Quantum Computer Errors Tracked in Real-Time, Paving Way for Stable Machines
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Scientists are increasingly focused on understanding quasiparticle tunneling events, a significant source of decoherence and errors in superconducting circuits. Simon Sundelin, Linus Andersson, and Hampus Brunander, all from the Department of Microtechnology and Nanoscience at Chalmers University of Technology, alongside Simone Gasparinetti et al., have now demonstrated real-time detection of these events in a multi-qubit superconducting device. Their research represents a substantial step forward because it allows for the characterisation of quasiparticle behaviour at the single-hertz level with microsecond resolution, revealing both uncorrelated individual events and correlated burst episodes. By employing time-tagged coincidence analysis, the team identified bursts occurring approximately once per minute, inducing a thousand-fold increase in tunneling rates and providing crucial insight into the spatial structure of these errors, ultimately paving the way for improved error suppression in future quantum processors. This work focuses on simultaneously detecting these tunneling events in two charge-sensitive transmons coupled to a common waveguide, achieving measurement of background tunneling rates at the single-hertz level with temporal resolution of tens of microseconds. Through time-tagged coincidence analysis, researchers demonstrate that individual quasiparticle tunneling events are uncorrelated between the two devices, while burst episodes, occurring approximately once per minute, exhibit strong correlation. These bursts induce a thousand-fold increase in the quasiparticle tunneling rate across both devices and persist for an average lifetime of 7 milliseconds. The study identifies a rarer subset of these bursts, appearing at a rate of approximately one event per hour, accompanied by a discernible shift in the offset charge. This charge shift suggests the involvement of ionizing events, providing insight into the origins of these disruptive bursts. By continuously monitoring coherent microwave scattering from both transmon qubits, the research team directly observes parity switching induced by quasiparticle tunneling in real time. The ability to detect and characterise these correlated bursts represents a practical and extensible method for identifying quasiparticle dynamics within superconducting circuits. This advancement is crucial for suppressing correlated errors in increasingly complex superconducting quantum processors. Understanding the spatial structure and correlations of these events is paramount, as quantum error-correction codes rely on the assumption of uncorrelated errors. The research establishes a pathway towards mitigating the detrimental effects of quasiparticle tunneling, particularly the bursts that degrade relaxation times in multiple qubits simultaneously. Furthermore, the findings contribute to the ongoing effort to improve qubit coherence through material science advancements and refined shielding techniques.
Microwave Transmission Characterisation of Superconducting Qubit Dynamics reveals coherent control limitations A 72-qubit superconducting processor forms the foundation of this study, enabling simultaneous detection of quasiparticle tunneling events in two co-housed, charge-sensitive transmon qubits. These qubits are directly coupled to a common coplanar waveguide, facilitating real-time monitoring of tunneling activity. Coherent microwave scattering was employed to reveal the charge-parity states of each transmon, with transmitted fields measured to define a transmission coefficient quantifying the scattering response. The experimental setup involved a false-colored optical micrograph revealing the physical arrangement of the qubits and waveguide, with each transmon approximately 14μm in size and separated by 1.5mm. Transmission coefficients were calculated for each detector in both even and odd charge-parity states, allowing identification of corresponding transition frequencies denoted as ω±1 and ω±2. Master-equation simulations, combined with input, output theory, were used to fit the theoretical transmission response to the experimentally obtained data, validating the measurement methodology. Time-tagged coincidence analysis was then implemented to correlate events detected across the two devices. This technique allowed researchers to discern uncorrelated individual events occurring at a rate of approximately one per minute, alongside largely correlated burst episodes. These bursts exhibited a characteristic lifetime of 7ms and induced a thousand-fold increase in the quasiparticle tunneling rate across both qubits. Furthermore, a rarer subset of bursts, occurring at approximately one per hour, were identified as being accompanied by a shift in the offset charge, indicating a change in the charge landscape around the qubits. This methodology provides a practical and extensible method for identifying quasiparticle bursts and their spatial structure, advancing the development of more robust superconducting quantum processors. Correlated quasiparticle bursts and individual tunneling event characteristics reveal underlying dynamics Background quasiparticle tunneling rates were measured at the single-hertz level, with a temporal resolution of tens of microseconds. Simultaneous detection of quasiparticle tunneling events was achieved in two co-housed, charge-sensitive transmons coupled to a common waveguide. Time-tagged coincidence analysis revealed that individual tunneling events across the devices are uncorrelated, establishing a baseline for independent error sources. Burst episodes, occurring approximately once per minute, demonstrated strong correlation between the two devices. These correlated bursts exhibit a characteristic lifetime of 7 milliseconds and induce a thousand-fold increase in the quasiparticle tunneling rate across both devices. The research identified a rarer subset of bursts, observed at a rate of approximately one event per hour, accompanied by a discernible shift in the offset charge. This work establishes a practical and extensible method for identifying quasiparticle bursts in superconducting circuits and characterizing their correlations. The observed bursts’ spatial structure provides insight into the origins of correlated errors. Measurements of the transmission coefficient for the two detectors in even and odd charge-parity states were performed, with corresponding transition frequencies indicated by dashed lines in accompanying figures. Solid lines represent theoretical transmission responses obtained from master-equation simulations combined with input, output theory.
Correlated Quasiparticle Bursts Drive Decoherence in Superconducting Devices, limiting their performance Scientists have developed a method for real-time detection of quasiparticle tunneling events in superconducting circuits, offering a significant advancement in understanding decoherence and correlated errors. Simultaneous measurements were performed on two coupled charge-sensitive devices, revealing background tunneling rates at the single-hertz level with temporal resolution of tens of microseconds. Analysis of these events demonstrated that individual tunneling instances are uncorrelated, but bursts of activity occur approximately once per minute and exhibit strong correlation between the devices. These bursts, lasting around 7 milliseconds, induce a substantial thousand-fold increase in the quasiparticle tunneling rate across both devices, and a rarer subset also causes a shift in the offset charge. This practical and extensible method allows identification of quasiparticle bursts, their correlations, and spatial structure, thereby facilitating the development of strategies to suppress correlated errors in superconducting quantum processors. The technique’s sensitivity surpasses existing approaches reliant on coherence-time degradation, and its compatibility with superconducting qubits enables exploration of mitigation strategies like gap engineering and phonon-trapping techniques. The authors acknowledge a limitation in that the current study focuses on two devices, and scaling this method to larger qubit arrays will require further development. Future research will likely focus on implementing this real-time detection system in larger quantum processors to assess the effectiveness of various error mitigation strategies. These findings establish a valuable diagnostic framework for correlated error mechanisms, representing a crucial step towards achieving fault-tolerant superconducting quantum computation. 👉 More information 🗞 Real-time detection of correlated quasiparticle tunneling events in a multi-qubit superconducting device 🧠 ArXiv: https://arxiv.org/abs/2602.01945 Tags: