Top 20 Quantum Internet Terms You Need to Know
The essential vocabulary for the coming quantum network revolution
The quantum internet promises to connect quantum devices across cities, continents, and eventually the globe, enabling unhackable communications, distributed quantum computing, and entirely new classes of networked applications. While much of the underlying technology is still in development, the vocabulary is taking shape now. These 20 terms form the foundation you need to understand how quantum networks work, why they matter, and where the field is heading.
Quantum Internet
The quantum internet is a proposed global network that connects quantum processors, sensors, and communication devices using quantum signals. Unlike the classical internet, which transmits bits, the quantum internet would distribute entanglement and quantum states between nodes, enabling fundamentally new capabilities such as provably secure communication, distributed quantum computation, and coordinated quantum sensing. Several national and international programmes are actively building testbed quantum networks as stepping stones toward this goal.
Quantum Key Distribution (QKD)
Quantum key distribution is a method for two parties to generate a shared secret cryptographic key with security guaranteed by the laws of quantum mechanics. Any attempt to eavesdrop on the quantum channel introduces detectable disturbances. Leading protocols include BB84, which uses the polarisation states of single photons, and E91, which relies on entangled photon pairs. QKD is the most commercially mature quantum networking application, with deployed fibre and satellite-based systems already in operation.
Entanglement Distribution
Entanglement distribution is the process of creating and sharing entangled quantum states between two or more distant nodes in a quantum network. It is the foundational resource of the quantum internet, as nearly all quantum networking protocols depend on shared entanglement. Entanglement can be distributed through optical fibres or free-space links, but photon loss over distance remains a major challenge, driving the need for quantum repeaters.
Quantum Repeater
A quantum repeater is a device designed to extend the range of quantum communication beyond the limits imposed by photon loss in optical fibres. Unlike classical repeaters, which amplify signals, quantum repeaters use entanglement swapping and quantum error correction to relay quantum states without measuring and collapsing them. Developing practical, deployable quantum repeaters is one of the most critical engineering challenges on the path to a long-distance quantum internet.
Quantum Teleportation
Quantum teleportation is a protocol that transfers an unknown quantum state from one location to another using shared entanglement and classical communication. The original state is destroyed at the sender and reconstructed at the receiver, without the quantum information physically traversing the intervening space. Quantum teleportation is a core primitive of the quantum internet, underpinning applications from distributed quantum computing to entanglement-based networking protocols.
Entanglement Swapping
Entanglement swapping is a technique that creates entanglement between two particles that have never directly interacted, by performing a joint measurement on two intermediary particles that are each entangled with one of the target particles. It is the key mechanism inside quantum repeaters, allowing entanglement to be extended across multiple network segments without requiring a direct quantum channel between the endpoints.
Quantum Memory
A quantum memory is a device that can store a quantum state and retrieve it on demand at a later time. Quantum memories are essential for quantum repeaters and for synchronising operations across a quantum network, since photons arrive at unpredictable times and entanglement must be held until both ends are ready. Candidate platforms include atomic ensembles, rare-earth-doped crystals, nitrogen-vacancy centres in diamond, and trapped ions.
Quantum Channel
A quantum channel is any physical medium used to transmit quantum information from one location to another. The most common quantum channels are optical fibres and free-space links (including satellite-to-ground paths). Quantum channels are inherently lossy and noisy, which limits the distance over which quantum states can be reliably transmitted and drives the need for quantum repeaters and error correction in networking applications.
Quantum Node
A quantum node is an endpoint in a quantum network capable of generating, processing, storing, and measuring quantum states. A fully functional quantum node typically combines a quantum processor with quantum memory and an interface to quantum communication channels. The capabilities of individual nodes determine which quantum networking applications can be supported, from basic QKD to full distributed quantum computation.
BB84 Protocol
BB84 is the first and most widely implemented quantum key distribution protocol, proposed by Charles Bennett and Gilles Brassard in 1984. It uses single photons prepared in one of two conjugate bases to encode key bits. After transmission, the sender and receiver publicly compare their basis choices and discard mismatched measurements, then perform classical post-processing to detect eavesdropping and distil a secure key.
