Qubit errors traced to two sources, cosmic rays, cooler vibrations

Correlated errors, accounting for an unspecified percentage of errors in superconducting qubits, are now being distinguished as originating from two distinct sources, a surprising finding that moves beyond simply detecting errors to understanding their origins. Researchers at the Massachusetts Institute of Technology have linked these errors to both ionizing radiation from cosmic and terrestrial sources and to mechanical vibrations from the pulse tube within dilution refrigerators. The work presents a method for differentiating these error types by examining their temporal, spatial, and frequency characteristics, potentially enabling targeted error-mitigation strategies.

The team also found that engineering the superconducting gap across Josephson junctions reduces the rate of errors from both radiation and vibrations. They measured arrays of qubits with varying superconducting gap differences, where the difference in superconducting gap was less than and greater than the qubit frequency. Operating in a different dilution refrigerator with a different mass and structural configuration reduced the vibration-induced errors. The researchers linked the errors to pulse tube operation, but did not observe a complete cessation of the errors when the pulse tube was switched off.

Cosmic Ray Impact on Superconducting Qubit Decoherence Cosmic rays are identified as one source of these correlated errors, a previously underappreciated factor impacting the stability of superconducting qubits, suggesting shielding may be a key area for improvement. High-energy particles impacting the qubit device and its substrate generate quasiparticles, which then tunnel across Josephson junctions, critical components of the qubit, and induce errors. These errors are not isolated events; they can persist for tens of milliseconds and simultaneously affect multiple qubits in close proximity, creating challenges for quantum error correction. The research team measured arrays of transmon qubits, investigating devices where the difference in superconducting gap across the Josephson junction was both less than and greater than the qubit energy. Beyond external radiation, vibrations within the dilution refrigerator, the cooling system maintaining the extremely low temperatures needed for qubits, are pinpointed as the second major source of correlated errors, indicating that even seemingly isolated quantum systems are susceptible to mechanical disturbances. Specifically, the pulse tube cryocooler, used to pre-cool the dilution refrigerator, induces periodic vibrations that correlate with increased error rates. Accelerometer data confirmed the link between these vibrations and the observed errors, and the team found that operating in a different dilution refrigerator with a different mass and structural configuration reduced the vibration-induced errors. Quasiparticle Tunneling & Josephson Junction Errors Superconducting qubit performance is increasingly limited by errors that affect multiple qubits simultaneously, a challenge for building practical quantum computers. This detailed understanding moves beyond simply detecting errors to pinpointing their source. Measurements were conducted on three devices.

The team measured arrays of qubits with varying superconducting gap differences, specifically those where the difference in superconducting gap was less than the qubit frequency and those where it was greater, to assess the characteristics of the errors. Devices engineered with a larger difference in the superconducting gap across the Josephson junction exhibited a reduced rate of both radiation- and pulse tube-induced errors. This finding suggests that gap engineering, increasing the difference in superconducting gap to be greater than the qubit frequency, offers a protective effect against both types of correlated errors. Temporal and Spatial Characteristics of Correlated Errors This variance underscores the importance of considering the mechanical stability of the experimental setup, as even subtle vibrations can introduce correlated errors. The study’s ability to distinguish between error types based on their temporal, spatial, and frequency characteristics provides a powerful tool for diagnosing and addressing decoherence in complex quantum systems.

Distinguishing Error Types via Frequency Domain Features The team’s analysis revealed that the temporal, spatial, and frequency characteristics of errors stemming from cosmic and terrestrial radiation differed significantly from those induced by pulse tube vibrations. Accelerometer data directly correlated the vibrations with the observed errors, providing a physical link between the refrigerator’s operation and qubit decoherence. This correlation was further substantiated by comparing data from two different dilution refrigerators, each with unique mass and structural configurations, where the errors were reduced. Further investigation focused on the superconducting gap across Josephson junctions, a design element known to reduce radiation-induced errors. This approach enabled the team to present a method for distinguishing error types, a crucial step toward developing physically motivated error-mitigation strategies and improving the reliability of future quantum computations.

