quantumcommunication

Quantum communication is the use of quantum states to encode, transmit and process information. Unlike classical communication, it leverages quantum properties such as superposition and entanglement to achieve tasks that are difficult or impossible classically. A central goal is secure information transfer, enabled by the no-cloning theorem and the laws of quantum mechanics, which prevent perfect copying of unknown quantum states and guarantee security in certain protocols.

Quantum key distribution (QKD) is the best-known application, providing provably secure keys via protocols such as BB84 and Ekert 1991. In BB84, sender encodes bits into non-orthogonal quantum states; the receiver measures in random bases; any eavesdropping introduces disturbance detectable by the legitimate parties. The Ekert scheme uses entangled pairs and Bell inequality violations to ensure security.

Quantum teleportation allows transferring a quantum state from one location to another without moving the physical system, using pre-shared entanglement and classical communication; it is a foundational primitive for quantum networks and repeaters.

Channels include optical fibers and free-space links carrying photons; satellite-based links extend reach. To overcome loss in long-distance fiber, quantum repeaters and quantum memories are proposed to enable quantum networks and eventually a quantum internet.

Current status: laboratory demonstrations and field tests have verified QKD and entanglement distribution across various platforms; commercial QKD systems exist; research focuses on scalability, device-independent security, integration with classical networks, and standardization.

Outlook: quantum communication aims to form quantum networks enabling secure communication, distributed quantum computing, and enhanced sensing.