Tunable Couplers with High On-Off Ratio Based on Floating Transmons

Recent implementations of surface code-based error correction [1] suggest that the infidelity of two-qubit gates accounts for a significant portion of the logical error, which highlights the importance of exploring novel coupling elements and gate schemes. Here, we present progress towards designing and implementing a floating transmon-based qubit-coupler element, which aims to function as a primitive cell that can be easily replicated in transmon lattices, thereby ensuring scalability. The chosen coupler design eliminates the need for direct inter-qubit capacitive coupling, and the flux-tunable Josephson circuit is optimized to enhance the on-off ratio. Numerical simulations suggest that these design choices aid in suppressing residual ZZ interactions while ensuring strong inter-qubit coupling at the gate implementation frequency [2].

Ref:

[1]: R. Acharya et al., arXiv preprint arXiv: 2408.13687 (2024)

[2]: M. C. Collodo et al., Physical review letters, 125(24), 240502 (2020)