The term "qubit" is a portmanteau of "quantum" and "bit." It was coined to describe the quantum analog of classical bits, which are the basic units of classical information. The concept of a qubit was introduced in the early 1980s by Benioff, Feynman, and others as quantum computing and information theory emerged.
The choice of the term "qubit" reflects the close connection between classical information theory and quantum information theory. Classical bits represent information as binary digits, where each bit can be in one of two states: 0 or 1. In quantum computing, qubits represent the quantum version of bits, but with the added ability to exist in superpositions of states.
The "q" in "qubit" signifies its quantum nature, while "ubit" comes from "bit," indicating its role as the quantum counterpart of a classical bit. This term effectively captures the essence of a quantum system that can store and process information using quantum principles.
The naming convention of combining the prefix "q-" or "quantum" with existing classical terms is also observed in other areas of quantum information, such as "qutrit" (quantum analog of a classical trit), "qudit" (quantum analog of a classical d-digit), and "quantum gate" (analogous to classical logic gates).
Overall, the term "qubit" was introduced to denote the fundamental unit of quantum information and to highlight its relation to classical bits while emphasizing its distinctive quantum properties.