Quantum network

Quantum networks form an important element of quantum computing and quantum cryptography systems. Quantum networks allow for the transportation of quantum information between physically separate quantum systems. In distributed quantum computing, network nodes within the network can process information by serving as quantum logic gates. Secure communication can be implemented using quantum networks through quantum key distribution algorithms.

Optical quantum networks using fiber optic links or free-space links play an important role transmitting quantum states in the form of photons across large distances. Optical cavities can be used to trap single atoms and can serve as storage and processing nodes in these networks.

Many existing quantum networks are designed to support quantum key distribution (QKD) between classical computing environments. In this application, the quantum network facilitates the sharing of a secret encryption key between two parties. Unlike classical key distribution algorithms such as Diffie-Hellman key exchange, quantum key distribution provides security through physical properties rather than the difficulty of a mathematical problem.

The first quantum key distribution protocol, BB84, was proposed by Charles Bennett and Gilles Brassard in 1984 and has been implemented in a number of research quantum networks. In this protocol, qubits are sent from one party to another over an insecure quantum network. Due to the properties of quantum mechanics and the no-cloning theorem, it is impossible for an eavesdropper to determine the key without being detected by the sender and receiver.

While the BB84 protocol relies on the superposition of qubit states to detect eavesdropping, other protocols use entangled qubits. Examples of these protocols include the E91 protocol proposed by Artur Ekert, and the BBM92 protocol proposed by Charles H. Bennett, Gilles Brassard, and N. David Mermin.

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