Quantum Jargon Glossary

The fundamental unit of quantum information, analogous to the classical bit. Unlike a classical bit which must be in state 0 or 1, a qubit can exist in a superposition of both states simultaneously.

A principle of quantum mechanics that allows a quantum system to be in multiple states at the same time until it is measured. For a qubit, this means being in a linear combination of |0⟩ and |1⟩.

A quantum phenomenon where two or more particles become correlated in such a way that the quantum state of each particle cannot be described independently of the others, even when separated by large distances.

The loss of quantum coherence in a quantum system, typically caused by interaction with the external environment. This leads to quantum noise and causes qubits to lose their quantum behavior and return to classical states.

A single-qubit quantum logic gate that maps the basis state |0⟩ to (|0⟩ + |1⟩)/√2 and |1⟩ to (|0⟩ - |1⟩)/√2, creating an equal superposition of the two basis states.

Controlled-NOT gate. A multi-qubit gate that performs a Pauli-X (NOT) operation on a target qubit only if the control qubit is in state |1⟩. It is commonly used to create entangled states.

Noisy Intermediate-Scale Quantum. The current era of quantum computing where processors contain 50 to a few hundred qubits but lack full quantum error correction, meaning they are prone to noise and errors.

Also called quantum advantage. The milestone demonstrating that a quantum computer can solve a specific calculation that is practically impossible for any classical supercomputer to solve in a reasonable timeframe.

An open-source software development kit created by IBM for working with quantum computers at the level of circuits, pulses, and algorithms. It is written in Python.

A set of techniques used to protect quantum information from noise, decoherence, and operational errors by encoding logical qubits into larger groups of physical qubits.

A geometrical representation of the pure state space of a two-level quantum mechanical system (a qubit). The poles represent the classical states |0⟩ and |1⟩, and the surface represents all pure superposition states.

A device used to maintain extremely low temperatures. Superconducting quantum computers require cryostats (dilution refrigerators) to cool their quantum processors down to near absolute zero (~15 millikelvin).