Quantum information science

Quantum information science studies how information is represented, processed, transmitted, and measured using quantum systems. It combines quantum physics with information theory and computation.

Qubit: A two-level quantum system used as the basic unit of quantum information. Qubits encode quantum information and can occupy superpositions of computational states.
Quantum computing: Computation that uses quantum states and operations to process information. It is the most visible computational branch of quantum information science.
Quantum mechanics: The physical theory describing matter and energy at atomic and subatomic scales. Its laws determine how quantum information can be encoded and manipulated.
Classical information: Information represented by distinguishable symbols or states governed by classical probability. It provides the baseline against which quantum encoding and processing are compared.
Quantum error correction: Methods for protecting quantum information by encoding it across multiple physical systems. It addresses errors without directly measuring and destroying the encoded information.
Quantum gate: A reversible operation that transforms the state of one or more qubits. Gate sequences implement quantum computations by changing encoded states.
Quantum cryptography: The use of quantum principles to support cryptographic tasks, especially secure key distribution. Quantum communication protocols can reveal eavesdropping through disturbances in transmitted states.
Information theory: The mathematical study of information representation, transmission, and uncertainty. It provides concepts such as entropy, channel capacity, and coding for quantum extensions.
Classical computing: Computation performed using classical bits and physical operations on them. Its bit-based model differs from quantum computation but remains faster for many practical tasks.
Quantum fault tolerance: The ability to perform arbitrarily long quantum computations despite imperfect components, within specified error bounds. It defines conditions under which error-corrected quantum computing can scale reliably.

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