A densely connected SNAIL-based 6 qubit quantum module

Increasing the size of quantum machines imposes constraints on critical design parameters, including frequency crowding and coupling strength between the qubits and nonlinear couplers that make up the machine which in turn can affect gate fidelities. These constraints necessitate careful examination to balance performance and scalability. In the second part of this talk, we introduce a multi-module, six transmon qubit machine whose frequency stack has been designed using the tools presented in the first part of this talk [McKinney, et al., ArXiv: 2409.18262]. The 3D module contains 6 superconducting fixed-frequency transmon qubits that connected via 2 SNAIL couplers, which mediate qubit population swaps via 3 wave parametric conversion processes. We will show the effects of the engineered transmon-SNAIL coupling values on the 2-qubit iSWAP and √iSWAP gate fidelities. Additionally, we will investigate the ability to cancel spectator qubit gate errors in neighboring modules due to near misses in qubit frequencies by driving cancellation pulses on the spectator’s SNAIL coupler and compare them with model predictions. Finally, we will discuss the impacts of the static ZZ qubit interactions on the error budget module.