Tunable Nonlocal Interaction for Remote Controlled-Z Gates Between Distributed Fixed-Frequency Qubits
arXiv:2603.28526
The paper proposes a modular superconducting quantum processor architecture that uses double‑transmon couplers and a 25‑cm coaxial cable to create a tunable nonlocal ZZ interaction, enabling high‑fidelity remote controlled‑Z gates between fixed‑frequency qubits.
Abstract
Scaling superconducting quantum processors toward fault-tolerant operation will likely require architectures that extend beyond monolithic chips. Modular processors connected by low-loss superconducting links provide a promising route, but implementing entangling gates between remote fixed-frequency qubits remains challenging. Here we propose a distributed architecture in which two synchronously controlled double-transmon couplers mediate the interaction between fixed-frequency transmons in separate packages connected by a 25-cm coaxial cable. The scheme activates a tunable nonlocal interaction on demand while suppressing residual static coupling, allowing the superconducting link to function as a gate-native interconnect rather than solely as a state-transfer channel. Circuit-level simulations show an on/off ratio exceeding and a remote controlled-Z gate with a projected coherent fidelity of under experimentally relevant parameters. Open-system simulations further indicate that, within the representative Markovian noise model considered here, endpoint-qubit decoherence is the largest contribution to gate infidelity, while photon loss in the retained cable modes remains smaller but non-negligible. These results identify DTC-mediated tunable nonlocal coupling as a promising gate primitive for modular superconducting processors based on fixed-frequency qubits.
22 pages, 5figures