With the advent of the construction and deployment of entanglement-based quantum networks, the efficient use of network resources will become a critical challenge for the scalable operation of such a system. Recently, architectures that incorporate memoryless optical switches have gained attention for forwarding entangled photons. By leveraging these architectures, costly resources such as high efficiency Bell State Analyzers (BSAs) can be shared across the network. Nevertheless, the introduction of switching substantially complicates the process of multiplexing and resource allocation compared to an individual link. In this work, we propose a switching protocol for unbuffered, multidrop quantum networks in a photonic synchronization domain that establishes a link between two end nodes using a shared BSA in the switched network. To achieve this, two end nodes cooperatively select the target BSA node with the lowest path cost and independently reserve each path within the network. Bi-path reservations are performed to allocate resources in a distributed manner. The proposed protocol is evaluated through simulation on Q-Fly network topologies under varying traffic conditions. The results demonstrate high link establishment success with stable performance even under increased network load. These capabilities which are driven by our proposed protocol are an essential way to realize large-scale, managed, and automated quantum networks.
With the advent of the construction and deployment of entanglement-based quantum networks, the efficient use of network resources will become a critical challenge for the scalable operation of such a system. Recently, architectures that incorporate memoryless optical switches have gained attention for forwarding entangled photons. By leveraging these architectures, costly resources such as high efficiency Bell State Analyzers (BSAs) can be shared across the network. Nevertheless, the introduction of switching substantially complicates the process of multiplexing and resource allocation compared to an individual link. In this work, we propose a switching protocol for unbuffered, multidrop quantum networks in a photonic synchronization domain that establishes a link between two end nodes using a shared BSA in the switched network. To achieve this, two end nodes cooperatively select the target BSA node with the lowest path cost and independently reserve each path within the network. Bi-path reservations are performed to allocate resources in a distributed manner. The proposed protocol is evaluated through simulation on Q-Fly network topologies under varying traffic conditions. The results demonstrate high link establishment success with stable performance even under increased network load. These capabilities which are driven by our proposed protocol are an essential way to realize large-scale, managed, and automated quantum networks.
Entanglement-based networks (EBNs) enable general-purpose quantum communication by combining entanglement and its swapping in a sequence that addresses the challenges of achieving long-distance communication with high fidelity associated with quantum technologies. In this context, entanglement distribution refers to the process by which two nodes in a quantum network share an entangled state, serving as a fundamental resource for communication. In this paper, we study the performance of entanglement distribution mechanisms over a physical topology comprising end nodes and quantum switches, which are crucial for constructing large-scale links. To this end, we implemented a switch-based topology in NetSquid and conducted a series of simulation experiments to gain insight into practical and realistic quantum network engineering challenges. These challenges include, on the one hand, aspects related to quantum technology, such as memory technology, gate durations, and noise; and, on the other hand, factors associated with the distribution process, such as the number of switches, distances, purification, and error correction. All these factors significantly impact the end-to-end fidelity across a path, which supports communication between two quantum nodes. We use these experiments to derive some guidelines towards the design and configuration of future EBNs.
There are two conventional methods to establish an entanglement connection in a Quantum Data Networks (QDN). One is to create single-hop entanglement links first and then connect them with quantum swapping, and the other is forwarding one of the entangled photons from one end to the other via all-optical switching at intermediate nodes to directly establish an entanglement connection. The two methods both have pros and cons. Respectively, the former method has a higher success probability of constructing entanglement link, but it would consume more quantum resources. The latter method, however, has a lower success probability to deliver a photon across multiple quantum links with fewer quantum resources. Accordingly, we are expecting to establish significantly more entanglement connections with limited quantum resources by first creating entanglement segments, each spanning multiple quantum link, using all-optical switching, and then connecting them with quantum swapping. In this paper, we design SEE, a Segmented Entanglement Establishment approach that seamlessly integrates quantum swapping and all-optical switching to maximize quantum network throughput. SEE first creates entanglement segments over one or multiple quantum links with all-optical switching, and then connect them with quantum swapping. Accordingly, SEE can theoretically outperform conventional entanglement link-based approaches. Large scale simulations show that SEE can achieve up to 100.00% larger throughput compared with the state-of-the-art entanglement link-based approaches, e.g., Redundant Entanglement Provisioning and Selection (REPS).
Abstract Distributing quantum states and entanglement between multiple pairs of nodes is a fundamental task in quantum communication and distributed quantum computing on large-scale quantum networks. In particular, the simultaneous distribution of quantum states or entanglement among multiple source-destination pairs (quantum k -pair communication task) is an emerging demand for scalable quantum networks. Here, we propose a quantum network architecture based on the Beneš switching topology that provides a universal switching framework for such pairwise communications. Our network architecture requires only O ( k log k ) pre-established entangled resources to accomplish the k -pair communication task, and offers advantages of non-blocking and low latency. We develop routing protocols for concurrent entanglement distribution and analyze their performance under ideal operating assumptions, while also discussing the effects of nonideal entanglement generation, quantum memory decoherence, photon loss, and finite Bell state measurement (BSM) success probability. The proposed framework requires local BSMs and entanglement swapping operations and is compatible in principle with quantum platforms supporting these capabilities. In particular, photonic implementations can benefit from mature photonic components and be compatible with existing telecommunications infrastructure.
The optical Bell State Analyzer (BSA) plays a key role in the optical generation of entanglement in quantum networks. The optical BSA is effective in controlling the timing of arriving photons to achieve interference. It is unclear whether timing synchronization is possible even in multi-hop and complex large-scale networks, and if so, how efficient it is. We investigate the scalability of BSA synchronization mechanisms over multiple hops for quantum networks both with and without memory in each node. We first focus on the exchange of entanglement between two network nodes via a BSA, especially effective methods of optical path coordination in achieving the simultaneous arrival of photons at the BSA. In optical memoryless quantum networks, including repeater graph state networks, we see that the quantum optical path coordination works well, though some possible timing coordination mechanisms have effects that cascade to adjacent links and beyond, some of which was not going to work well of timing coordination. We also discuss the effect of quantum memory, given that end-to-end extension of entangled states through multi-node entanglement exchange is essential for the practical application of quantum networks. Finally, cycles of all-optical links in the network topology are shown to may not be to synchronize, this property should be taken into account when considering synchronization in large networks.
To scale quantum computers to useful levels, we must build networks of quantum computational nodes that can share entanglement for use in distributed forms of quantum algorithms. In one proposed architecture, node-to-node entanglement is created when nodes emit photons entangled with stationary memories, with the photons routed through a switched interconnect to a shared pool of Bell state analyzers (BSAs). Designs that optimize switching circuits will reduce loss and crosstalk, raising entanglement rates and fidelity. We present optimal designs for switched interconnects constrained to planar layouts, appropriate for silicon waveguides and Mach-Zehnder interferometer (MZI)2×2switch points. The architectures for the optimal designs are scalable and algorithmically structured to pair any arbitrary inputs in a rearrangeable, non-blocking way. For pairingNinputs,N(N−2)/4switches are required, which is less than half of number of switches required for full permutation switching networks. An efficient routing algorithm is also presented for each architecture. These designs can also be employed in reverse for entanglement generation using a shared pool of entangled paired photon sources.
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.