The quantum internet represents the next frontier in secure communications — a global network that uses the strange properties of quantum mechanics to transmit information in ways that are fundamentally impossible to intercept or hack. While the classical internet transformed how we share information, the quantum internet promises to transform how we protect it.
Quantum Mechanics and Communication
The quantum internet relies on two key phenomena from quantum physics: superposition and entanglement. Superposition allows quantum bits (qubits) to exist in multiple states simultaneously, unlike classical bits that are either 0 or 1. Entanglement creates a mysterious connection between two particles — measuring one instantly determines the state of the other, regardless of the distance separating them. Einstein famously called this “spooky action at a distance.”
These properties enable quantum key distribution (QKD), the most mature application of quantum networking. In QKD, two parties share encryption keys encoded in the quantum states of photons. Any attempt to intercept these photons inevitably disturbs their quantum states, immediately alerting both parties to the eavesdropping attempt. This security guarantee is based on the laws of physics rather than mathematical complexity, making it immune to advances in computing power — including future quantum computers that could break today’s encryption.
Building Blocks of the Quantum Internet
Constructing a quantum internet requires several key technologies. Quantum repeaters are essential for extending the range of quantum communication beyond a few hundred kilometres — the current limit for transmitting single photons through optical fibres before they are absorbed. Unlike classical repeaters that simply amplify signals, quantum repeaters must preserve delicate quantum states, requiring sophisticated techniques such as entanglement swapping and quantum error correction.
Quantum memories store quantum information for the brief periods needed to synchronise network operations. These devices must maintain quantum coherence — the fragile quantum properties of stored information — for long enough to be practical. Research groups have achieved storage times ranging from milliseconds to hours using various approaches, including trapped atoms, nitrogen-vacancy centres in diamond, and rare-earth-doped crystals.
Current Progress
China has taken an early lead in quantum networking. The Micius satellite, launched in 2016, demonstrated intercontinental quantum key distribution between Beijing and Vienna. China has also built a 2,000-kilometre ground-based quantum communication backbone connecting Beijing to Shanghai, used by banks and government agencies for secure communications.
In Europe, the European Quantum Communication Infrastructure (EuroQCI) initiative aims to build a continent-wide quantum communication network. The Netherlands has pioneered quantum network testbeds, with researchers at Delft University successfully connecting three quantum processors in a rudimentary quantum network — the first multi-node quantum network in the world.
In North America, research groups are developing quantum network testbeds in Chicago, New York, and other cities, often running quantum signals alongside classical internet traffic through existing fibre-optic infrastructure.
Beyond Secure Communication
The quantum internet will enable applications far beyond encryption. Distributed quantum computing would allow multiple quantum processors to work together on problems too large for any single machine. Quantum sensor networks could achieve unprecedented precision in fields ranging from geological surveying to medical imaging. Blind quantum computing would let users run computations on remote quantum computers without revealing their data or algorithms to the computer’s operator.
While a fully functional global quantum internet remains years or decades away, the foundational technologies are advancing rapidly. The transition from laboratory demonstrations to practical infrastructure is underway, and the quantum internet may ultimately prove as transformative as the classical internet that preceded it.
