In *quantum communication*, the main idea is to transfer information in a better way than with classical means using quantum mechanical concepts like [[Entanglement|entanglement]] or the [[No-Cloning Theorem|no-cloning theorem]]. Better can mean a lot of things. Let us focus here on one interpretation: it could be more secure. ![[quantum_communication.excalidraw.light.svg]] One of the major fears stoked by quantum computing is the breaking of [[Encryption|cryptographic algorithm]]. Most cryptographic methods are based on the idea of a [[Trapdoor function|trapdoor function]]: It is easy to fall in, but hard to get out. In more technical terms: one direction of the computation is easy, but reverting it is very hard. As an example, we can easily multiply two numbers, but figuring out which two numbers are the factors of 67280421310721 is much harder. In cryptographic algorithms, we use the easy direction to encrypt/decrypt data with a key, but an attacker has to solve the hard problem, since they are missing the key. In the sense of better is more secure, quantum communication uses quantum effects to transfer keys securely between two parties. This process is called [[Quantum Key Distribution|quantum key distribution]]. The main quantum effect that is used here is the [[no-cloning theorem]]: arbitrary quantum information cannot be copied! Thus, any eavesdropper who tries to steal the key will disrupt the communication and can be detected. Quantum communication in general, however, has much more to offer than just more secure communication. An important part is the design of [[Quantum Network|quantum networks]], an idea similar to the Internet, just for [[Quantum Information|quantum information]]. These networks enable applications like [[Blind Quantum Computing|blind quantum computing]] and improved communication protocols. Superdense coding, for example, leverages entanglement to transmit the same amount of information using fewer quantum bits, making communication more efficient. >[!read]- Further Reading >- [[Quantum Network]] >- [[Encryption]] >- [[Alice and Bob]] >- [[Quantum Repeater]] >[!ref]- References >- H. Buhrman, Ł. Czekaj, A. Grudka, M. Horodecki, P. Horodecki, M. Markiewicz, F. Speelman, and S. Strelchuk, Quantum communication complexity advantage implies violation of a Bell inequality, Proceedings of the National Academy of Sciences **113**, 3191 (2016). >- H. Buhrman and H. Röhrig, _Distributed Quantum Computing_, in _Mathematical Foundations of Computer Science 2003_, edited by B. Rovan and P. Vojtáš (Springer, Berlin, Heidelberg, 2003), pp. 1–20. >- H. J. Kimble, The quantum internet, Nature **453**, 1023 (2008).