QuantumAtlas

Cryptography & Communication

Quantum Internet

A proposed network that distributes entanglement between distant quantum devices, enabling quantum communication, sensing, and distributed computing.

Definition

A quantum internet would connect quantum computers, sensors, and clocks so that they can share entanglement and send quantum states, not just ordinary bits. Today's internet moves classical data and cannot do this. The quantum version would not replace the classical internet but run alongside it, adding abilities such as unconditionally secure communication, linking many small quantum computers into a larger one, and combining distant sensors into one more precise instrument.

In depth

The central difficulty is that quantum states cannot be copied or amplified. A photon carrying a qubit through fiber is lost with a probability that grows exponentially with distance, and there is no way to boost its signal as in a classical network. The solution is quantum repeaters: devices that create entanglement over short links, store it in quantum memories, and connect the links using entanglement swapping. Building memories with long coherence times and efficient light-matter interfaces is the main hardware challenge.

Prototypes demonstrate the pieces. Researchers at QuTech in Delft linked three nitrogen-vacancy nodes in 2021 with entanglement and a quantum network protocol, and a Harvard and AWS team in 2024 distributed entanglement between silicon-vacancy memories across about 35 kilometers of fiber in the Boston area. Chinese groups created a space-ground network, using the Micius satellite, extending over about 4,600 kilometers, and EPB in Chattanooga operates a commercial quantum network with IonQ technology. The Quantum Internet Alliance in Europe coordinates a roadmap to a prototype network.

Potential applications fall into three families. Secure communication includes quantum key distribution and device-independent protocols. Distributed quantum computing connects separate processors, which could scale beyond what one chip or cryostat can hold, and blind quantum computing lets a client run a computation on a remote server without revealing it. Networked sensing could combine telescopes and clocks into larger, more accurate instruments.

Technical Definition

A quantum network consists of nodes with quantum memories and processors connected by quantum channels, typically optical fibers or free space, plus a classical network for control. Entanglement is distributed between neighbors and extended by quantum repeaters using entanglement swapping and purification. Wehner, Elkouss, and Hanson described six stages of development, from trusted-repeater networks to networks of fault-tolerant quantum computers.

Visual Explanation: An Analogy

The classical internet sends letters that can be copied and forwarded. A quantum internet is more like a system that links pairs of special coins that always match in a mysterious way, and uses that link to do things that letters cannot, such as proving no one has read a message.

Key facts

ItemDetail
Key problemEntanglement cannot be amplified, so repeaters are needed beyond a few hundred kilometers
Six stagesDescribed by Wehner, Elkouss, and Hanson in 2018, from trusted repeaters to quantum computing networks
PrototypesDelft three-node network (2021), Harvard and AWS 35 km Boston link (2024), EPB Chattanooga
Space-ground linkMicius-based network spanning about 4,600 km (2021)
TimelineRegional networks in the 2030s; global scale is a longer-term goal

Where the idea comes from

The idea grew from the work on teleportation and quantum repeaters in the late 1990s, with H. Jeff Kimble's 2008 vision paper The Quantum Internet drawing wide attention. The first multi-node entanglement networks were demonstrated in the 2020s.

Real-World Use Cases

  • Distributing entanglement for key distribution and secure communication.
  • Connecting small quantum processors into larger distributed machines.
  • Networking sensors and clocks for improved precision.
  • Blind quantum computing, where clients keep their data private from servers.

How it differs from related ideas

  • The classical internet copies and amplifies signals, while a quantum internet cannot copy states and needs repeaters.
  • A QKD network distributes keys, while a quantum internet distributes entanglement for many applications.
  • It will run alongside the classical internet, which carries the control and classical communication.

Common Misconceptions

  • A quantum internet is not faster than the classical internet. It offers different capabilities.
  • It does not allow faster-than-light messaging.
  • It is not built yet beyond prototypes.

Frequently asked questions

What is the quantum internet?

A network that distributes entanglement and quantum states between distant quantum devices, working alongside the classical internet.

Does it exist today?

Only as small prototypes and research networks, such as those in Delft, Boston, and Chattanooga.

Why are repeaters needed?

Because quantum signals cannot be amplified or copied, repeaters extend entanglement over long distances.

Related Terms

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