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

Applied Physics Letters

DC flux crosstalk reduction with dual flux line

Zhengqi Niu, Wanpeng Gao, Xiaoliang He, Y. D. Wang, Zhen Wang, Zhirong Lin

Published Jun 17, 2024• 5 citations
Publisher

Abstract

Flux-tunable superconducting qubits offer the potential for quantum information processing and simulation. However, flux crosstalk complicates achieving precise qubit frequency control, as characterizing and compensating for it becomes more challenging when scaling up circuits. In this study, we propose a design featuring a dual flux line for flux-tunable superconducting qubits, consisting of a pair of parallel current lines directing the current back to the enclosure. We conduct experimental comparisons of the DC flux crosstalk between the dual flux line design and the traditional one-way approach within a single chip. We observe a significant reduction in the DC flux crosstalk when utilizing the dual flux line, as supported by electromagnetic field simulations. Our design introduces an approach to scaling up flux-tunable superconducting circuits while maintaining a modest on-chip footprint.

DOI
10.1063/5.0208859

Related papers

Characterizing and mitigating flux crosstalk in superconducting qubits–couplers system

Myrron Albert Callera Aguila, N. Li, Chen-Hsun Ma +12 more

Superconducting qubits have achieved exceptional gate fidelities, exceeding the error-correction threshold in recent years. One key ingredient of such improvement is the introduction of tunable couplers to control the qubit-to-qubit coupling through frequency tuning. Moving toward fault-tolerant quantum computation, increasing the number of physical qubits is another step toward effective error correction codes. Under a multiqubit architecture, flux control (Z) lines are crucial in tuning the frequency of the qubits and couplers. However, dense flux lines result in magnetic flux crosstalk, wherein magnetic flux applied to one element inadvertently affects neighboring qubits or couplers. This crosstalk obscures the idle frequency of the qubit when flux bias is applied, which degrades gate performance and calibration accuracy. In this study, we characterize flux crosstalk and suppress it in a multiqubit-coupler chip with multi-Z lines without adding additional readout for couplers. By quantifying the mutual flux-induced frequency shifts of qubits and couplers, we construct a cancellation matrix that enables precise compensation of non-local flux, demonstrating a substantial reduction in Z-line crosstalk from 56.5‰ to 0.13‰, which is close to statistical error. Flux compensation corrects the CZ SWAP measurement, leading to a symmetric map with respect to flux bias. Compared with a crosstalk-free calculated CZ SWAP map, the measured map indicates that our approach provides a near-zero crosstalk for the coupler-transmon system. These results highlight the effectiveness of our approach in enhancing flux crosstalk-free control and supporting its potential for scaling superconducting quantum processors.

APL Quantum•Feb 18, 2026•2 citations

Superconducting Flux Memory for Cryogenic Applications

Gregory R. Boyd, Jeremy Clark, Mark Covington +15 more

We report the development of flux memory for use with superconducting circuits. This technology stores persistent currents in superconducting loops on-chip to be used to provide flux biasing for superconducting circuits, like qubits. We developed three types of flux memory and draw comparisons among them for circuit design. We demonstrate the utility of flux memory by using an in-situ flux detector and characterize each approach and further demonstrate that once flux is set in a memory cell, benchtop DC control sources can be powered off, leaving the on-chip flux bias in place. We propose that flux memory can be arranged in a two-dimensional configuration to multiplex control signals and reduce how line counts scale (N^2 devices -> 2N control lines), and our experimental results pave the path to the proposed scalability. We demonstrate the use of flux memory to flux bias a transmon qubit and show the tunability of the qubit state to a target frequency which remained stable on-chip for 20 hours.

quant-pharXiv:2609.00772•Sep 2, 2026•0 citations

Calibration of Flux Crosstalk in Large-Scale Flux-Tunable Superconducting Quantum Circuits

Xi Dai, Daniel Tennant, Robbyn Trappen +16 more

Magnetic flux tunability is an essential feature in most approaches to quantum computing based on superconducting qubits.Independent control of the fluxes in multiple loops is hampered by crosstalk.Calibrating flux crosstalk becomes a challenging task when the circuit elements interact strongly.We present a novel approach to flux crosstalk calibration, which is circuit model independent and relies on an iterative process to gradually improve calibration accuracy.This method allows us to reduce errors due to the inductive coupling between loops.The calibration procedure is automated and implemented on devices consisting of tunable flux qubits and couplers with up to 27 control loops.We devise a method to characterize the calibration error, which is used to show that the errors of the measured crosstalk coefficients are all below 0.17%.

