Heralded Conversion of Multi-Qubit Entangled States With Quantum Multiplexing

This paper constructs a quantum multiplexing system centered on the single-photon time-bin degree of freedom to investigate the heralded conversion schemes of multi-qubit states between distant quantum memories. By analyzing the input-output relationship between a single photon and an atom-cavity coupled system, we clarify the fundamental quantum memory unit enabling state conversion. Two kind of schemes for multi-qubit entangled state conversion are proposed: first, the conversion from an (Formula presented.) -qubit KLM state to a W state, where a cyclic iterative mechanism effectively enhances efficiency; second, the conversion from an (Formula presented.) -qubit W state to a GHZ state, which requires differentiated time-bin mode designs tailored for systems with odd or even numbers of qubits. Both schemes allow for heralded verification of conversion success through the detection response of the single-photon time-bin mode. Performance analysis shows that the conversion efficiency of these schemes is sensitive to the single-photon reflectance coefficient. The proposed schemes can achieve high-fidelity conversion under currently feasible experimental parameters, and the quantum memory unit can be implemented in various quantum systems, such as atoms, nitrogen-vacancy centers, and silicon-vacancy centers.