Large-scale quantum networks do not exist yet, but some components of what would make up such networks are being studied. However, the control mechanism for such a large-scale network has not been developed. An article in AVS Quantum Science outlines how a time-sensitive network control plane could be a key component of a workable quantum network.
Quantum networks move quantum bits of information, called qubits, through the network to enable communication between devices and over distances. These qubits are usually photons. Through the quantum phenomena of superposition and entanglement, they can transmit much more information than classical bits, which are limited to logical states of 0 and 1, are able to. Successful long-distance transmission of a qubit requires precise control and timing.
In addition to the well-understood requirements of transmission distance and data rate, for quantum networks to be useful in a real-world setting there are at least two other requirements of industry that need to be considered.
One is real-time network control, specifically time-sensitive networking. This control method, which takes network traffic into account, has been used successfully in other types of networks, such as Ethernet, to ensure messages are transmitted and received at precise times. This is precisely what is required to control quantum networks.
The second requirement is cost. Large-scale adoption of an industrial quantum network will only happen if costs can be significantly reduced. One way to accomplish cost reduction is with photonic integrated circuits.
"The value of quantum technologies in industry must be favorable before it will be adopted," said author Stephen Bush. "In particular, a 'quantum advantage' must exist in which a quantum technology has the ability to outperform a classical technology (computing, communication, or sensing)."