In the Quantum Internet, multipartite entanglement enables a rich and dynamic overlay topology, referred to as artificial topology, upon the physical one, that can be exploited for communication purposes. In fact, the ability to extractn-qubits GHZ states and EPR pairs from the original multipartite entangled state constitutes the resource primitives for end-to-end and on-demand quantum communications. Thus, in this paper, we theoretically determine upper and lower bounds for the number of extractablen-qubits GHZ states and EPR pairs involving nodes remote in the artificial topology, as well as the achievable sizenof remote GHZ states. The theoretical analysis is then complemented by the proposal of a novel algorithm, which provides in polynomial-time a heuristic solution to the above problem. This is remarkable, since the theoretical problem is NP-complete. The performance analysis demonstrates the proposed algorithm is able to effectively manipulate the original and arbitrary graph state for extracting entanglement resources across remote nodes.
In the Quantum Internet, multipartite entanglement enables a rich and dynamic overlay topology, referred to as artificial topology, upon the physical one, that can be exploited for communication purposes. In fact, the ability to extractn-qubits GHZ states and EPR pairs from the original multipartite entangled state constitutes the resource primitives for end-to-end and on-demand quantum communications. Thus, in this paper, we theoretically determine upper and lower bounds for the number of extractablen-qubits GHZ states and EPR pairs involving nodes remote in the artificial topology, as well as the achievable sizenof remote GHZ states. The theoretical analysis is then complemented by the proposal of a novel algorithm, which provides in polynomial-time a heuristic solution to the above problem. This is remarkable, since the theoretical problem is NP-complete. The performance analysis demonstrates the proposed algorithm is able to effectively manipulate the original and arbitrary graph state for extracting entanglement resources across remote nodes.
The extraction of EPR pairs andn-qubits GHZ states among remote nodes in quantum networks constitutes the resource primitives for end-to-end and on-demand communications. However, the Bell-VM problem, which determines whether a given graph state can be transformed into a set of Bell pairs on specific vertices (not necessarily remote), is known to be NP-complete. In this paper, we extend this problem, not only by focusing on nodes remote within generic graph states, but also by determining the number of extractablen-qubit remote GHZ states - beside the number of remote EPR pairs. The rationale for tackling the extraction of GHZ states among remote nodes, rather than solely remote EPR pairs, is that a GHZ state enables the dynamic extraction of an EPR pair between any pair of nodes sharing the state. This, in turn, implies the ability of accommodating the traffic requests on-the-fly. Specially, we propose a polynomial-time algorithm for solving the aforementioned NP-complete problem. Our results demonstrate that the proposed algorithm is able to effectively adapt to generic graph states for extracting entanglement resources across remote nodes.
In Quantum Local Area Networks (QLANs) - the near-term building block of the Quantum Internet - the choice of the physical network topology is not so restrictive and binding as in classical LAN in terms of communication capabilities among the network nodes. And the rationale for this is the entanglement-enabled connectivity induced by multipartite entangled states. Indeed, it is possible to create on-demand links between the QLAN nodes by properly manipulating the shared multipartite entangled states. Thus, it is possible to build an overlay entangled network upon the physical one, characterized by a topology different from the physical one and referred to as artificial topology. In this paper we address the fundamental issue of engineering the artificial topology to bypass the limitations induced by the physical network topology. This possibility to overcome the constraints in the network design induced by the physical topology has no counterpart in classical networks. To this aim, we exploit the properties of a class of multipartite entangled states, referred to as graph states, which exhibit unique properties, making them very interesting and promising for engineering artificial topologies in QLANs.
Multipartite entanglement plays a crucial role for the design of the Quantum Internet, due to its potentiality of significantly increasing the network performance. In this paper, we design an entanglement access control protocol for multipartite state, which exhibits several attractive features. Specifically, the designed protocol is able to jointly extract in a distributed way an EPR pair from the original multipartite entangled state shared by the set of network nodes, and to univocally determines the identities of the transmitter node and the receiver node in charge of using the extracted EPR pair. Furthermore, the protocol avoids to delegate the signaling arising with entanglement access control to the classical network, with the exception of the unavoidable classical communications needed for EPR extraction and qubit teleportation. Finally, the protocol supports the anonymity of the entanglement accessing nodes.
