Trapping quasiparticles on superconducting qubits through double gap engineering.*

Non-equilibrium quasiparticles have been identified as a major decoherence source in superconducting qubits. Strategies to mitigate the quasiparticle loss are highly demanded. Based on the diffusion theory¹, we propose a double gap engineering model to analytically and numerically simulate the quasiparticle diffusion in the superconducting transmon qubit under realistic assumptions, and we quantitatively calculate the improvement of trapping efficiency with this technique. Based on this model, we explore new qubit architectures and demonstrate the improvement of qubit relaxation and dephasing times experimentally, compared to those for single gap engineered and regular transmon qubits.

¹R.-P. Riwar and G. Catelani. Efficient quasiparticle traps with low dissipation through gap engineering., Physical Review B, 14, 100 (2019)