arXiv:2105.14360•PRX Quantum•Oct 20, 2021•39 citations

Inherent flux crosstalk and coupler-driven single-qubit gates in superconducting circuits

Balázs Gulácsi, Guido Burkard

Crosstalk refers to unwanted qubit addressing. This is particularly detrimental when scaling up quantum information systems because unintended interactions limit their overall performance. For superconducting qubits, tunable couplings and frequency tunability achieved through externally applied magnetic fluxes enable high-fidelity entangling gates; however, they also introduce crosstalk through unintended flux coupling. In this work, we investigate the impact of time-dependent external magnetic fluxes in quantized circuits on superconducting qubit couplings. We find that non-trivial cross-voltage driving emerges between capacitively linked qubits when the magnetic flux threading the SQUID loop of a qubit varies in time, in a manner analogous to Faraday's law of induction. Crucially, we show that this effect enables fast single qubit control through the coupler element in standard tunable-coupler architectures, potentially eliminating the need for individual microwave $XY$ control lines.

quant-pharXiv:2606.10970•Jun 10, 2026•0 citations

Learning-Based Calibration of Flux Crosstalk in Transmon Qubit Arrays

Cora N. Barrett, Amir H. Karamlou, Sarah E. Muschinske +13 more

Superconducting quantum processors comprising flux-tunable data and coupler qubits are a promising platform for quantum computation. However, magnetic flux crosstalk between the flux-control lines and the constituent qubits impedes precision control of qubit frequencies, presenting a challenge to scaling this platform. In order to implement high-fidelity digital and analog quantum operations, one must characterize the flux crosstalk and compensate for it. In this work, we introduce a learning-based calibration protocol and demonstrate its experimental performance by calibrating an array of 16 flux-tunable transmon qubits. To demonstrate the extensibility of our protocol, we simulate the crosstalk matrix learning procedure for larger arrays of transmon qubits. We observe an empirically linear scaling in calibration time with system size while maintaining a median qubit frequency error below 300 kHz.

arXiv:2303.03347•Physical Review Applied•Aug 28, 2023•21 citations

Inherent flux crosstalk and coupler-driven single-qubit gates in superconducting circuits

Anonymous, Guido Burkard

Crosstalk refers to unwanted qubit addressing. This is particularly detrimental when scaling up quantum information systems because unintended interactions limit their overall performance. For superconducting qubits, tunable couplings and frequency tunability achieved through externally applied magnetic fluxes enable high-fidelity entangling gates; however, they also introduce crosstalk through unintended flux coupling. In this work, we investigate the impact of time-dependent external magnetic fluxes in quantized circuits on superconducting qubit couplings. We find that nontrivial cross-voltage driving emerges between capacitively linked qubits when the magnetic flux threading the superconducting loop of a qubit varies in time, in a manner analogous to Faraday’s law of induction. Crucially, we show that this effect enables fast single-qubit control through the coupler element in standard tunable-coupler architectures, potentially eliminating the need for individual microwave X Y control lines.

