Deterministic Kerr‐Effect‐Based Mutual Conversions of Entangled States in Decoherence‐Free Subspace

Mutual conversions between different entangled states play a significant role in quantum information processing (QIP), significantly boosting the versatility and robustness of quantum systems, and particularly paving the way for demanding specific entanglement forms. Reliable protocols are proposed for the deterministic mutual conversions between the three‐logic‐qubit W state and the three‐logic‐qubit Knill–Laflamme–Milburn state within a decoherence‐free subspace (DFS), which utilizes weak cross‐Kerr nonlinearity combined with X‐homodyne measurement. In‐depth analyses of both protocols confirm that they can achieve high fidelities and outstanding efficiencies by related feedback operations. Additionally, the protocols effectively suppress decoherence effects through the use of DFS, enabling the advanced development of practical QIP.