Entanglement is unanimously recognized as the key communication resource of the Quantum Internet. Thus, the possibility of implementing unparalleled network functionalities by exploiting entanglement is gaining huge attention. However, the research efforts in this context are mainly focused onbipartite entanglement, often discarding the wide unexplored classes of entanglement shared among more than two parties, known asmultipartite entanglement. In this paper, we aim at exploiting multipartite entanglement asinter-network resource. Specifically, we consider the interconnection of different Quantum Local Area Networks (QLANs), and we show that multipartite entanglement allows to dynamically generate an inter-QLANartificialtopology, by means of local operations only, that overcomes the limitations of the physical QLAN topologies. To this aim, we first design the multipartite entangled state to be distributed within each QLAN. Then, we show how such a state can be engineered to: i) interconnect nodes belonging to different QLANs, and ii) dynamically adapt to different inter-QLAN traffic demands. Our contribution aims at providing the network engineering community with a hands-on guideline towards the concept of artificial topology and artificial neighborhood.
Distributing quantum entanglements over long distances is essential for the realization of a global scale quantum Internet. Most of the prior work and proposals assume an on-demand distribution of entanglements which may result in significant network resource under-utilization. In this work, we introduce Quantum Overlay Networks (QONs) for efficient entanglement distribution in quantum networks. When the demand to create end-to-end user entanglements is low, QONs can generate and store maximally entangled Bell pairs (EPR pairs) at specific overlay storage nodes of the network. Later, during peak demands, requests can be served by performing entanglement swaps either over a direct path from the network or over a path using the storage nodes. We solve the link entanglement and storage resource allocation problem in such a QON using a centralized optimization framework. We evaluate the performance of our proposed QON architecture over a wide number of network topologies under various settings using extensive simulation experiments. Our results demonstrate that QONs fare well by a factor of 40% with respect to meeting surge and changing demands compared to traditional non-overlay proposals. QONs also show significant improvement in terms of average entanglement request service delay over non-overlay approaches.
The quantum internet will extend today's networks with a capability no classical infrastructure can offer: the distribution of entanglement between distant nodes. That single resource underlies services provably beyond classical reach, such as secure communication against computationally unbounded adversaries, blind delegated computation on remote quantum servers, and entangled networks of atomic clocks. Most of these services require a single multipartite state shared among several nodes at once — for the most part a graph state: one qubit per vertex of a graph, one entangling interaction per edge. This Thesis addresses the distribution of one such state: given an arbitrary network of entanglement switches, deliver the m-qubit path graph state, in the order the application requests, to m single-qubit end nodes — the weakest client model in the literature. Prior protocols support arbitrary topologies or such minimal end nodes, never both. The strongest of them are also centralized: the construction and the memory demand concentrate at a single node. The Thesis takes the opposite approach: a distributed protocol. The Path Graph State Distribution (PathGSD) protocol grows the target state one end node at a time behind a single reference qubit that walks a classically planned route, the shortest ordered Steiner walk. The work is partitioned among the switches, which coordinate only through entanglement and classical messages; no single node ever builds or stores the whole state. The design is deliberately simple, guided by engineering principles, and the simplicity pays at scale: planning is polynomial and completes in seconds on a network of 22,500 switches, where the closest optimization-based alternatives face exponential blow-up. Correctness is proved in the graph-state measurement calculus; a memory-reuse discipline and a parallel multi-domain execution mode complete the protocol. The protocol is implemented as communicating discrete-event processes on the QuantumSavory simulator, validated against exact theoretical expectations, and evaluated against the strongest available baselines: the star-specific Piecemaker and Factory protocols, simulated under noise, and the Graph State Transfer (GST) algorithm's proved cost expressions, evaluated exactly on arbitrary topologies. PathGSD consumes fewer Einstein-Podolsky-Rosen (EPR) pairs than the exact GST baseline on every single-domain family tested, keeps switch memory constant in the network size where the centralized baseline's grows, matches the star-specific protocols on their home topology, and reaches measured speed-ups of up to 1.9× when two administrative domains execute in parallel.