ABSTRACT W states are essential resources in quantum communication and computation but are highly vulnerable to decoherence. We propose a three‐stage, non‐recursive entanglement distillation protocol that extracts a maximally entangled W state from multiple copies of amplitude‐damped W states, applicable to both the standard and generalized W states. Unlike conventional recursive schemes, the proposed protocol imposes no constraints on the initial fidelity of the input states and achieves unit‐fidelity distillation with improved efficiency and success probability. Instead of iteratively enhancing entanglement fidelity, our approach constructs a specific non‐trivial sacrificial‐state structure within the first two stages of the protocol. By sacrificing this intermediate state in the final stage, the protocol enables the distillation of a maximally entangled W state from an amplitude‐damped input, offering a new non‐recursive route to high‐fidelity multipartite entanglement purification. Comparative analysis demonstrates that the proposed method significantly outperforms the weak‐measurement‐based distillation protocol across all decay rates. The IBM Qiskit simulations further validate the analytical predictions, confirming both the correctness and the practical feasibility of the proposed protocol.
ABSTRACT W states are essential resources in quantum communication and computation but are highly vulnerable to decoherence. We propose a three‐stage, non‐recursive entanglement distillation protocol that extracts a maximally entangled W state from multiple copies of amplitude‐damped W states, applicable to both the standard and generalized W states. Unlike conventional recursive schemes, the proposed protocol imposes no constraints on the initial fidelity of the input states and achieves unit‐fidelity distillation with improved efficiency and success probability. Instead of iteratively enhancing entanglement fidelity, our approach constructs a specific non‐trivial sacrificial‐state structure within the first two stages of the protocol. By sacrificing this intermediate state in the final stage, the protocol enables the distillation of a maximally entangled W state from an amplitude‐damped input, offering a new non‐recursive route to high‐fidelity multipartite entanglement purification. Comparative analysis demonstrates that the proposed method significantly outperforms the weak‐measurement‐based distillation protocol across all decay rates. The IBM Qiskit simulations further validate the analytical predictions, confirming both the correctness and the practical feasibility of the proposed protocol.
In this work, we study how to distill two typical multipartite entangled noisy states, the amplitude-damped W state and the amplitude-damped Greenberger-Horne-Zeilinger state. Unlike the currently existing multipartite entanglement purification schemes, our scheme is a single-copy-based scheme, i.e., only one noisy state is needed in each distillation round, and the complicated multilateral controlled-not (cnot) operations are replaced by measurements of local positive-operator-valued measures (POVMs). The results show that local POVM measurements on one copy of the noisy state can project the initial state onto a new state with higher entanglement and nonlocality. In this scheme, although the final state can violate the multipartite Bell inequality, the corresponding initial noisy state does not violate it, which means that this distillation scheme can reveal the hidden genuine multipartite nonlocality of these initial states. For the case of the amplitude-damped W state, if the POVM parameters are appropriately chosen, the fidelity of the output state can approach 1.0 for all the initial states with fidelity bigger than zero. So this single-copy-based multipartite entanglement distillation scheme has a wide range of distillable fidelities, and it is much simpler than the two-copy- or multiple-copy-based schemes. Furthermore, if the POVM measurement is carried out only on some member qubits rather than all of them, the distillation scheme can succeed too, which will greatly decrease the implementation complexity of the scheme. So this multipartite entanglement distillation scheme may be implementable in some physical system.
Entanglement distillation, the process of converting weakly entangled states into maximally entangled ones using Local Operations and Classical Communication (LOCC), is pivotal for robust entanglement-assisted quantum information processing in error-prone environments. A construction based on stabilizer codes offers an effective method for designing such protocols. By analytically investigating the effective action of stabilizer protocols for systems of prime dimension d , we establish a standard form for the output states of recurrent stabilizer-based distillation. This links the properties of input states, stabilizers, and encodings to the properties of the protocol. Based on those insights, we present a novel two-copy distillation protocol, applicable to all bipartite states in prime dimension, that maximizes the fidelity increase per iteration for Bell-diagonal states. The power of this framework and the protocol is demonstrated through numerical investigations, which provide evidence for superior performance in terms of efficiency and distillability of low-fidelity states compared to other well-established recurrence protocols. By elucidating the interplay between states, errors, and protocols, our contribution advances the systematic development of highly effective distillation protocols, enhancing our understanding of distillability.
