The quantum internet is a proposed network that would allow quantum information to be shared between distant devices. Instead of relying only on the ordinary bits used by today’s internet, it would use quantum systems, such as individual photons or carefully controlled atoms, to transmit and store information according to the laws of quantum physics.
Its most important potential applications include highly secure communication, connections between quantum computers, and scientific experiments that require quantum systems to work together across long distances. Rather than replacing the existing internet, a quantum internet would most likely complement it, adding capabilities that conventional networks cannot provide.
The technology is based on real, experimentally demonstrated principles, including quantum entanglement and quantum teleportation. But building a reliable, large-scale network remains a substantial engineering challenge. Researchers must learn how to distribute quantum states over long distances, preserve them against environmental disturbances, and connect different devices without destroying the delicate information they carry.
Understanding how this network could work begins with a basic distinction: quantum information behaves differently from the digital information that moves through ordinary communication networks.
What makes the quantum internet different from today’s internet?
The conventional internet transmits information using classical bits. A bit has one of two values, 0 or 1, represented physically by electrical signals, light pulses, radio waves, or other measurable states. Networks encode these bits into data packets, route them between devices, and reconstruct the original information at its destination.
Quantum information is governed by a different set of rules. Its basic unit, the quantum bit or qubit, can be represented by a quantum system with two distinguishable states. Unlike a classical bit, a qubit can exist in a quantum superposition of those states, meaning its state cannot generally be described as simply one definite value or the other before measurement.
A qubit might be encoded in the polarization of a photon, the internal energy states of an atom, or the spin of an electron. These physical systems can exhibit quantum effects that have no direct equivalent in ordinary digital communication.
Superposition is one such effect, but two other properties are especially important for a quantum internet: entanglement and the limits of measuring or copying unknown quantum states.
Quantum entanglement is a relationship between quantum systems in which their joint state cannot be fully described by assigning each system its own independent quantum state. When two particles are entangled, measurements on them can reveal correlations that cannot be explained by classical physics alone.
The second property is that an unknown quantum state cannot be copied perfectly in general. This restriction, known as the no-cloning theorem, matters because conventional networks can copy digital data repeatedly to amplify signals, create backups, and forward packets. A quantum network cannot simply duplicate an arbitrary qubit whenever its signal becomes weak.
These differences do not make the quantum internet a universally faster or more powerful version of the existing internet. They make it useful for a different set of tasks. Ordinary networks remain far better suited to everyday activities such as browsing websites, streaming video, and transferring conventional files.
How quantum information could travel across a network
A practical quantum internet would combine quantum communication channels with ordinary classical communication. The quantum channels would carry quantum states, while classical channels would transmit instructions, measurement results, synchronization signals, and other information needed to coordinate the network.
One way to transmit quantum information is to encode it in photons and send those photons through optical fiber or, in some applications, through free space. Photons are natural carriers because they can travel long distances without the strong interactions with their surroundings that would quickly destroy many other quantum states.
However, even photons encounter problems. Optical fibers absorb some of the light passing through them, and other losses arise from imperfect equipment and connections. As the distance increases, the probability that a photon reaches its destination decreases.
In an ordinary optical network, repeaters can detect incoming signals, amplify them, and send stronger signals onward. This approach works because the network can regenerate classical information without needing to preserve the precise physical state of every photon.
Quantum communication is more demanding. Measuring an unknown quantum state can disturb it, and an unknown state cannot be perfectly copied. A conventional amplifier therefore cannot simply restore a weakened quantum signal while preserving all its quantum information.
This limitation is one of the main reasons researchers are developing quantum repeaters, devices designed to extend quantum communication over long distances without directly copying the quantum states being transmitted.
How quantum entanglement could connect distant devices
Entanglement could become one of the most valuable resources in a quantum internet. If two distant devices share an entangled pair, they can use the pair as a resource for communication protocols and distributed quantum operations.
The difficulty is creating and maintaining entanglement between systems separated by substantial distances.
Consider two quantum devices in different cities. Each could be connected to a nearby quantum communication node, and those nodes could attempt to establish entanglement using photons and local quantum memories. A quantum memory is a physical system capable of storing a quantum state long enough for the network to use it.
Once a suitable entangled connection exists between neighboring nodes, the network can attempt to extend the connection across additional links.
How quantum repeaters could extend entanglement
Suppose a network contains three nodes: A, B, and C. The goal is to establish entanglement between A and C, even though they are too far apart to establish a reliable direct connection.
First, the network establishes entanglement between A and B. Separately, it establishes entanglement between B and C. The two pairs are stored at the intermediate node B while the system prepares to connect them.
Node B can then perform a joint quantum measurement on its two local quantum systems. Under the appropriate protocol, this operation, called entanglement swapping, transfers the entanglement relationship to A and C.
