Quantum Networking Fundamentals: From Physical Protocols to Network Engineering

Abstract

The realization of the Quantum Internet promises transformative capabilities in secure communication, distributed quantum computing, and high-precision metrology. However, transitioning from laboratory experiments to a scalable, multi-tenant network utility introduces deep orchestration challenges. Current development is often siloed within physics communities, prioritizing hardware, while the classical networking community lacks architectural models to manage fragile quantum resources. This tutorial bridges this divide by providing a network-centric view of quantum networking. We dismantle idealized assumptions in current simulators to address the "simulation-reality gap," recasting them as explicit control-plane constraints. To bridge this gap, we establish Software-Defined Quantum Networking (SDQN) as a prerequisite for scale, prioritizing a symbiotic, dual-plane architecture where classical control dictates quantum data flow. Specifically, we synthesize reference models for SDQN and the Quantum Network Operating System (QNOS) for hardware abstraction, and adapt a Quantum Network Utility Maximization (Q-NUM) framework as a unifying mathematical lens for engineers to reason about trade-offs between entanglement routing, scheduling, and fidelity. Furthermore, we analyze Distributed Quantum AI (DQAI) over imperfect networks as a case study, illustrating how physical constraints such as probabilistic stragglers and decoherence dictate application-layer viability. Ultimately, this tutorial equips network engineers with the tools required to transition quantum networking from a bespoke physics experiment into a programmable, multi-tenant global infrastructure.

Figures (10)

• Figure 1: Single-photon qubit. An example of a single photon qubit. The qubit is encoded in the plane of oscillation of the electric field distinguishing horizontally and vertically polarized photons.
• Figure 2: Bloch sphere. A mathematical construction for representing single qubit transformation and states, where $\ket{\psi} = \cos{(\theta/2)}\ket{0} + e^{i\phi}\sin{(\theta/2)}\ket{1}$.
• Figure 3: Bell pair generation. Different representations for the generation of a $\ket{\Phi^{+}}$ state. At the circuit level, the state is generated by converting one of the qubits to a $\ket{+}$ superposition, followed by a $\mathrm{CNOT}$, which flips the target qubit in one branch of the superposition. This state can be prepared in different ways, and alternative diagrammatic notation may be used.
• Figure 4: Quantum state teleportation. A qubit can be reconstructed at distant location using a pre-shared Bell state and local Bell-state measurement (BSM). The BSM projects the unmeasured qubit into the original qubit's state up to two possible correction operations. The bits $a$ and $b$ are classical measurement results which determine whether or not correction operations must be applied.
• Figure 5: The entanglement swap circuit. The entanglement swap uses pre-shared entanglement and a local BSM to transfer the entanglement onto the unmeasured qubits. The procedure is identical to quantum state teleportation, but where the teleported qubit is already entangled with another qubit.