Physical Review Applied•Sep 21, 2026•0 citations
Flux-tunable superconducting qubits offer the potential for quantum information processing and simulation. However, flux crosstalk complicates achieving precise qubit frequency control, as characterizing and compensating for it becomes more challenging when scaling up circuits. In this study, we propose a design featuring a dual flux line for flux-tunable superconducting qubits, consisting of a pair of parallel current lines directing the current back to the enclosure. We conduct experimental comparisons of the DC flux crosstalk between the dual flux line design and the traditional one-way approach within a single chip. We observe a significant reduction in the DC flux crosstalk when utilizing the dual flux line, as supported by electromagnetic field simulations. Our design introduces an approach to scaling up flux-tunable superconducting circuits while maintaining a modest on-chip footprint.
Superconducting qubits have achieved exceptional gate fidelities, exceeding the error-correction threshold in recent years. One key ingredient of such improvement is the introduction of tunable couplers to control the qubit-to-qubit coupling through frequency tuning. Moving toward fault-tolerant quantum computation, increasing the number of physical qubits is another step toward effective error correction codes. Under a multiqubit architecture, flux control (Z) lines are crucial in tuning the frequency of the qubits and couplers. However, dense flux lines result in magnetic flux crosstalk, wherein magnetic flux applied to one element inadvertently affects neighboring qubits or couplers. This crosstalk obscures the idle frequency of the qubit when flux bias is applied, which degrades gate performance and calibration accuracy. In this study, we characterize flux crosstalk and suppress it in a multiqubit-coupler chip with multi-Z lines without adding additional readout for couplers. By quantifying the mutual flux-induced frequency shifts of qubits and couplers, we construct a cancellation matrix that enables precise compensation of non-local flux, demonstrating a substantial reduction in Z-line crosstalk from 56.5‰ to 0.13‰, which is close to statistical error. Flux compensation corrects the CZ SWAP measurement, leading to a symmetric map with respect to flux bias. Compared with a crosstalk-free calculated CZ SWAP map, the measured map indicates that our approach provides a near-zero crosstalk for the coupler-transmon system. These results highlight the effectiveness of our approach in enhancing flux crosstalk-free control and supporting its potential for scaling superconducting quantum processors.
We report the development of flux memory for use with superconducting circuits. This technology stores persistent currents in superconducting loops on-chip to be used to provide flux biasing for superconducting circuits, like qubits. We developed three types of flux memory and draw comparisons among them for circuit design. We demonstrate the utility of flux memory by using an in-situ flux detector and characterize each approach and further demonstrate that once flux is set in a memory cell, benchtop DC control sources can be powered off, leaving the on-chip flux bias in place. We propose that flux memory can be arranged in a two-dimensional configuration to multiplex control signals and reduce how line counts scale (N^2 devices -> 2N control lines), and our experimental results pave the path to the proposed scalability. We demonstrate the use of flux memory to flux bias a transmon qubit and show the tunability of the qubit state to a target frequency which remained stable on-chip for 20 hours.
Magnetic flux tunability is an essential feature in most approaches to quantum computing based on superconducting qubits.Independent control of the fluxes in multiple loops is hampered by crosstalk.Calibrating flux crosstalk becomes a challenging task when the circuit elements interact strongly.We present a novel approach to flux crosstalk calibration, which is circuit model independent and relies on an iterative process to gradually improve calibration accuracy.This method allows us to reduce errors due to the inductive coupling between loops.The calibration procedure is automated and implemented on devices consisting of tunable flux qubits and couplers with up to 27 control loops.We devise a method to characterize the calibration error, which is used to show that the errors of the measured crosstalk coefficients are all below 0.17%.
Crosstalk refers to unwanted qubit addressing. This is particularly detrimental when scaling up quantum information systems because unintended interactions limit their overall performance. For superconducting qubits, tunable couplings and frequency tunability achieved through externally applied magnetic fluxes enable high-fidelity entangling gates; however, they also introduce crosstalk through unintended flux coupling. In this work, we investigate the impact of time-dependent external magnetic fluxes in quantized circuits on superconducting qubit couplings. We find that non-trivial cross-voltage driving emerges between capacitively linked qubits when the magnetic flux threading the SQUID loop of a qubit varies in time, in a manner analogous to Faraday's law of induction. Crucially, we show that this effect enables fast single qubit control through the coupler element in standard tunable-coupler architectures, potentially eliminating the need for individual microwave XYXYXY control lines.
Superconducting quantum processors comprising flux-tunable data and coupler qubits are a promising platform for quantum computation. However, magnetic flux crosstalk between the flux-control lines and the constituent qubits impedes precision control of qubit frequencies, presenting a challenge to scaling this platform. In order to implement high-fidelity digital and analog quantum operations, one must characterize the flux crosstalk and compensate for it. In this work, we introduce a learning-based calibration protocol and demonstrate its experimental performance by calibrating an array of 16 flux-tunable transmon qubits. To demonstrate the extensibility of our protocol, we simulate the crosstalk matrix learning procedure for larger arrays of transmon qubits. We observe an empirically linear scaling in calibration time with system size while maintaining a median qubit frequency error below 300 kHz.
Crosstalk refers to unwanted qubit addressing. This is particularly detrimental when scaling up quantum information systems because unintended interactions limit their overall performance. For superconducting qubits, tunable couplings and frequency tunability achieved through externally applied magnetic fluxes enable high-fidelity entangling gates; however, they also introduce crosstalk through unintended flux coupling. In this work, we investigate the impact of time-dependent external magnetic fluxes in quantized circuits on superconducting qubit couplings. We find that nontrivial cross-voltage driving emerges between capacitively linked qubits when the magnetic flux threading the superconducting loop of a qubit varies in time, in a manner analogous to Faraday’s law of induction. Crucially, we show that this effect enables fast single-qubit control through the coupler element in standard tunable-coupler architectures, potentially eliminating the need for individual microwave X Y control lines.