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arXiv:2512.24274

Deterministic distribution of W-class states in quantum networks

Souvik Chatterjee, Prasenjit Deb, Chandan Datta, Pankaj Agrawal

quant-phSubmitted Dec 30, 2025• Announced Dec 31, 2025• 0 citations
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Abstract

Multipartite entangled states possess a number of non-intuitive properties, making them a useful resource for various quantum information-processing tasks. The three-qubit W-state is one such example where every state is robust to single-qubit loss. However, this state is not suitable for deterministic distribution, and deterministic communication protocols. Here, we focus on the distribution of a non-symmetric version of such states, namely $W_{\mathrm{mod}}$ states. These states belong to the W-class, and have one ebit of entanglement across a specific bipartition, enabling deterministic teleportation and superdense coding. In particular, we describe a few protocols through which these multipartite entangled states can be distributed {\it deterministically} in a quantum network by first preparing them locally in a central node and then transmitting individual qubits to the end nodes. We analyse the performance of these protocols based on the fidelity of the final distributed state, considering all types of noises that can act during the distribution. Finally, we compare the performance of the protocols to the case where the distribution is performed without any central node.

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Multipartite entangled states possess a number of non-intuitive properties, making them a useful resource for various quantum information-processing tasks. The three-qubit W-state is one such example where every state is robust to single-qubit loss. However, this state is not suitable for deterministic distribution, and deterministic communication protocols. Here, we focus on the distribution of a non-symmetric version of such states, namely WmodW_{\mathrm{mod}}Wmod​ states. These states belong to the W-class, and have one ebit of entanglement across a specific bipartition, enabling deterministic teleportation and superdense coding. In particular, we describe a few protocols through which these multipartite entangled states can be distributed {\it deterministically} in a quantum network by first preparing them locally in a central node and then transmitting individual qubits to the end nodes. We analyse the performance of these protocols based on the fidelity of the final distributed state, considering all types of noises that can act during the distribution. Finally, we compare the performance of the protocols to the case where the distribution is performed without any central node.
We study the performance (rate and fidelity) of distributing multipartite entangled states in a quantum network through the use of a central node. Specifically, we consider the scenario where the multipartite entangled state is first prepared locally at a central node and then transmitted to the end nodes of the network through quantum teleportation. As our first result, we present leading-order analytical expressions and lower bounds for both the rate and fidelity at which a specific class of multipartite entangled states, namely, Greenberger-Horne-Zeilinger (GHZ) states, are distributed. Our analytical expressions for the fidelity accurately account for time-dependent depolarizing noise encountered by individual quantum bits while stored in quantum memory, as verified using Monte Carlo simulations. As our second result, we compare the performance to the case where the central node is an entanglement switch and the GHZ state is created by the end nodes in a distributed fashion. Apart from these two results, we outline how the teleportation-based scheme could be physically implemented using trapped ions or nitrogen-vacancy centers in diamond.
This thesis takes a deep dive into quantum resources and their applications for quantum networks. In particular, this work reviews the concept of quantum correlations beyond entanglement and introduces a method for deterministically creating them via local operations by using classical correlations as a resource. The structure of these states is analysed in multipartite quantum networks, highlighting their generally asymmetric nature. We then explore how these quantum correlations can be used for entanglement generation protocols themselves and compare them to directly distributing a maximally entangled state through noisy channels. We find that, in certain noise regimes, these protocols can indeed outperform direct entanglement distribution, provided the memories at each node are sufficiently maintained. The application of multipartite quantum teleportation to multiple receivers in a network is also assessed, exploring the necessary and sufficient resources to ensure that the performance of quantum telecloning surpasses that of all known methods involving only classical communication. Our results show that, despite the genuine multipartite entanglement present in the resource state, only a few bipartite entanglement pairings are necessary for such a feat. This allows for a potential reduction in resource consumption for future experimental implementations. Thesis is embargoed until 31 December 2026.
The generation of entanglement across different nodes in distributed quantum architectures plays a pivotal role for different applications. In particular, deterministic, robust, and fast protocols that prepare genuine multipartite entangled states are highly desirable. In this article, we propose a fractional quantum state transfer, in which the excitation of an emitter is partially transmitted through the quantum communication channel and then absorbed at a spatially separated node. This protocol is based on wavepacket shaping allowing for a fast deterministic generation of Bell states among two quantum registers and WWW states for a general setting of NNN qubits, either in a sequential or simultaneous fashion, depending on the topology of the network. By means of detailed numerical simulations, we show that genuine multipartite entangled states can be faithfully prepared within current experimental platforms and discuss the role of the main decoherence sources, qubit dephasing and relaxation, depending on the network topology.
Quantum entanglement plays a central role in many quantum communication protocols. It allows distant particles to share correlations beyond the limits of classical interactions. Entanglement is essential for superdense coding, quantum teleportation, and secure cryptographic key distribution in quantum communication. It is also a pillar for developing quantum networks, where the management and distribution of entanglement are crucial for connecting distant nodes. Although perfect entanglement is a sought-after ideal, experimental imperatives, including entanglement distribution over long distances, often limit the quality of entangled states. An important question is whether weaker entanglement still offers advantages. First, we study more general tasks than dense coding to show that simpler measurements, combined with entanglement, allow advantageous and sometimes even optimal qubit communication protocols to be obtained. We also demonstrate that simple measurements can generate quantum correlations that cannot be modelled by two classical communication bits and can constitute an optimal protocol with quantum resources. We implement a novel Bell-type inequality tailored for certifying full network non-locality (FNN) to develop certification methods guaranteeing security on an entanglement-based network. Our experiment uses two pairs of polarised entangled photons in a network configuration with three nodes, briefly referred to as a bilocal network scenario. Finally, we show that weakly entangled states can improve communication over a qubit channel using only separate (local) measurements on isotropic non-steerable two-qubit states, without interference, of individual photons, across two communication tasks: secret sharing and its stochastic variant.
Scaling the number of entangled nodes in a quantum network is a challenge with significant implications for quantum computing, clock synchronisation, secure communications, and quantum sensing. In a quantum network, photons interact with matter qubits at different nodes, flexibly enabling the creation of remote entanglement between them. Multipartite entanglement among multiple nodes will be crucial for many proposed quantum network applications, including quantum computational tasks and quantum metrology. To date, experimental efforts have primarily focused on generating bipartite entanglement between nodes, which is widely regarded as the fundamental quantum resource for quantum networks. However, relying exclusively on bipartite entanglement to form more complex multipartite entanglement introduces several challenges. These include the need for ancillary qubits, extensive local entangling operations which increases the preparation latency, and increasingly stringent requirements on coherence times as the number of nodes grows. Here, we analyse various schemes that achieve multipartite entanglement between nodes in a single step, bypassing the need for multiple rounds of bipartite entanglement. We demonstrate that different schemes can produce distinct multipartite entangled states, with varying fidelity and generation rates. Additionally, we discuss the applicability of these schemes across different experimental platforms, highlighting their primary advantages and disadvantages.
Quantum-energy teleportation (QET) has so far only been realised on a two-qubit platform. Real-world communication, however, typically involves multiple parties. Here we design and experimentally demonstrate the first multi-qubit QET protocol using a robust W-state multipartite entanglement. Three-, four- and five-qubit circuits were executed both on noiseless simulators and on IBM superconducting hardware. In every case a single sender injects an energy E0 that is then deterministically and decrementally harvested by several remote receivers, confirming that energy introduced at one node can be redistributed among many entangled subsystems at light-speed-limited classical latency. Our results open a practical route toward energy-aware quantum networks.