both Hamiltonians and initial states simultaneously. This represents a significant conceptual advance with broad applicability across quantum physics, materials science, and quantum computing. Paper 2, while valuable for the trapped-ion community, is more incremental—characterizing a specific ion species as a qubit platform. Paper 1's methodology has broader cross-disciplinary impact and addresses a more universal computational challenge.
Paper 2 identifies and characterizes a novel trapped-ion qubit platform (Y+) with comprehensive experimental spectroscopy and theoretical calculations, directly addressing the critical challenge of scalable quantum computing. It proposes concrete schemes for all essential qubit operations and demonstrates unique advantages over existing ion species. This has high practical impact for the quantum computing community. Paper 1, while providing a valuable theoretical unification of quantum jump trajectories and related formalisms, is more incremental in connecting existing mathematical frameworks rather than opening a fundamentally new experimental direction.
Paper 2 demonstrates higher potential scientific impact due to its direct application to quantum computing hardware. While Paper 1 offers a valuable theoretical unification of open quantum system dynamics, Paper 2 introduces and experimentally characterizes a novel platform (the Yttrium ion) for trapped-ion quantum computers. By proposing concrete solutions to critical challenges like memory errors and crosstalk, Paper 2 paves the way for scalable next-generation quantum information processing. Its blend of experimental spectroscopy, theoretical calculation, and immediate real-world technological applicability makes it exceptionally timely and impactful.
Paper 1 develops a physical prototype of a programmable quantum light source, demonstrating immediate, practical solutions for photonic quantum technologies. Its ability to arbitrarily tune both state and temporal waveforms without degradation provides broad, immediate applicability. Paper 2 presents valuable foundational work and spectroscopic analysis for a new trapped-ion qubit candidate, but remains mostly theoretical and analytical in its quantum information applications, making its impact less immediate.
Paper 2 presents a programmable quantum light source that solves a key bottleneck in photonic quantum technologies by decoupling state and waveform tuning while avoiding optical loss. Its demonstrated prototype offers immediate, versatile utility across various quantum optics applications, promising broader and more immediate impact than Paper 1, which primarily explores a novel but early-stage ion candidate requiring significant future engineering to compete with established trapped-ion platforms.
Paper 2 has higher potential impact: it proposes and characterizes a new trapped-ion species (89Y+) for scalable quantum computing, combining spectroscopy with comprehensive electronic-structure calculations to enable concrete gate/readout/storage schemes. This is novel platform-enabling work with broad applicability across ion trapping, atomic physics, and quantum engineering, and is timely given the push for better qubit coherence and reduced crosstalk. Paper 1 is rigorous and relevant but is a more incremental, device-specific diagnostic of TLS-induced readout failure in superconducting qubits, likely narrower in cross-field reach.
Paper 2 has higher potential impact due to greater novelty (introducing and characterizing 89Y+ as a new trapped-ion QIP platform) and broader applicability: it enables new experimental directions, hardware choices, and gate/readout architectures across the trapped-ion community. It combines new high-resolution spectroscopy with comprehensive electronic-structure calculations and explicitly maps results to practical QIP schemes (storage, readout, leakage, gates), increasing real-world relevance and timeliness. Paper 1 is rigorous and important for superconducting-qubit reliability, but is a narrower, defect-specific mechanism with more incremental cross-field reach.
Paper 1 introduces a comprehensive investigation of yttrium ion as a novel trapped-ion qubit platform, combining spectroscopy, electronic structure calculations, and detailed gate scheme analyses. This positions a new physical system for quantum computing with unique advantages (field-insensitive storage, spectrally isolated transitions), potentially opening an entirely new experimental direction in trapped-ion quantum computing. Paper 2 presents a useful algorithmic contribution for quantum sampling, but its impact is more incremental within the existing quantum machine learning landscape. Paper 1's experimental and theoretical foundation for a new qubit platform has broader and more lasting impact on the quantum computing hardware community.
Paper 1 presents comprehensive experimental spectroscopy and theoretical calculations characterizing Y+ as a new trapped-ion qubit platform, providing concrete data (hyperfine structure, lifetimes, matrix elements) and detailed analysis of qubit operations. This fills a significant gap in the trapped-ion quantum computing landscape with immediately actionable results. Paper 2 introduces an interesting theoretical concept of quantum actuators for global control, but remains more abstract and conceptual without experimental validation. Paper 1's combination of experimental measurements, ab initio calculations, and practical gate schemes gives it broader and more immediate impact on the active trapped-ion community.
