Laser annealing enabled resistance reduction and stable frequency tuning of superconducting qubits

Abstract

The scalability of superconducting quantum processors is hindered by frequency collisions among qubits, calling for precise and reliable frequency tuning techniques. Here, we develop a laser annealing platform and systematically investigate its effect on superconducting qubits. In contrast to previous reports that consistently observed an increase in the Josephson junction resistance Rn, we find that laser annealing can also reduce Rn by up to 24.9%, corresponding to a significant increase in qubit frequency with a tuning precision of 22.8 MHz. This complementary behavior enriches the phenomenology of laser annealing. Atomic-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy analysis reveal a reduced Al coordination number and an increased oxygen vacancy concentration, which lower the effective barrier height and account for the decrease in Rn. Importantly, laser-annealed qubits maintain high coherence, and storage at −10 °C in high vacuum suppresses long-term resistance drift to below 0.5%. These results demonstrate that laser annealing provides a practical approach for stable and accurate frequency tuning. Beyond this, our findings suggest that the effect of laser annealing is richer than previously recognized and leave open the possibility of developing more versatile, potentially bidirectional frequency control for scalable superconducting quantum processors.