Mechanically induced correlated errors on superconducting qubits with relaxation times exceeding 0.4 ms

Abstract: Superconducting qubits are among the most advanced candidates for achieving fault-tolerant quantum computing. Despite recent significant advancements in the qubit lifetimes, the origin of the loss mechanism for state-of-the-art qubits is still subject to investigation. Furthermore, the successful implementation of quantum error correction requires negligible correlated errors between qubits. Here, we realize long-lived superconducting transmon qubits that exhibit fluctuating lifetimes, averaging 0.2 ms and exceeding 0.4 ms – corresponding to quality factors above 5 million and 10 million, respectively. We then investigate their dominant error mechanism. By introducing novel time-resolved error measurements that are synchronized with the operation of the pulse tube cooler in a dilution refrigerator, we find that mechanical vibrations from the pulse tube induce nonequilibrium dynamics in highly coherent qubits, leading to their correlated bit-flip errors. Our findings not only deepen our understanding of the qubit error mechanisms but also provide valuable insights into potential error-mitigation strategies for achieving fault tolerance by decoupling superconducting qubits from their mechanical environments.

 Conclusion：In summary, in this work, we presented a novel time-resolved measurement technique to study the mechanical sensitivity of long-lived transmon qubits, synchronized with the operation of the pulse tube cooler of a dilution refrigerator. Our results demonstrated that the mechanical vibrations generated by the pulse tube cooler induce dominant bit-flip errors in the qubits. Moreover, the global nature of the mechanical bursts on the multi-qubit device causes correlated errors among the qubits, which are detrimental to realizing large-scale quantum computing based on quantum error correction. While the origin of mechanical sensitivity of the qubits could not be established unequivocally, our observations are consistent with quasiparticle- and TLS-induced qubit decay models40,41, and provide valuable insights into the loss mechanisms that limit the state-of-the-art qubit coherence. 

Article：https://doi.org/10.1038/s41467-024-48230-3