Abstract Ideal deterministic quantum communication tasks require maximally entangled channels. The reality is that the maximally entangled channel is inevitably degraded to a generally entangled one because of various decoherence mechanisms, seriously deteriorating the performance of quantum communication. In most cases, entanglement purification and distillation are utilized to improve the entanglement and to construct the maximally entangled channel. In this paper, we proposed an alternative scheme to realize deterministic joint remote state preparation using a non-maximally entangled channel. Instead of spending additional entanglement resources in advance for entanglement purification or distillation, only two non-entangled ancillaries are employed in this scheme. Whether the employed quantum channel is a maximally entangled channel or a generally entangled one, remote state preparation would never fail theoretically in this investigation. This protocol provides a feasible way for the construction of practical quantum networks.
Abstract Maximally entangled states are crucial for various quantum information processing, yet their quality suffers from entanglement loss due to decoherence. In this paper, a direct purification technique that utilizes weak measurement and requires only two copies of the entangled state is proposed. The method involves transforming the damped entangled state with weak measurements and then applying a direct purification process. This approach yields a maximally entangled state with a certain probability. In the context of Bell state purification, two weak measurement‐based operations designed to convert amplitude‐damped Bell states into the desired state for direct purification method are presented. The first operation is applied prior to the noisy channel, while the second is employed after the noisy channel. Through comprehensive analysis, the performances of these two schemes are evaluated and compared and benchmarked them against a pioneering weak measurement‐based scheme. The findings demonstrate that the proposed methods exhibit superior performance in terms of both fidelity and probability. Additionally, a novel technique for purifying multipartite amplitude‐damped Greenberger–Horne–Zeilinger (GHZ) states is introduced, which existing methods cannot address. By employing only two copies of the entangled states and harnessing the unique advantages of weak measurement operations, the method achieves both resource efficiency and effectiveness.
High-fidelity entanglement shared between distant quantum systems is an essential resource for quantum communication and computation. Entanglement distillation addresses this need by converting multiple noisy Bell pairs into fewer higher-fidelity pairs, using only local quantum operations and classical communication. However, this approach typically requires a substantial overhead in the number of qubits. To bypass this hurdle, we propose to leverage the high-dimensional Hilbert space of a single pair of bosonic systems to store a large amount of entanglement, replacing the need for multi-qubit systems. To distill entanglement in such a setup, we devise a new entanglement distillation protocol, tailored for bosonic systems. The protocol converts a highly-entangled noisy state between two bosonic systems into a lower-dimensional but high-fidelity entangled state, using only local bosonic operations. We show that our protocol significantly enhances the fidelity of the entangled state in the presence of naturally occurring loss and dephasing errors. Compared to methods relying on multiple Bell pairs, our scheme offers a more hardware-efficient strategy, providing a practical route toward the realization of entanglement distillation.
In this paper, we propose a deterministic entanglement swapping protocol for generating a shared three-qubit W state between two remote parties. Our method offers a reliable alternative to existing probabilistic protocols for W state entanglement swapping, which is crucial for various quantum information processing tasks. We present a detailed quantum circuit design, implemented using the Qiskit simulator, that outlines the preparation of W states and the execution of joint measurements required for the entanglement swapping process. Furthermore, we analyze the effects of imperfect operations and noisy communication channels on the fidelity of the resulting shared W state. To address these challenges, we introduce a weak measurement-based purification method that enhances fidelity in the presence of amplitude damping. Through mathematical analysis and Qiskit simulations, we demonstrate the effectiveness of our proposed protocol, offering a practical solution for high-fidelity W state generation in real-world quantum communication scenarios.