Quantum Network Architectures

By leveraging the unique properties of quantum entanglement, Quantum Networks (QN) empower the design of innovative teleportation-based networked applications that cannot be achieved through classical networks (CNs). Such applications will require the deployment of extended quantum networks, delivering entanglement on-demand to quantum processing nodes. It has long been understood that Quantum Repeaters (QR) will be the backbone of such an extended network. We investigate the implementation of a working QR by using a new architectural model, the quantum internet stack. In a stack-driven QR setup, a quantum physical layer comprising entanglement sources (ESs) and quantum memories (QMs) will facilitate the transmission of non-classical correlations. These photons will be directed towards entanglement-swapping nodes, where high-quality entanglement can be extracted and efficiently distributed across extensive distances. Once entanglement is distributed, a quantum teleportation layer is used to provide on-demand teleportation services among the quantum processing nodes. 

The abstract quantum internet stack (orange) required for robust entanglement distribution. This abstraction translates into specific functionalities at the network level: Quantum devices, entanglement delivery, and quantum repeater functionality (dark blue). The two upper functionality layers (light orange, light blue) use teleportation services.

Stack-driven QRs will require on-demand fundamental QN operations, such as entanglement generation, routing, quantum storage, memory status verification, and entanglement swapping  measurements. These fundamental operations will also require precise time synchronization, fast remote control, and coordination over ancillary classical network infrastructure. This will form a core set of quantum communication primitives necessary for utilizing the network. Additionally, we envisage the need to enable entanglement-based applications to access the quantum repeater functionalities via well-defined application programming interfaces (APIs), a motivation to implement the quantum internet stack using Software-Defined Networking (SDN) principles. 

Building on years of experience developing quantum memories and entanglement sources, we emphasize on making them compatible with real-time network control using the principles of SDN (Building Block I). The development of QR hardware is also informed by the design of quantum-aware fast classical control networks capable of governing entanglement swapping procedures across long-distance optical links (Building Block II). The interconnection and coexistence of hybrid quantum/classical networks, providing the functionality of a QR, are also simultaneously informed by detailed network simulations, including the use of time-dependent dynamics of quantum devices, the stochasticity of photon delivery over fiber networks, and the quantum optical effects associated with quantum interference in a long-distance network (Building Block III).

Building blocks of a stack-driven quantum repeater: (I) configurable quantum communication hardware, (II) robust quantum-aware network control and (III) experimentally-inspired quantum network simulation. The development of quantum communication technology will be directly influenced by the cross-fertilization of ideas simultaneously conceived in the development of quantum-aware classically-controlled networks and the results obtained from the experimentally inspired quantum network simulations. These simulations will be directly influenced by the design constraints of the classical control networks, including time synchronization and software-defined control approaches.