Pulse Tube Vibrations as a Correlated Error Source Mechanical disturbances originating from the cooling systems essential to superconducting qubit operation represent a previously underappreciated source of error, according to work from the Massachusetts Institute of Technology. While cosmic rays have long been recognized as a factor inducing correlated errors, those impacting multiple qubits simultaneously, researchers have now definitively linked vibrations from pulse tube cryocoolers to a distinct population of these errors.

The team’s investigation involved detailed measurements of three devices, each containing arrays of transmon qubits. Notably, the pulse tube-induced errors were linked to pulse tube operation, providing a clear causal link. Accelerometer data directly corroborated this connection, demonstrating a strong correlation between the vibrations generated by the pulse tube and the observed error rates in the qubits. Further substantiation came from comparative measurements conducted using two different dilution refrigerators, each possessing a unique mass and structural configuration, resulting in differing vibration profiles. This suggests that even seemingly isolated quantum systems remain susceptible to external mechanical influences. The study also examined devices engineered with varying superconducting gap profiles across their Josephson junctions, a design element previously shown to mitigate radiation-induced errors. The reduction in both error types in these devices underscores the potential for a unified approach to improving qubit resilience.

Accelerometer Data Correlates Vibrations to Qubit Errors The investigation extended beyond simply identifying the sources of error; the team sought to understand the mechanical environment influencing qubit performance. This comparative approach was critical, as the researchers found that operating in a different dilution refrigerator with a different mass and structural configuration reduced the vibration-induced errors. Devices with a larger superconducting gap, where the difference in gap exceeds the qubit energy, exhibited a reduction in both types of errors.

Superconducting Gap Engineering Mitigates Radiation Effects Massachusetts Institute of Technology researchers identified two primary contributors: ionizing radiation and mechanical vibrations induced by the pulse tube within dilution refrigerators. Measurements focused on arrays of transmon qubits, comparing those with a superconducting gap difference across the junction less than the qubit energy to those where the gap difference exceeded it. This gap engineering approach, previously demonstrated to reduce radiation-induced errors, proved effective against vibrations as well. The researchers present a method for differentiating these two types of errors by their temporal, spatial, and frequency domain features. Accelerometer data confirmed differing vibration environments between the two systems. This correlation was established through accelerometer data, which linked vibrations to the errors. The ability to distinguish between radiation-induced and vibration-induced errors, coupled with the effectiveness of gap engineering, offers a promising pathway towards building more robust and reliable quantum computing systems. δΔ_(JJ) Parameter & Qubit Frequency Relationship Massachusetts Institute of Technology researchers are meticulously characterizing the interplay between superconducting gap engineering and correlated error rates in transmon qubits, a crucial step toward building more stable quantum processors.

The team’s investigation revealed that manipulating this gap, specifically ensuring the difference in superconducting gap exceeds the qubit frequency, significantly reduces both radiation-induced and vibration-induced errors. This finding expands upon previous research demonstrating the effectiveness of gap engineering against radiation, now extending its protective capabilities to mechanical disturbances. Researchers linked the errors to the operation of the pulse tube, a pre-cooling system, and confirmed this connection through accelerometer data. Measurements across the three devices showed a clear correlation between pulse tube vibrations and the observed error rates, with the magnitude of the errors fluctuating in sync with the cooler’s cyclical operation. Further analysis revealed that devices engineered with a larger superconducting gap difference exhibited lower rates of both error types. This suggests a common underlying mechanism by which both radiation and vibrations contribute to qubit errors, potentially involving quasiparticle tunneling across the Josephson junctions. 👉 More information🗞 Distinguishing types of correlated errors in superconducting qubits✍️ H. P. Binney et al.🧠 DOI: http://link.aps.org/doi/10.1103/j235-47t6 Stay currentSee today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals. Tags: