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Optics Express

Decoherence-free-subspace-based deterministic conversions for entangled states with heralded robust-fidelity quantum gates

Fang‐Fang Du, Xue-Mei Ren, Zhi‐Guo Fan, Linghui Li, Xin‐Shan Du, Ming Ma, Gang Fan, Jing Hua Guo

Published Dec 19, 2023• 50 citations
Publisher

Abstract

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.

DOI
10.1364/oe.508088

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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 Hybrid entangled states are crucial in quantum physics, offering significant benefits for hybrid quantum communication and quantum computation, and then the conversion of hybrid entangled states is equally critical. This paper presents two novel schemes, that is, one converts the two-qubit hybrid Knill–Laflamme–Milburn (KLM) entangled state into Bell states and the other one transforms the three-qubit hybrid KLM state into Greenberger–Horne–Zeilinger (GHZ) states assisted by error-predicted and parity-discriminated devices. Importantly, the integration of single photon detectors into the parity-discriminated device enhances predictive capabilities, mitigates potential failures, and facilitates seamless interaction between the nitrogen-vacancy center and photons, so the two protocols operate in an error-predicted way, improving the experimental feasibility. Additionally, our schemes demonstrate robust fidelities (close to 1) and efficiencies, indicating their feasibility with existing technology.
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 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.
Abstract Quantum entanglement plays a crucial role in quantum information technologies. In the paper, we propose two schemes to convert from two-photon Knill–Laflamme–Milburn (KLM) entangled states to Bell states and three-photon KLM state to Greenberger–Horne–Zeilinger states based on error-detected quantum devices (EDQDs), which employ the interaction between a quantum-dot-cavity system and a photon. Moreover, the quantum circuits of EDQDs applied in the conversion processes make our schemes carry out faithfully, as the practical photon-scattering deviations are changed into heralded-failure detections. Analyses show that conversion cases have unity fidelities and high efficiencies, which encourage us to appreciate deeply fundamental properties of entanglement.
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.
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.