Paper 1 presents a comprehensive investigation of a new trapped-ion qubit platform (Y+), combining experimental spectroscopy with extensive theoretical calculations to establish its viability for quantum computing. It addresses multiple aspects (storage, gates, readout, leakage mitigation) and identifies unique advantages over existing platforms, potentially opening a new research direction. Paper 2 demonstrates important engineering progress in chip-integrating diamond NV centers at cryogenic temperatures, but represents an incremental step in an established field. Paper 1's broader scope and novelty of proposing an entirely new qubit platform give it higher potential impact.
Paper 1 proposes a new trapped-ion qubit platform (Y+) with comprehensive spectroscopic measurements and theoretical analysis, addressing a core challenge in quantum computing scalability. It opens a new experimental direction with concrete schemes for all essential qubit operations. Paper 2 provides interesting but incremental insights into adversarial robustness of equivariant quantum ML models—a narrower topic with less immediate practical relevance given current quantum hardware limitations. Paper 1's breadth of impact across quantum computing hardware, atomic physics, and engineering gives it significantly higher potential impact.
Paper 1 presents a comprehensive characterization of yttrium ion as a new trapped-ion qubit platform, combining experimental spectroscopy with theoretical calculations and detailed analysis of quantum computing operations. This has broad, immediate practical impact for the quantum computing community by introducing a viable next-generation qubit with unique advantages. Paper 2, while innovative in its quasiparticle preparation method for quantum simulations, addresses a more specialized problem within quantum simulation of scattering. Paper 1's potential to influence experimental quantum computing hardware development gives it broader and more transformative impact.
Paper 2 has higher likely impact: it isolates a key coherence-limiting mechanism in gatemon qubits via a rigorous on-chip controlled comparison (co-fabricated reference transmons), detailed loss budgeting, and temperature-dependent diagnostics that point to junction-intrinsic dissipation. This addresses a timely bottleneck for scalable superconducting qubits and directly guides materials/process improvements with broad relevance to hybrid Josephson devices. Paper 1 is valuable platform-enabling spectroscopy/modeling for a new trapped-ion species, but is more exploratory and may require substantial follow-on engineering to translate into widely adopted hardware.
Paper 2 likely has higher scientific impact due to strong timeliness and broad real-world relevance: identifying and characterizing a new trapped-ion species for scalable quantum computing addresses a central bottleneck in the field. It combines experimental spectroscopy with ab initio electronic-structure calculations and concrete gate/readout/mitigation proposals, enabling near-term adoption by multiple labs. The potential applications span quantum computation, precision metrology, and atomic physics. Paper 1 is conceptually novel in nonequilibrium thermodynamics, but its impact is more specialized and its experimental/technological pathway is less immediate.
Paper 2 introduces and rigorously evaluates a novel trapped-ion platform for quantum computing, addressing major outstanding challenges like high-fidelity operations and large-scale engineering. Its potential to serve as a next-generation qubit gives it a broader and more immediate real-world impact in the rapidly growing field of quantum information processing compared to the more specialized optomechanical PID control explored in Paper 1.
Paper 2 has higher likely impact: it proposes and substantively characterizes a new trapped-ion species (89Y+) for quantum computing, combining new spectroscopy data with extensive electronic-structure calculations and concrete operation schemes (storage, gates, readout). This is timely and broadly relevant to quantum hardware development, potentially enabling improved scalability and coherence across multiple subfields (AMO physics, quantum computing, metrology). Paper 1 is a useful protocol-level refinement in semi-quantum signatures, but its scope is narrower and impact depends on adoption and security proof strength beyond the abstract.
Paper 2 proposes and experimentally characterizes a novel hardware platform for trapped-ion quantum computing. Introducing a new, viable qubit candidate addresses foundational challenges in quantum hardware scalability, fidelity, and operations, likely offering a broader and longer-lasting impact than the algorithmic machine-learning improvement for noisy quantum data presented in Paper 1.
Paper 1 is more novel and potentially disruptive: it proposes an all-photonic, measurement-device-independent QKD protocol that surpasses a fundamental rate–loss benchmark (single-repeater bound) and offers improved scaling (≈η^{2/5}) without ideal quantum memories, with clear relevance to near-term quantum networks. Its impact could span quantum cryptography, network architecture, and photonic implementations. Paper 2 is rigorous and useful for a specific hardware platform, but it is primarily a characterization/enabling study; its broader impact depends on subsequent experimental adoption of 89Y+ as a leading trapped-ion qubit.
Paper 1 introduces a novel physical platform (yttrium ion) for quantum computing, backed by both experimental data and theoretical calculations. Identifying a new, highly capable qubit candidate addresses fundamental hardware scaling challenges, offering potentially massive impact across quantum information science. Paper 2 provides a valuable but more niche theoretical framework for quantum distance-bounding, which has a narrower scope of impact compared to advancing the core hardware underlying all of quantum computing.