The quantum internet is a proposed network infrastructure that connects quantum processors, sensors, and communication devices through quantum communication channels capable of transmitting qubits and distributing entanglement. Unlike the classical internet, which transmits bits, the quantum internet would transmit quantum states — enabling applications impossible with classical networking, including distributed quantum computing, blind quantum computing, and fundamentally secure communication.
The key technical challenge is distributing entanglement over long distances. Photons carrying quantum information are lost exponentially in optical fiber (approximately 0.2 dB/km at telecom wavelengths), limiting direct quantum communication to a few hundred kilometers. Quantum repeaters — devices that extend entanglement distances using entanglement swapping and quantum error correction — are the proposed solution, analogous to classical repeaters in telecommunications. However, practical quantum repeaters require quantum memories that can store quantum states for milliseconds while maintaining coherence, a capability still under active development.
Several countries have national quantum internet research programs. The US Department of Energy published a quantum internet blueprint in 2020. The EU's Quantum Internet Alliance is developing a multi-node quantum network across Europe. China has the most deployed quantum communication infrastructure, including the 2,000-km Beijing-Shanghai backbone. The Netherlands' QuTech has demonstrated a three-node quantum network with entanglement delivery on demand. Full-scale quantum internet deployment is expected to evolve through stages: trusted-node QKD networks (current), entanglement distribution networks (next 5-10 years), and fault-tolerant quantum networks (10-20+ years).