Quantum cryptography

Quantum cryptography is the science of exploiting quantum mechanical properties to perform cryptographic tasks. The best known example of quantum cryptography is quantum key distribution which offers an information-theoretically secure solution to the key exchange problem. Currently used popular public-key encryption and signature schemes (e.g., RSA and ElGamal) can be broken by quantum adversaries. The advantage of quantum cryptography lies in the fact that it allows the completion of various cryptographic tasks that are proven or conjectured to be impossible using only classical (i.e. non-quantum) communication (see below for examples). For example, it is impossible to copy data encoded in a quantum state and the very act of reading data encoded in a quantum state changes the state. This is used to detect eavesdropping in quantum key distribution.

Quantum cryptography uses Heisenberg's uncertainty principle formulated in 1927, and the No-cloning theorem first articulated by Wootters and Zurek and Dieks in 1982. Werner Heisenberg invented one of the fundamental principles of quantum mechanics: "At the instant at which the position of the electron is known, its momentum therefore can be known only up to magnitudes which correspond to that discontinuous change; thus, the more precisely the position is determined, the less precisely the momentum is known, and conversely” (Heisenberg, 1927: 174–5). This simply means that observation of quanta changes its behavior. By measuring the velocity of quanta we would affect it, and thereby change its position; if we want to find a quant's position, we are forced to change its velocity. Therefore, we cannot measure a quantum system's characteristics without changing it (Clark, n.d.) and we cannot record all characteristics of a quantum system before those characteristics are measured. The No-cloning theorem demonstrates that it is impossible to create a copy of an arbitrary unknown quantum state. This makes unobserved eavesdropping impossible because it will be quickly detected, thus greatly improving assurance that the communicated data remains private.

...
Wikipedia