TOPOS · Long-form guide
Quantum Internet: how teleportation becomes a network
The quantum internet is not a faster internet. It is a different network, built on entanglement instead of copied packets, whose elementary operation is quantum teleportation of a state |ψ⟩ from one node to another.
What the quantum internet actually is
A quantum internet is a mesh of nodes — quantum computers, sensors, or key devices — connected by channels that distribute entangled pairs. Once two nodes share entanglement, either side can teleport an unknown quantum state to the other using a local Bell measurement and two classical bits sent over an ordinary link.
Because the no-cloning theorem forbids copying an unknown state, the network cannot store-and-forward like the classical internet. The primitive is entanglement distribution, not packet routing.
The three building blocks
- Entanglement sources — photon pairs produced by spontaneous parametric down-conversion or by atomic and solid-state emitters (NV centres, trapped ions, quantum dots).
- Quantum channels — telecom fibre for metropolitan links and free-space or satellite links (Micius, 2017) for intercontinental hops. Loss is exponential in distance, which is why repeaters matter.
- Quantum repeaters — nodes with quantum memory and entanglement swapping that extend a link without ever measuring the payload. Without them a fibre network tops out around a few hundred kilometres.
Why it is unhackable in principle
Quantum key distribution (BB84, E91) lets two nodes agree on a secret key whose security is guaranteed by measurement disturbance: any eavesdropper leaves detectable noise on the channel. This is a physical law, not a computational assumption, so a future quantum computer cannot retroactively break traffic recorded today — the harvest-now-decrypt-later attack that threatens RSA and ECC.
Instantaneous state transfer, not FTL messaging
The correlations between entangled particles are instantaneous, but their outcomes are random. To turn correlations into a usable state at the destination, the sender must transmit two classical bits telling the receiver which unitary to apply. Those bits travel at or below the speed of light, so no information moves faster than c. What is new is what moves: a full quantum state, not just a bitstring.
Where we are (2017–2026)
- 2017 — Micius satellite: entanglement distribution over 1,200 km and ground-to-satellite teleportation over 1,400 km.
- 2020 — Beijing–Shanghai QKD backbone (~2,000 km with trusted nodes).
- 2022 — Delft demonstrates a three-node entanglement-swapping network with memory.
- 2023–2024 — Boston, New York, Munich and Paderborn deploy metropolitan quantum links over deployed fibre.
- 2024–2026 — Quantinuum, IBM Quantum and academic groups run networked logical qubits with error-corrected teleportation gates.
What still has to happen
- Long-lived quantum memories in telecom-compatible wavelengths.
- High-rate, deterministic entanglement sources.
- Repeaters that beat the PLOB rate-loss bound over continental spans.
- Standardised stacks — a "quantum TCP/IP" — so heterogeneous nodes can interoperate.
Why it matters
The classical internet moves copies of information. The quantum internet moves the information itself — and only once. That is the exact operation that lets distributed quantum computers behave like a single machine, clock networks reach the fundamental limit of precision, and cryptographic keys become tamper-evident by construction.
FAQ
Is the quantum internet a faster internet?
No — it is a different network for quantum states, not a speed upgrade for web traffic.
Can it transmit data faster than light?
No. Teleportation always needs a classical side channel that respects the speed of light.
Why can't it just copy quantum data like the classical internet?
The no-cloning theorem forbids copying unknown quantum states; the network distributes entanglement instead.
Is it real yet?
Metropolitan links and satellite QKD are operational. A continental repeater backbone is still under construction.