Paper detail

Single-Step Hybrid CV-DV Transfer of Multipartite W States Using Cat-State Qubits

We propose a deterministic hybrid continuous-variable-discrete-variable (CV-DV) scheme for the single-step transfer of an $n$-qubit W state encoded in photonic Schr$\ddot{o}$dinger cat-state qubits within a circuit QED architecture. Logical qubits are encoded in even- and odd-parity cat states of bosonic modes, while effective Raman-type interactions between resonator pairs are mediated by a single superconducting flux qutrit operating in the dispersive regime. The protocol coherently transfers the multipartite W state in a single collective operation without populating higher excited atomic levels, thereby strongly suppressing decoherence. Numerical simulations based on the full Lindblad master equation, including realistic cavity dissipation, qutrit relaxation and dephasing, and inter-cavity crosstalk, show that a three-qubit cat-state W state can be transferred with a maximum fidelity of approximately $0.92$. These results demonstrate the feasibility of scalable hybrid CV-DV entanglement transfer using current circuit QED technology.