Quantum networks have the potential to enhance the utility of quantum protocols (for, e.g., cryptography, communication, computation, etc.) by enabling the interoperation of multiple quantum systems. In this paper, we address the distribution of entanglement to the neighbors of a central entanglement source node equipped with a number of sources of entangled photon pairs. A switching network can be an effective component connecting the central node to its neighbors, thus enabling the reconfigurable routing of generated photons. We consider optimal (in terms of insertion loss and the number of component switches) photonic switching networks designed to satisfy the particular requirements of entanglement distribution. We begin by developing a rigorous framework for the study of such entanglement-distribution switching networks. Next, we devise and apply search strategies to design optimal switching networks applicable to entanglement source nodes with 10 or fewer neighbors. Scalable switching networks are then considered for an arbitrarily large number of neighbors, resulting in asymptotically optimal switching fabrics. For all designs, we address efficient routing algorithms for determining a switching-network state that provides the entanglement distribution desired of the switching network at a given time. The combination of optimal switching-network structures and associated efficient routing algorithms addresses a key component of entanglement distribution, thus advancing the state of the art of quantum networks toward practical implementation.
Quantum networks have the potential to enhance the utility of quantum protocols (for, e.g., cryptography, communication, computation, etc.) by enabling the interoperation of multiple quantum systems. In this paper, we address the distribution of entanglement to the neighbors of a central entanglement source node equipped with a number of sources of entangled photon pairs. A switching network can be an effective component connecting the central node to its neighbors, thus enabling the reconfigurable routing of generated photons. We consider optimal (in terms of insertion loss and the number of component switches) photonic switching networks designed to satisfy the particular requirements of entanglement distribution. We begin by developing a rigorous framework for the study of such entanglement-distribution switching networks. Next, we devise and apply search strategies to design optimal switching networks applicable to entanglement source nodes with 10 or fewer neighbors. Scalable switching networks are then considered for an arbitrarily large number of neighbors, resulting in asymptotically optimal switching fabrics. For all designs, we address efficient routing algorithms for determining a switching-network state that provides the entanglement distribution desired of the switching network at a given time. The combination of optimal switching-network structures and associated efficient routing algorithms addresses a key component of entanglement distribution, thus advancing the state of the art of quantum networks toward practical implementation.
The distribution of quantum entanglement appears to be an important component of applications of quantum communications and networks. The ability to centralize the sourcing of entanglement in a quantum network can provide for improved efficiency and enable a variety of network structures. A necessary feature of an entanglement-sourcing network node comprising several sources of entangled photons is the ability to reconfigurably route the generated pairs of photons to network neighbors depending on the desired entanglement sharing of the network users at a given time. One approach to such routing is the use of a photonic switching network. The requirements for an entanglement distribution switching network are less restrictive than for typical conventional applications, leading to design freedom that can be leveraged to optimize additional criteria. In this paper, we present a mathematical framework defining the requirements of an entanglement-distribution switching network. We then consider the design of such a switching network using a number of 2 × 2 crossbar switches, addressing the interconnection of these switches and efficient routing algorithms. In particular, we define a worst-case loss metric and consider 6 × 6, 8 × 8, and 10 × 10 network designs that optimize both this metric and the number of crossbar switches composing the network. We pay particular attention to the 10 × 10 network, detailing novel results proving the optimality of the proposed design. These optimized network designs have great potential for use in practical quantum networks, thus advancing the concept of quantum networks toward reality.
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.
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.
Entanglement routing plays a vital role in distributed quantum computing and quantum networks. Previous works on entanglement routing have addressed several design challenges due to limited quantum resources, failures to establish entanglement, and decoherence of established entanglement, but considered neither the limitations imposed by having a limited number of entangled photon sources (EPSes), nor the benefits of using all-optical (or quantum) switching to distribute entangled photons. In this paper, we first explore the problem of jointly optimizing entanglement routing and EPS assignment, assuming no all-optical switching capability. In other words, a pair of entangled photons generated by one EPS can be distributed to two neighboring quantum nodes. We then relax the above assumption so as to allow a pair of entangled photons generated by one EPS to be distributed to non-adjacent nodes using all-optical switching. We propose two corresponding solutions, namely, entanglement routing and EPS assignment (or ERSA), and ERSA with all-optical switching-based distribution (or ERSA+D) that aim to maximize the number of entanglement connections between the given set of source-destination (SD) pairs while avoiding starvation and achieving fairness among the SD pairs. In order to obtain efficient solutions in a large discrete solution space in a timely manner, we first formulate each optimization problem as an Integer Linear Programming (ILP), and then propose efficient algorithms to derive near-optimal solutions based on relaxation, Lagrangian decomposition, duality iteration, and rounding techniques. Extensive simulations show that ERSA+D can increase network throughput by up to 1652% and 113%, respectively, thanks to EPS assignment optimization, and all-optical switching based entanglement distribution.
Entanglement distribution networks are essential for enabling secure, reliable, and sustained communication through the future Quantum Internet. Multi-ring network topologies offer improved scalability and redundancy, but also introduce additional routing complexity for the task of efficiently distributing entanglement. This paper solves the problem of optimal entanglement distribution in multi-ring quantum network topologies. Two separate multi-ring network configurations are analyzed, one where requests can only be routed within a single ring layer, and involves a less complex node setup, and one where requests may switch ring layers when passing through the network's nodes, at the cost of additional complexity within the nodes themselves. We propose algorithms that solve the problem of entanglement distribution in terms of optimal time needed to satisfy a set of entanglement resupply requests with given network resources, as well as the problem of optimal resources in order to satisfy a set of entanglement resupply requests within a single entanglement transmission and measurement step. We provide a comprehensive analysis of the proposed algorithms through computer simulations, which indicate that the additional complexity of a network which allows switching between ring layers brings little benefit in terms of time to serve requests, but may reduce the number of resources needed to satisfy the entanglement distribution requests in a non-blocking manner.
Large-scale quantum networks with thousands of nodes require scalable network protocols and physical hardware to realize. In this work, we introduce packet switching as a new paradigm for quantum data transmission in both future and near-term quantum networks. We propose a classical-quantum data frame structure and explore methods of frame generation and processing. Further, we present conceptual designs for a quantum reconfigurable optical add-drop multiplexer to realize the proposed transmission scheme. Packet switching allows for a universal design for a next generation Internet where classical and quantum data share the same network protocols and infrastructure. In this new quantum networking paradigm, entanglement distribution, as with quantum key distribution, is an application built on top of the quantum network rather than as a network designed especially for those purposes. For analysis of the network model, we simulate the feasibility of quantum packet switching for some preliminary models of quantum key and entanglement distribution. Finally, we discuss how our model can be integrated with other network models toward a realization of a quantum Internet.