Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2603.21003 · PRX Quantum

Proposal for erasure conversion in integer fluxonium qubits

Jiakai Wang, Raymond A. Mencia, Vladimir E. Manucharyan, Maxim G. Vavilov

quant-phSubmitted Mar 22, 2026• Announced Mar 24, 2026• 0 citations
arXivHTMLPDF

Abstract

We propose an erasure conversion scheme on the $|e\rangle-|f\rangle$ and $|g\rangle-|f\rangle$ qubits in integer fluxonium qubits (IFQs), which are both first-order insensitive to $1/f$ flux noise. The $|e\rangle-|f\rangle$ transition is identical to that of a usual fluxonium qubit and hence is expected to have excellent coherence time, while the $|g\rangle-|f\rangle$ transition is additionally protected from the energy relaxation by the parity symmetry. The dominant error in both qubits arises due to the energy relaxation: from $|e\rangle$ to $|g\rangle$ in the $e\text{--}f$ qubit and from $|f\rangle$ to $|e\rangle$ in the $g\text{--}f$ qubit. Such errors can be treated as erasure events, and their efficient detection improves the performance of quantum error-correcting codes. We consider a protocol for such erasure conversion based on the dispersive readout. Our main finding is that, with proper circuit parameter choice, carefully designed gate sets, and the integration of erasure conversion, IFQs promise high effective coherence times.

Journal reference
PRX Quantum 7, 020339 Published 27 May, 2026
DOI
10.1103/jszm-48h7

Related papers

Hardware-efficient erasure-error detection with an integer fluxonium

Junyoung An, Helin Zhang, Jeffrey M. Gertler +13 more

Erasure-error detection can improve the efficiency of quantum error correction by revealing the times and locations of their error events. In this work, we demonstrate erasure conversions and mid-circuit erasure detections in a single integer fluxonium, in which the states $\mathrm{|g\rangle, |f\rangle}$ encode the logical states and $\mathrm{|e\rangle}$ encodes the erasure state. The integer fluxonium suppresses direct $|\mathrm{f} \rangle \rightarrow |\mathrm{g} \rangle$ transitions and allows the dominant $|\mathrm{f} \rangle \rightarrow |\mathrm{e}\rangle$ transitions to be converted into detectable erasures. Furthermore, we identified a design space that nullifies the resonant-frequency shift between the two logical states, enabling ancilla-free mid-circuit erasure checks using the same resonator employed for final readout. By discarding the detected erasure events, we achieved an 8.4-fold increase in the $|\mathrm{f}\rangle$ state lifetime, a 1.38-fold increase in the Hahn-echo time, and a reduction of single-qubit gate error from 0.061(2)% to 0.030(5)%. Our results establish integer fluxonium as a hardware-efficient platform for erasure-error detection and conversion, while identifying the improvements required to realize an effective erasure qubit with high erasure bias.

quant-pharXiv:2607.27123•Jul 30, 2026•0 citations

Converting qubit relaxation into erasures with a single fluxonium

Chenlu Liu, Yulong Li, Jiahui Wang +9 more

Qubits that experience predominantly erasure errors offer distinct advantages for fault-tolerant operation. Indeed, dual-rail encoded erasure qubits in superconducting cavities and transmons have demonstrated high-fidelity operations by converting physical-qubit relaxation into logical-qubit erasures, but this comes at the cost of increased hardware overhead and circuit complexity. Here, we address these limitations by realizing erasure conversion in a single fluxonium operated at zero flux, where the logical state is encoded in its 0-2 subspace. A single, carefully engineered resonator provides both mid-circuit erasure detection and end-of-line (EOL) logical measurement. Post-selection on non-erasure outcomes results in more than four-fold increase of the logical lifetime, from $193~μ$s to $869~μ$s. Finally, we characterize measurement-induced logical dephasing as a function of measurement power and frequency, and infer that each erasure check contributes a negligible error of $7.2\times 10^{-5}$. These results establish integer-fluxonium as a promising, resource-efficient platform for erasure-based error mitigation, without requiring additional hardware.