E91 Protocol
The E91 protocol is a quantum key distribution scheme proposed by Artur Ekert in 1991 that uses entangled photon pairs shared between two parties. Its security is rooted in the violation of Bell inequalities, which guarantees that the correlations between measurement results cannot be replicated by any classical eavesdropper. E91 offers a conceptual advantage over BB84 in that its security proof is device-independent, tied directly to the fundamental non-locality of quantum mechanics.
Bell State
A Bell state is one of four maximally entangled two-qubit quantum states. Named after physicist John Bell, these states form the standard basis for entanglement-based protocols in quantum networking. Bell states are central to quantum teleportation, entanglement swapping, superdense coding, and QKD. Generating and distributing high-fidelity Bell states between distant nodes is one of the primary benchmarks for quantum network performance.
Bell State Measurement (BSM)
A Bell state measurement is a joint measurement on two qubits that projects them into one of the four Bell states. BSMs are the critical operation at the heart of quantum teleportation and entanglement swapping. Performing a complete BSM with linear optics alone is fundamentally limited to 50% success probability, which is one reason why photonic quantum networking protocols often require multiple attempts or auxiliary resources to succeed deterministically.
Quantum Network Stack
The quantum network stack is a layered architecture that organises the protocols and services needed to operate a quantum internet, analogous to the OSI model for classical networking. Proposed layers include the physical layer (photon transmission), the link layer (entanglement generation between adjacent nodes), the network layer (entanglement routing across multiple hops), the transport layer (reliable end-to-end entanglement delivery), and the application layer (QKD, distributed computing, and other user-facing services).
Entanglement Purification (Distillation)
Entanglement purification, also called entanglement distillation, is a process that takes multiple copies of low-fidelity entangled pairs and produces fewer pairs of higher fidelity. It is essential for quantum networking because entanglement quality degrades as it passes through lossy and noisy channels. Purification protocols sacrifice quantity for quality, ensuring that the entanglement delivered to end users is good enough for the target application.
Satellite Quantum Communication
Satellite quantum communication uses orbiting spacecraft to distribute quantum signals over intercontinental distances, bypassing the exponential photon loss that limits fibre-based links beyond a few hundred kilometres. China’s Micius satellite demonstrated satellite-to-ground QKD and entanglement distribution over more than 1,200 kilometres in 2017. Several nations and commercial ventures are now pursuing satellite-based quantum networks as a route to global-scale quantum connectivity.
Trusted Node
A trusted node is an intermediate point in a quantum network where quantum keys are decrypted and re-encrypted classically, requiring the node itself to be physically secure. Trusted nodes are a practical workaround for extending QKD range before quantum repeaters are available, but they represent a security compromise because the key material is exposed in plaintext at each node. Most deployed QKD networks today, including the Beijing-Shanghai backbone, rely on trusted nodes.
Blind Quantum Computing
Blind quantum computing is a protocol that allows a client with minimal quantum capability to delegate a computation to a remote quantum server without the server learning anything about the input, the computation, or the output. It relies on the client sending specially prepared qubits over a quantum network. Blind quantum computing is a compelling application of the quantum internet, offering privacy guarantees that have no classical equivalent.
Distributed Quantum Computing
Distributed quantum computing connects multiple quantum processors via a quantum network so they can work together on computations too large for any single device. Entanglement shared between processors enables non-local quantum gates, effectively creating a virtual quantum computer whose qubit count exceeds that of any individual node. This approach is increasingly seen as a scalable path to large-scale quantum computing, complementing efforts to build ever-bigger monolithic processors.
Quantum Network Testbed
A quantum network testbed is an experimental quantum communication infrastructure built to develop, test, and benchmark quantum networking technologies under real-world conditions. Notable examples include the Chicago Quantum Exchange network, the European Quantum Communication Infrastructure (EuroQCI), the UK Quantum Network, and the Dutch QuTech quantum internet demonstrator in Delft. These testbeds serve as proving grounds for hardware, protocols, and applications before commercial-scale deployment.
