UC Berkeley

Superconducting circuits are a leading platform for quantum computation and quantum simulation. Interactions are typically mediated by pairwise coupling elements between nearest neighbor qubits. The development of tunable couplers has been essential to achieving high fidelity entangling gates alongside high fidelity single qubit gates in quantum processors. In quantum simulators, tunable coupling allows flexibility in emulating different systems and the exploration of different parameter regimes of those models in a single physical device. Distributed element circuitry has enabled long range coupling and leveraging of interference effects and spatial mode variations to enhance device performance. In this thesis I will discuss work towards developing a distributed element tunable coupling circuit: a transmission line cavity terminated by SQUIDs, which serve as flux tunable impedances, at either boundary. With this device we hope to integrate the dynamic programmability of interactions mediated by a tunable coupler with the long-range, multi-qubit coupling enabled by distributed transmission lines in a single system. We experimentally demonstrate the core functionality, including tunability of the coupling rates, programmability of the connectivity graph, and parallel operation via multiplexing. Additionally, we utilize this device to explore photon blockade effects in the Tavis-Cummings Model, highlighting the value of tunability and controllability when simulating novel light-matter interactions in highly connected systems. These results contribute to ongoing research towards designing, calibrating, and operating highly connected superconducting circuit systems. Devices with high connectivity enable more efficient circuit compilation and are useful as quantum routers in quantum networks. In recent years, understanding the role of connectivity in quantum error correction has emerged as an important research focus. There is ongoing work evaluating the tradeoff between performance and connectivity in real devices. The development of coupling architectures that enable denser and/or longer range connectivity will play a critical role in optimizing this tradeoff.