The intermediate node does not need to send an intact copy of A’s quantum state to C. Instead, the network uses the entanglement already established on the two shorter links to create an entangled connection between the distant endpoints. Classical messages communicate the measurement outcome so the endpoints can interpret or use the resulting state correctly.
A long network can repeat this process across multiple segments. In principle, entanglement can be extended across many nodes without requiring a single photon to survive the entire distance.
Real systems must also contend with imperfect entanglement generation, losses, memory errors, and the time required to coordinate operations. Repeaters may need to store quantum states while waiting for other links to succeed. Because stored states can deteriorate, the timing and reliability of every operation matter.
Quantum repeaters are therefore not simply stronger versions of ordinary signal boosters. They are specialized systems that create, preserve, and connect entanglement through coordinated quantum operations.
Quantum teleportation: Sending a quantum state without sending the particle
Quantum teleportation is another important process that could support a quantum internet. Despite its name, it does not transport people or objects, and it does not move information faster than light.
Instead, quantum teleportation transfers an unknown quantum state from one physical system to another using shared entanglement and classical communication.
Imagine that a sender possesses a qubit in an unknown state and wants a distant receiver to obtain that state. The two parties first need to share an entangled pair. The sender performs a joint measurement involving the original qubit and the sender’s half of the entangled pair. This measurement produces a classical result, which the sender communicates to the receiver.
The receiver uses that result to determine which correction operation to perform on the receiver’s half of the entangled pair. Once the required steps are completed, the receiver’s qubit has the original quantum state.
The original state is not left intact at the sender’s location. The protocol transfers the state rather than creating a perfect duplicate of it.
Two details are essential. First, entanglement alone is not enough: the classical measurement result must also reach the receiver. Second, because this result travels through an ordinary communication channel, teleportation cannot transmit usable information faster than light.
For a quantum internet, teleportation offers a way to transfer quantum states between different physical systems. It can help connect devices that cannot exchange fragile quantum states directly and can support operations involving distant quantum processors.
Teleportation and entanglement swapping are closely related ideas, but they serve distinct purposes. Teleportation transfers a quantum state from one system to another, while entanglement swapping extends entanglement between systems that were not directly entangled with each other.
What a quantum internet could be used for
The value of a quantum internet would come from capabilities that depend on quantum physics, not from making every internet service faster. Several potential applications are especially significant.
More secure communication
One prominent application is quantum key distribution, a technique for establishing shared cryptographic keys between distant parties using quantum signals.
In a suitable quantum key distribution protocol, the sender and receiver encode information into quantum states and compare selected measurement results over a classical channel. The protocol can be designed so that attempts to intercept the quantum signals introduce detectable disturbances or other statistically measurable evidence of interference.
After testing the data and performing the required processing, the parties may establish a shared secret key. They can then use that key with an appropriate encryption system to protect ordinary messages.
The security advantage comes from the properties of quantum measurement and the ability to detect certain forms of eavesdropping. It does not mean that every system called quantum communication is automatically secure. Practical devices can have implementation weaknesses, and the classical communication, authentication procedures, software, and endpoint equipment must also be protected.
Quantum key distribution is also not the same as sending all information through quantum states. In many proposed systems, the quantum channel helps establish a key, while the actual messages travel over conventional networks.
A quantum internet could eventually support more sophisticated communication protocols that use entanglement as a resource. Nevertheless, quantum technology does not eliminate every cybersecurity threat or make encryption unnecessary.
Connecting quantum computers
Quantum computers process information using qubits and quantum operations. Some problems may benefit from quantum algorithms, but quantum computers are difficult to build and operate because qubits are sensitive to errors and environmental disturbances.
A quantum internet could connect separate quantum processors, allowing them to share entanglement or participate in distributed quantum operations. In some architectures, this could make it possible to divide a larger computational task among multiple quantum devices.
The challenge is substantial. Quantum computers cannot necessarily be linked together in the same way that ordinary computers are connected over a local network. A useful connection must preserve the relevant quantum states and support the operations required by the computation.
Researchers must also determine which tasks genuinely benefit from distributed quantum processing. Transferring quantum states and establishing entanglement consume resources, introduce errors, and require coordination. Connecting two quantum computers does not automatically give them the effective capacity of one larger machine.
Even so, networking could eventually make quantum computing more flexible by allowing specialized processors to interact rather than requiring every capability to reside in a single device.
Improving scientific measurements
Entanglement can also be useful in precision measurement. Quantum systems are used to study quantities such as time, magnetic fields, and acceleration, and certain quantum states can enable measurement strategies that outperform comparable classical approaches under specified conditions.
A quantum network could distribute entanglement among sensors at different locations. Those sensors might then perform coordinated measurements or compare quantum information in ways that would be difficult using independent instruments.
