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Advanced Quantum Technologies

Faithful Interconversions of Three‐Logic‐Qubit Entangled States Via Error‐Predicted Module in Decoherence‐Free Subspace

Ling‐Hui Li, Fang‐Fang Du

Published Jun 25, 2025• 4 citations
Publisher

Abstract

Abstract The interconversion between different types of entangled states is an essential process. It is particularly important for tasks requiring specific forms of entanglement, as it greatly enhances the versatility, robustness, and efficiency of quantum systems. In the paper, deterministic schemes are proposed for interconversion between three‐logic‐qubit W state and three‐logic‐qubit Knill‐Laflamme‐Milburn state within a decoherence‐free subspace (DFS). The process of mutual transformation leverages the state‐selective nature of a quantum dot (QD) confined in a double‐sided microcavity, along with high‐fidelity, error‐predictable quantum control gates. Furthermore, the incorporation of single‐photon detectors helps to identify and mitigate potential failures arising from imperfect interactions between photons and the QD‐cavity system, thereby significantly enhancing experimental viability. In‐depth analyses of both protocols confirm that they can, in principle, achieve near‐unit fidelities and outstanding efficiencies. Additionally, the protocols offer advanced solutions to decoherence challenges through the use of DFS, paving the way for the development of practical quantum technologies.

DOI
10.1002/qute.202500188

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Abstract The interconversion of a variety of entangled states can facilitate the information transmission and decline the risk of error rates. Here two faithful protocols to achieve deterministic interconversion between three‐logic‐qubit W state and three‐logic‐qubit Greenberger–Horne–Zeilinger state in decoherence‐free subspace (DFS), resorting to the state‐selective property of the quantum dot (QD)‐cavity systems and robust‐fidelity quantum control gates are presented. Moreover, the single‐photon detectors introduced can effectively herald and mitigate potential failures from imperfect interaction between the QD‐cavity system and photons, significantly enhancing experimental feasibility. Through comprehensive analysis and evaluation, the protocols demonstrate exceptional conversion efficiencies and deliver near‐perfect fidelities. Additionally, the DFS makes system coherence over extended periods to overcome the decoherence effect caused by specific environmental noise, paving the way for quantum information processing.
Abstract 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.
The decoherence-free subspace (DFS) serves as a protective shield against certain types of environmental noise, allowing the system to remain coherent for extended periods of time. In this paper, we propose two protocols, i.e., one converts two-logic-qubit Knill-Laflamme-Milburn (KLM) state to two-logic-qubit Bell states, and the other converts three-logic-qubit KLM state to three-logic-qubit Greenberger-Horne-Zeilinger states, through cavity-assisted interaction in DFS. Especially, our innovative protocols achieve their objectives in a heralded way, thus enhancing experimental accessibility. Moreover, single photon detectors are incorporated into the setup, which can predict potential failures and ensure seamless interaction between the nitrogen-vacancy center and photons. Rigorous analyses and evaluations of two schemes demonstrate their abilities to achieve near-unit fidelities in principle and exceptional efficiencies. Further, our protocols offer progressive solutions to the challenges posed by decoherence, providing a pathway towards practical quantum technologies.
Abstract The interconversion of different types of entangled states not only can realize the information transmission but also play a significant role in quantum information technologies, including increasing scalability and computational power, and reducing error rates. Here, two protocols for achieving a complete interconversion between W state and Knill–Laflamme–Milburn state assisted by the quantum dot (QD)‐cavity systems and common quantum control gates are proposed. In particular, the protocols employ a heralded approach strategically designed to predict potential failures and facilitate seamless interaction between the QD‐cavity system and photons with the help of a single photon detectors, enhancing experimental accessibility. Through extensive analyzes and evaluations of two protocols, the proposed two protocols achieve remarkable utilization rates of photons (i.e., unit in principle) and achieve near‐unit fidelities and high efficiencies in principle.
Abstract In the process of quantum information processing, decoherence effect caused by the coupling between system and its environment will no doubt lead to the error of quantum information stored in the system. To decrease the influence of decoherence effect, decoherence‐free subspace (DFS) is introduced. In this work, several schemes to convert the polarized‐entangled Knill–Laflamme–Milburn (KLM) states into Greenberger–Horne–Zeilinger (GHZ) states in DFS by using the weak cross‐Kerr nonlinearity are proposed. Numerical analysis shows that the proposed schemes have high fidelity and success probability. Due to the unique applications of multi‐qubit quantum entangled states in quantum information processing and the robust feature of DFS, the proposed schemes may play positive roles in the future development of quantum communication and quantum information processing tasks.
Abstract Quantum entanglement is a cornerstone in the development of quantum information technology. In this paper, we propose two deterministic approaches for interconversion between the Λ-type three-atom Knill–Laflamme–Milburn (KLM) entangled state and the three-atom W state. Interconversion requires error-manifested parity-check gates (EMPCGs), leveraging interactions between the Λ-type atom–cavity system and an auxiliary photon. Additionally, the quantum circuit of the EMPCG ensures predictable function by transforming practical imperfections from photon scattering into failure-heralded detection events. Our analysis demonstrates that two reversible conversions not only achieve robust fidelity but also maintain high efficiency, thereby providing deeper insights into the fundamental nature of entanglement.