quant-pharXiv:2601.11086•Jan 19, 2026•0 citations

Characterization and Comparison of Energy Relaxation in Fluxonium Qubits

Kate Azar, Lamia Ateshian, Mallika T. Randeria +19 more

Fluxonium superconducting qubits have demonstrated long coherence times and high single- and two-qubit gate fidelities, making them a favorable building block for superconducting quantum processors. We investigate the dominant limitations to fluxonium qubit energy relaxation time $T_1$ using a set of eight planar, aluminum-on-silicon qubits. We find that a circuit-based model for capacitive dielectric loss best captures the frequency dependence of $T_1$, which we analyze within both a two-level and a six-level energy relaxation model. We convert the measured $T_1$ into an effective capacitive quality factor $Q_\mathrm{C}^{\mathrm{eff}}$ to compare qubits on equal footing, accounting for independently estimated contributions from $1/f$ flux noise and radiative loss to the control and readout circuitry. We apply this methodology to compare qubits from two fabrication processes: a baseline process and one that applies a fluorine-based wet treatment prior to Josephson junction deposition. We resolve a small improvement of (13.8 $\pm$ 8.4$)\%$ in the process mean $Q_\mathrm{C}^{\mathrm{eff}}$, indicating that the fluorine treatment may have reduced loss from the metal-substrate interface, but did not address the primary source of loss in these fluxonium qubits.

quant-pharXiv:2603.23636•Physical Review Research•Mar 26, 2026•0 citations

The Floquet Fluxonium Molecule: Driving Down Dephasing in Coupled Superconducting Qubits

Matthew Thibodeau, Angela Kou, Bryan K. Clark

High-coherence qubits, which can store and manipulate quantum states for long times with low error rates, are necessary building blocks for quantum computers. Here we propose a driven superconducting erasure qubit, the Floquet fluxonium molecule, which minimizes bit-flip rates through disjoint support of its qubit states and suppresses phase flips by a novel second-order insensitivity to flux-noise dephasing. We estimate the bit-flip, phase-flip, and erasure rates through numerical simulations, with predicted coherence times of approximately 50 ms in the computational subspace and erasure lifetimes of about 500 μ s . We also present a protocol for performing high-fidelity single-qubit rotation gates via additional flux modulation, on timescales of roughly 500 ns, and propose a scheme for erasure detection and logical readout. Our results demonstrate the utility of drives for building new qubits that can outperform their static counterparts. Published by the American Physical Society 2024

arXiv:2401.08762•PRX Quantum•Oct 28, 2024•10 citations

Experimental demonstration of flux-pulse-assisted readout on fluxonium qubits

Taryn V. Stefanski, Figen YILMAZ, Martijn F. S. Zwanenburg +4 more

In the pursuit of large-scale, fault-tolerant quantum computation, various superconducting architectures have been investigated as the potential building blocks for these systems. With the need for fast operations with low error rates, fluxonium qubits have recently gained an increasing amount of attention. The fluxonium qubit offers numerous advantages including a large anharmonicity, long coherence times, protection against flux noise, and resilience against dielectric loss. In an effort to maximize the potential of these devices, we employ flux-pulse-assisted readout to increase the signal to noise ratio and, thus, minimize the readout time required. This readout scheme capitalizes on the high dispersive shift afforded by avoided crossings between the readout resonator and higher order fluxonium transitions. We present experimental results in which we display an advantage of flux-pulse-assisted readout over static readout at the so-called "sweet-spot" on multiple fluxonium qubits.

•Jan 1, 2024•0 citations

Erasure conversion for fault-tolerant quantum computing in alkaline earth Rydberg atom arrays

Yue Wu, Shimon Kolkowitz, Shruti Puri +1 more

Abstract Executing quantum algorithms on error-corrected logical qubits is a critical step for scalable quantum computing, but the requisite numbers of qubits and physical error rates are demanding for current experimental hardware. Recently, the development of error correcting codes tailored to particular physical noise models has helped relax these requirements. In this work, we propose a qubit encoding and gate protocol for 171 Yb neutral atom qubits that converts the dominant physical errors into erasures, that is, errors in known locations. The key idea is to encode qubits in a metastable electronic level, such that gate errors predominantly result in transitions to disjoint subspaces whose populations can be continuously monitored via fluorescence. We estimate that 98% of errors can be converted into erasures. We quantify the benefit of this approach via circuit-level simulations of the surface code, finding a threshold increase from 0.937% to 4.15%. We also observe a larger code distance near the threshold, leading to a faster decrease in the logical error rate for the same number of physical qubits, which is important for near-term implementations. Erasure conversion should benefit any error correcting code, and may also be applied to design new gates and encodings in other qubit platforms.

