Logical iSWAP gate between two dual-rail qubits

Realizing fault-tolerant quantum computation requires scalable quantum error correction (QEC). Error-correcting codes exploiting qubits with biased-noise exhibit more relaxed fault-tolerance thresholds. A promising realization of such a biased-noise qubit is the superconducting cavity–based dual-rail qubit, in which logical states are encoded in the single-excitation manifold (|01> and |10>) of two cavities. Here, we propose a logical iSWAP gate between two dual-rail qubits based on the interaction with a flux-tunable coupling element, which does not rely on the excitation of an additional anharmonic element. By carefully leveraging the dispersive shifts of the individual cavities using a fast flux pulse on the coupler, the states |10,01> and |01,10> of the dual-rail qubit hybridize. Further optimizing the flux pulse parameters enables the control of the phases imprinted on the |10,10> and |01,01> states inside the logical dual-rail space, effectively implementing a logical iSWAP operation. We numerically investigate the dependence of the gate performance on system parameters and show that experimentally feasible parameters produce gate fidelities above 99.9% with gate times below 350 ns, demonstrating a fast and high-fidelity gate for architectures based on cavity dual-rail qubits.