Design, fabrication and characterization of multi-qubit devices for quasiparticle injection studies.

Quasiparticles generated from various sources induce decoherence, posing a significant challenge for superconducting qubit technology. Unlike transmon qubits, the exact extent to which fluxonium qubits are affected by quasiparticles remains underexplored. To compare quasiparticle effects in fluxonia against more thoroughly studied transmons, we design devices with both qubit types on the same chip. To probe the quasiparticle losses, we voltage bias Josephson junctions to inject pair-breaking phonons, producing quasiparticles. In this talk, we discuss the design choices we made with respect to matching fluxonium and transmon frequencies and ensuring strong flux dependence of the matrix elements. We report on our progress in fabricating and characterizing these multi-qubit devices. These design and fabrication considerations are generally applicable to hybrid multi-qubit arrays.