arXiv:2201.03540•Nature Communications•Aug 9, 2022•197 citations
We propose an erasure conversion scheme on the ∣e⟩−∣f⟩|e\rangle-|f\rangle∣e⟩−∣f⟩ and ∣g⟩−∣f⟩|g\rangle-|f\rangle∣g⟩−∣f⟩ qubits in integer fluxonium qubits (IFQs), which are both first-order insensitive to 1/f1/f1/f flux noise. The ∣e⟩−∣f⟩|e\rangle-|f\rangle∣e⟩−∣f⟩ transition is identical to that of a usual fluxonium qubit and hence is expected to have excellent coherence time, while the ∣g⟩−∣f⟩|g\rangle-|f\rangle∣g⟩−∣f⟩ transition is additionally protected from the energy relaxation by the parity symmetry. The dominant error in both qubits arises due to the energy relaxation: from ∣e⟩|e\rangle∣e⟩ to ∣g⟩|g\rangle∣g⟩ in the e–fe\text{--}fe–f qubit and from ∣f⟩|f\rangle∣f⟩ to ∣e⟩|e\rangle∣e⟩ in the g–fg\text{--}fg–f qubit. Such errors can be treated as erasure events, and their efficient detection improves the performance of quantum error-correcting codes. We consider a protocol for such erasure conversion based on the dispersive readout. Our main finding is that, with proper circuit parameter choice, carefully designed gate sets, and the integration of erasure conversion, IFQs promise high effective coherence times.
Erasure-error detection can improve the efficiency of quantum error correction by revealing the times and locations of their error events. In this work, we demonstrate erasure conversions and mid-circuit erasure detections in a single integer fluxonium, in which the states ∣g⟩,∣f⟩\mathrm{|g\rangle, |f\rangle}∣g⟩,∣f⟩ encode the logical states and ∣e⟩\mathrm{|e\rangle}∣e⟩ encodes the erasure state. The integer fluxonium suppresses direct ∣f⟩→∣g⟩|\mathrm{f} \rangle \rightarrow |\mathrm{g} \rangle∣f⟩→∣g⟩ transitions and allows the dominant ∣f⟩→∣e⟩|\mathrm{f} \rangle \rightarrow |\mathrm{e}\rangle∣f⟩→∣e⟩ transitions to be converted into detectable erasures. Furthermore, we identified a design space that nullifies the resonant-frequency shift between the two logical states, enabling ancilla-free mid-circuit erasure checks using the same resonator employed for final readout. By discarding the detected erasure events, we achieved an 8.4-fold increase in the ∣f⟩|\mathrm{f}\rangle∣f⟩ state lifetime, a 1.38-fold increase in the Hahn-echo time, and a reduction of single-qubit gate error from 0.061(2)% to 0.030(5)%. Our results establish integer fluxonium as a hardware-efficient platform for erasure-error detection and conversion, while identifying the improvements required to realize an effective erasure qubit with high erasure bias.
Qubits that experience predominantly erasure errors offer distinct advantages for fault-tolerant operation. Indeed, dual-rail encoded erasure qubits in superconducting cavities and transmons have demonstrated high-fidelity operations by converting physical-qubit relaxation into logical-qubit erasures, but this comes at the cost of increased hardware overhead and circuit complexity. Here, we address these limitations by realizing erasure conversion in a single fluxonium operated at zero flux, where the logical state is encoded in its 0-2 subspace. A single, carefully engineered resonator provides both mid-circuit erasure detection and end-of-line (EOL) logical measurement. Post-selection on non-erasure outcomes results in more than four-fold increase of the logical lifetime, from 193 μ193~μ193 μs to 869 μ869~μ869 μs. Finally, we characterize measurement-induced logical dephasing as a function of measurement power and frequency, and infer that each erasure check contributes a negligible error of 7.2×10−57.2\times 10^{-5}7.2×10−5. These results establish integer-fluxonium as a promising, resource-efficient platform for erasure-based error mitigation, without requiring additional hardware.
