Single Flux Quantum-Based Superconducting Qubit Control and Quasiparticle Mitigation: Part 2*

The Single Flux Quantum (SFQ) digital logic family has been proposed as a scalable approach for the control of next-generation multiqubit arrays. In an initial implementation, the fidelity of SFQ-based qubit gates was limited by quasiparticle (QP) poisoning induced by the dissipative SFQ driver. Here we introduce superconducting bandgap engineering as a mitigation strategy to suppress QP poisoning in this system. We explore low-gap moats and high-gap fences surrounding the qubit structure, along with a geometry involving extensive coverage of the high-gap groundplane with low-gap traps. We use charge-sensitive transmon qubits to evaluate the effectiveness of the various mitigation strategies in experiments involving direct QP injection.