A three qubit system with a common SQUID coupler with increased connectivity for fast gates

The majority of popular superconducting qubit system architectures employ pairwise nearest-neighbor (either fixed or tunable) couplings between qubits and individualized readout resonators. In these systems the localized nearest-neighbor connectivity can create complications for algorithm circuit decomposition requiring numerous SWAP operations. However, there are feasible alternative options to add increased qubit connectivity and shared control and readout resources benefitting scalability. With appropriate parameter choice and frequency allocation, groups of qubits with all-to-all connectivity can be achieved despite the challenge of the quadratic increase in the number of pairwise interactions with increasing qubit count. Our group has developed a design approach of this style consisting of multiple resonant modes, acting as either qubits or cavities, all galvanically coupled to a common tunable SQUID element. This enables high on/off coupling ratios and fast parametrically driven interactions for gates and readout. In this talk, we will review our design and simulation tools for this approach and discuss an example of a three qubit system with all-to-all connectivity. We will highlight some of the design and operational challenges and advantages of this system.