The Internet moves bits. Quantum networking teleports qubits. Teleporting quantum state between nodes.
A bit is the fundamental unit of classical information — a 0 or a 1, a switch that is off or on. The entire architecture of classical networking quietly depends on one property of bits: they can be copied freely. You send me a file, you still have the file. A switch or a router — the basic building blocks of the Internet — work on the same principle: store and forward. We have been doing this so long that it feels obvious.
A qubit — the quantum equivalent of a bit — is a stranger beast. It can exist in a superposition of 0 and 1 simultaneously, which is what gives quantum computation its power. The proverbial Schrödinger’s cat being dead and alive. But there is a catch. The no-cloning theorem, proven in 1982, says that any attempt to copy a qubit requires measuring it first, and measurement collapses the superposition.
Think of a qubit like a spinning coin; the moment you try to copy the information on it, you have to slap your hand down to see if it’s heads or tails. You can now make a copy, but the “spin” (superposition), is gone.
We’ve spent forty years perfecting a stack— HTTP, TCP/IP, Ethernet, the works — that treats data like an infinite supply of carbon copies. In the quantum world, that entire philosophy just jumped off of a cliff.
Entanglement
Quantum networking transfers quantum state through a completely different mechanism: entanglement and teleportation. Yes, teleportation. I know how that sounds. Hold your horses.
Entanglement is the property where two particles — usually photons — get linked in a way that measuring one tells you the state of the other, no matter how far apart they are. It’s two partners doing the tango in complete synchronicity, separated across any distance. Einstein hated this. He called it “spooky action at a distance,” and he meant it as an insult. It is also the foundational primitive of quantum networking.
Here is how you actually move a qubit from one quantum processor to another. You first distribute an entangled photon pair between them — one tango partner at each end. Then you perform a measurement on the sending side that, combined with a classical communication channel, lets the receiving side reconstruct the original quantum state. That is quantum teleportation. The state is reconstructed at the destination and destroyed at the source. No copy is made, ever.
This not something any of the classical networking protocols were designed to handle.
These implications impact every layer of the networking stack. A couple of examples below, though we will explore the full gamut of differences in future articles.
Switching: In the classical world, switching is like traffic control where the switch decides which highway a packet takes. But in a quantum network the resource is entanglement. You consume a pair of entangled photons that have to be generated and distributed before they lose their ‘quantumness’ (decoherence). All of this has to happen while preserving the quantum state of the photons themselves. Like a supply chain for milk where the product goes stale if you don’t use it within a small bounded window, and you cannot even open the carton to check, because opening it spoils what is inside.
Error correction: Classical networks detect errors and request retransmission. Quantum networks can’t retransmit, since, if you remember the spinning coin, measurement destroys state. Quantum error correction has to work by encoding logical qubits redundantly across multiple physical qubits and correcting errors without directly measuring the quantum information — network-wide.
The quantum datacenter architecture that emerges from these constraints looks nothing like its classical counterpart. Whereas a classical datacenter has compute, storage, and a network fabric, a quantum datacenter needs three distinct layers: (1) a physical layer of specialized quantum hardware, (2) an entanglement management layer that generates and distributes entangled pairs as a schedulable resource, and (3) an applications layer, inclusive of a network-aware compiler, that partitions quantum circuits across networked processors and coordinates their execution. The network between QPUs is distributing the entanglement that makes distributed quantum computing feasible.
The practical path forward, in addition to scaling up QPUs and quantum compute systems, is to connect many QPUs through this quantum network fabric. This combines the vertical scale-up within each QPU with the horizontal scale-out across the network. A design pattern that we have leveraged many times over — servers to cloud, VMs to microservices, databases to NoSQL and map-reduce. The critical difference is that the network primitive is now an entangled photon pair encoding qubits, and not a packet of bits.
This stack is being built right now. Follow along to go deeper on specific pieces of it.