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Quantum information studies methods of encoding, transmitting, and processing data using quantum systems. Unlike classical information, quantum information cannot be arbitrarily copied (no-cloning theorem) and can be compressed in new ways. The main resources are superposition and entanglement. They allow the implementation of algorithms that have no classical analogs in efficiency, for example, integer factorization (Shor's algorithm) and database search (Grover's algorithm). Quantum entanglement also provides absolutely secure key distribution (BB84 protocol).

History

The idea of quantum computing was put forward in the 1980s: Richard Feynman realized that quantum systems are hard to simulate on classical computers, and David Deutsch built the first model of a universal quantum machine.

How it works

A qubit is, for example, an atom that can be excited by a laser. The laser puts it into a superposition state (a mixture of unexcited and excited). Two atoms are entangled through interaction. Then a system of many qubits evolves according to the algorithm, and at the end a measurement yields the answer. Importantly, the computation process itself is a careful manipulation of quantum interference, like tuning a musical instrument.

💡 The no-cloning theorem states that it is impossible to create an identical copy of an arbitrary unknown quantum state — nature sets a limit on copying.
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Scientists
David DeutschJohn Stewart BellJohn Archibald Wheeler
Related tags
density matrixFourier seriesHilbert spacequantum algorithmquantum computerquantum entanglementquantum error correctionquantum key distribution
Laws
no-cloning theoremquantum Hall effect

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