A qubit, or quantum bit, is the fundamental unit of quantum information. Unlike a classical bit that is restricted to being in a state of either 0 or 1, a qubit can exist in a superposition of both states simultaneously. This property, along with entanglement, allows quantum computers to perform certain calculations exponentially faster than classical computers by processing massive amounts of information in parallel.
The term 'qubit' was coined by Benjamin Schumacher in 1995 in a conversation with William Wootters, though the concept of two-state quantum systems dates back to the early days of quantum mechanics. The realization of physical qubits has been pursued since the 1990s using various technologies like trapped ions and superconducting circuits.
Qubits are central to the development of quantum computing, a field that is receiving billions in investment from governments and tech giants like Google, IBM, and Rigetti. The race is on to build stable, error-corrected qubits (logical qubits) to solve real-world problems in chemistry, materials science, and cryptography.