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Scientific Reports

Heralded interconversion between hyperentangled W state and hyperentangled KLM state assisted by nitrogen vacancy centers coupled with microresonators

Fang‐Fang Du, Ming Ma, Qiulin Tan

Published Jan 20, 2025• 12 citations
Publisher

Abstract

As the hyperentanglement of photon systems holds lots of remarkable applications for enhancing channel capacity with less quantum resource, the interconversion of various hyperentangled states warrants in-depth investigation and becomes a vital work for quantum information technologies. Here we realize completely mutual conversions between spatial-polarization hyperentangled Knill-Laflamme-Milburn state and hyperentangled W state for three-photon systems, resorting to hyperparallel quantum control gates and the practical nonlinear interaction of nitrogen-vacancy centers coupled with whispering-gallery-mode microresonators. The hyperparallel quantum gates, i.e., hyperparallel controlled-not and controlled-swap gates, are fundamental prerequisites for realizing interconversions of two hyperentangled states in a deterministic way. The fidelities of these conversion processes are robust and their efficiencies are also high due to fewer nonlinear interactions and errors heralded by the response of detectors, which intensify comprehending the properties of hyperentanglement.

DOI
10.1038/s41598-025-85673-0

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As the hyperentanglement of photon systems holds lots of remarkable applications for enhancing channel capacity with less quantum resource, the interconversion of various hyperentangled states warrants in-depth investigation and becomes a vital work for quantum information technologies. Here we realize completely mutual conversions between spatial-polarization hyperentangled Knill-Laflamme-Milburn state and hyperentangled W state for three-photon systems, resorting to hyperparallel quantum control gates and the practical nonlinear interaction of nitrogen-vacancy centers coupled with whispering-gallery-mode microresonators. The hyperparallel quantum gates, i.e., hyperparallel controlled-not and controlled-swap gates, are fundamental prerequisites for realizing interconversions of two hyperentangled states in a deterministic way. The fidelities of these conversion processes are robust and their efficiencies are also high due to fewer nonlinear interactions and errors heralded by the response of detectors, which intensify comprehending the properties of hyperentanglement.
Abstract In the paper, the possibility of two complete conversions is investigated, one is from the two‐photon hyperentangled Knill–Laflamme–Milburn (KLM) state to hyperentangled Bell states, the other is from three‐photon KLM state to the hyperentangled Greenberger–Horne–Zeilinger states, for photonic systems hyper‐encoded in polarization and spatial degrees of freedom assisted by error‐heralded quantum units (EHQUs). The system inhomogeneity and/or the imperfect photon scattering often restrict the performance of effective conversions of two types of hyperentangled states, and result in the reductions of the fidelity and the efficiency in tangible quantum information technologies. The polarization EHQU and spatial EHQU are two critical tools for actualizing two hyperentangled conversions in a heralded way, as the errors stemming from the system inhomogeneity and practically imperfect scattering are converted into efficacious responses of the detectors in our protocols. Thus, the fidelities of these conversion cases keep unchanged and have close to unity fidelities, which deepen the understanding of the properties of hyperentanglement.
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.
Abstract The generation, fusion, and interconversion of quantum entangled states play equally important roles in quantum information processing. In this paper, we propose a deterministic protocol to realize the interconversion between the three-electron-spin W state and the Knill–Laflamme–Milburn state by exploiting controlled quantum gates and parity-measuring devices constructed via the interaction between a photon and electron spins in silicon-vacancy system. Our analysis reveals that, considering non-ideal factors, both conversions achieve high fidelities and efficiencies. The efficient interconversion of stationary entangled states contributes to a deeper understanding of quantum entanglement and significantly contributes to quantum information processing
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 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.
Encoding computing qubits in multiple degrees of freedom (DOFs) of a photonic system allows hyperparallel quantum computation to enlarge channel capacity with less quantum resource, and constructing high-fidelity hyperparallel quantum gates is always recognized as a fundamental prerequisite for hyperparallel quantum computation. Herein, we propose an approach for implementing a high-fidelity photonic hyperparallel controlled-phase-flip (CPF) gate working with polarization, spatial-mode, and frequency DOFs, through utilizing the practical interaction between the single photon and the diamond nitrogen vacancy (NV) center embedded in the cavity. Particularly, the desired output state of the gate without computation errors coming from the practical interaction is obtained, and the robust fidelity is guaranteed in the nearly realistic condition. Meanwhile, the requirement for the experimental realization of the gate is relaxed. In addition, this approach can be generalized to complete the high-fidelity photonic three-DOF hyperparallel CPFN gate and parity-check gate. These interesting features may make the present scheme have potential for applications in the hyperparallel quantum computation.