Fluxonium superconducting qubits have demonstrated long coherence times and high single- and two-qubit gate fidelities, making them a favorable building block for superconducting quantum processors. We investigate the dominant limitations to fluxonium qubit energy relaxation time T1T_1T1​ using a set of eight planar, aluminum-on-silicon qubits. We find that a circuit-based model for capacitive dielectric loss best captures the frequency dependence of T1T_1T1​, which we analyze within both a two-level and a six-level energy relaxation model. We convert the measured T1T_1T1​ into an effective capacitive quality factor QCeffQ_\mathrm{C}^{\mathrm{eff}}QCeff​ to compare qubits on equal footing, accounting for independently estimated contributions from 1/f1/f1/f flux noise and radiative loss to the control and readout circuitry. We apply this methodology to compare qubits from two fabrication processes: a baseline process and one that applies a fluorine-based wet treatment prior to Josephson junction deposition. We resolve a small improvement of (13.8 ±\pm± 8.4)%)\%)% in the process mean QCeffQ_\mathrm{C}^{\mathrm{eff}}QCeff​, indicating that the fluorine treatment may have reduced loss from the metal-substrate interface, but did not address the primary source of loss in these fluxonium qubits.
High-coherence qubits, which can store and manipulate quantum states for long times with low error rates, are necessary building blocks for quantum computers. Here we propose a driven superconducting erasure qubit, the Floquet fluxonium molecule, which minimizes bit-flip rates through disjoint support of its qubit states and suppresses phase flips by a novel second-order insensitivity to flux-noise dephasing. We estimate the bit-flip, phase-flip, and erasure rates through numerical simulations, with predicted coherence times of approximately 50 ms in the computational subspace and erasure lifetimes of about 500 μ s . We also present a protocol for performing high-fidelity single-qubit rotation gates via additional flux modulation, on timescales of roughly 500 ns, and propose a scheme for erasure detection and logical readout. Our results demonstrate the utility of drives for building new qubits that can outperform their static counterparts. Published by the American Physical Society 2024
In the pursuit of large-scale, fault-tolerant quantum computation, various superconducting architectures have been investigated as the potential building blocks for these systems. With the need for fast operations with low error rates, fluxonium qubits have recently gained an increasing amount of attention. The fluxonium qubit offers numerous advantages including a large anharmonicity, long coherence times, protection against flux noise, and resilience against dielectric loss. In an effort to maximize the potential of these devices, we employ flux-pulse-assisted readout to increase the signal to noise ratio and, thus, minimize the readout time required. This readout scheme capitalizes on the high dispersive shift afforded by avoided crossings between the readout resonator and higher order fluxonium transitions. We present experimental results in which we display an advantage of flux-pulse-assisted readout over static readout at the so-called "sweet-spot" on multiple fluxonium qubits.
Abstract Executing quantum algorithms on error-corrected logical qubits is a critical step for scalable quantum computing, but the requisite numbers of qubits and physical error rates are demanding for current experimental hardware. Recently, the development of error correcting codes tailored to particular physical noise models has helped relax these requirements. In this work, we propose a qubit encoding and gate protocol for 171 Yb neutral atom qubits that converts the dominant physical errors into erasures, that is, errors in known locations. The key idea is to encode qubits in a metastable electronic level, such that gate errors predominantly result in transitions to disjoint subspaces whose populations can be continuously monitored via fluorescence. We estimate that 98% of errors can be converted into erasures. We quantify the benefit of this approach via circuit-level simulations of the surface code, finding a threshold increase from 0.937% to 4.15%. We also observe a larger code distance near the threshold, leading to a faster decrease in the logical error rate for the same number of physical qubits, which is important for near-term implementations. Erasure conversion should benefit any error correcting code, and may also be applied to design new gates and encodings in other qubit platforms.