Improving coherence and stability of superconducting qubits by thermal annealing in vacuum

Superconducting qubits are prone to noise induced by material defects, which degrades their coherence and performance of gate operations. In this work, by thermally annealing a chip with 20 tunable transmon qubits in vacuum, we realize an approximate 30% enhancement in the average energy relaxation time T¯1 from 162 to 210 μs. After annealing, T¯1 also shows smaller fluctuations in time, and the aging of the qubits, when kept under ambient conditions, is remarkably decelerated. Our work demonstrates a simple yet highly effective way to improve the coherence and stability of superconducting qubits for scalable superconducting quantum processors.