Potential applications include networks of precision clocks, distributed scientific instruments, and experiments that require carefully controlled quantum correlations across multiple locations.
These benefits are not automatic. The improvement depends on the measurement task, the quality of the entanglement, the noise affecting each sensor, and the design of the measurement procedure. A network that loses entanglement before useful data can be collected may offer little advantage over conventional techniques.
Why building a quantum internet is difficult
The underlying physics is established, but a dependable quantum network must overcome several interacting engineering problems.
Signal loss is a central obstacle. Photons can be absorbed or scattered as they travel through optical fiber. Over long distances, this makes direct transmission increasingly unreliable. Quantum repeaters could reduce the need for a single photon to cross the entire route, but their components must themselves work with sufficient efficiency and reliability.
Quantum states are fragile. Interactions with the surrounding environment can cause decoherence, the loss of the delicate quantum relationships needed for a protocol to work. Temperature changes, unwanted electromagnetic interactions, material defects, and imperfections in control systems can all contribute to errors, depending on the physical technology.
Quantum memories must preserve information. A repeater may need to store entanglement until another connection is ready. If the memory loses its quantum state too quickly, the network cannot reliably combine its links. Useful memories must balance storage time, efficiency, fidelity, and the ability to interact with the network’s communication hardware. Fidelity describes how closely a physical state or operation matches the intended one.
Different devices must work together. Photons are useful for communication, while atoms, ions, or other matter-based systems may be better suited to storing and processing quantum information. Transferring quantum states between these different physical systems is difficult. A network also needs compatible interfaces, synchronization, control software, and protocols that allow its components to cooperate.
The network must manage failures and uncertainty. Entanglement generation is often probabilistic: an attempt may succeed or fail. The network must track which links are available, preserve successful connections, coordinate operations, and respond to errors without accidentally using invalid quantum states. This requires a control architecture that combines classical computation with specialized quantum hardware.
Security introduces another layer of complexity. Quantum protocols can provide powerful protections under defined assumptions, but practical devices may deviate from those assumptions. A real network must address hardware imperfections, authentication, software vulnerabilities, and the possibility of attacks against implementation details.
No single breakthrough is likely to solve all these problems. Progress will depend on improvements in quantum sources, detectors, memories, repeater designs, error management, and network control.
How the quantum internet could coexist with the classical internet
A quantum internet would not need to replace the infrastructure already used to carry digital information. The two networks could share some physical infrastructure while serving different purposes.
Conventional networks would continue to handle ordinary data, including web traffic, video, email, and most computer-to-computer communication. Quantum channels would carry quantum states when an application needs them. Classical channels would coordinate the quantum operations, deliver measurement results, and manage the network.
This division is important because quantum states cannot simply be routed, copied, and inspected like ordinary packets. A quantum network must know which operations can safely be performed on a state, which nodes hold relevant entanglement, and whether the required resources are still available.
Some systems could use existing optical-fiber routes, but deploying quantum equipment on those routes would require careful engineering. Ordinary signals can introduce noise into quantum channels, and equipment designed for conventional communications may not be compatible with quantum-state transmission. Depending on the architecture, a network might require dedicated fibers, separate wavelengths, specialized interfaces, or other ways to isolate the quantum signals.
The eventual architecture will depend on the applications. A network designed mainly for quantum key distribution may have different requirements from one intended to connect quantum computers or support distributed sensing.
For that reason, the quantum internet is better understood as a family of network technologies and protocols than as a single finished system with one universal design.
What the quantum internet can and cannot do
A quantum internet could enable communication and computation that rely on entanglement, quantum-state transfer, and other quantum protocols. It may also make certain forms of cryptographic key distribution and distributed scientific measurement more practical.
It would not make ordinary messages travel faster than light. Entanglement produces correlations that cannot be explained by classical physics, but it cannot by itself transmit a controllable message between distant parties. Classical communication remains necessary for protocols such as quantum teleportation.
Nor would quantum networking make all communication unhackable. Security depends on the protocol, the equipment, the assumptions under which the system operates, and the protection of the classical infrastructure. Quantum cryptographic methods can address particular threats, but they do not remove the need for sound security engineering.
Finally, a quantum internet would not necessarily make every computation faster. Quantum processors are expected to be useful for particular classes of problems, and a network adds its own costs in communication, coordination, and error management. Some tasks may benefit from networking quantum devices; others will be better handled by conventional computers and networks.
The central promise is more specific: a quantum internet could allow distant quantum systems to share and use quantum information in ways that ordinary networks cannot reproduce. Turning that promise into a practical infrastructure will require not only control over individual quantum devices, but also reliable methods for connecting them across distances while preserving the properties that make quantum information valuable.