What does quantum mean?
A quantum is the smallest discrete amount in which certain physical properties, such as energy or angular momentum, can be transferred. The idea is central to quantum mechanics, which describes the behaviour of matter and light at atomic and subatomic scales. Outside physics, “a quantum of” can mean a small amount of something abstract, such as time, comfort, or hope. As an adjective, quantum commonly refers to quantum mechanics, quantum physics, quantum computing, or quantum communication. The word comes from Latin, where quantum meant “how much,” an appropriate reminder that modern quantum theory is concerned with precisely measuring quantities at the smallest possible scale. The term is useful because it distinguishes the indivisible units that underpin quantum physics from the continuous quantities familiar from everyday, classical physics.
A discrete, indivisible unit of a physical quantity, especially a unit of energy or another measurable property in quantum mechanics. In general use, it can also mean a very small amount of something.
"The detector recorded a single quantum of light."
The general sense “a small amount” is formal and literary; the physics sense is the most technically specific.
Relating to quantum theory, quantum mechanics, or quantum phenomena.
"Quantum computing may eventually transform the way certain problems are solved."
Most commonly used in established technical compounds such as quantum mechanics, quantum physics, and quantum computing.
The plural quanta is standard in physics, especially for the discrete units of energy or matter discussed in quantum theory.
"The experiment generated and detected individual quanta of light."
The word “quantum” means “how much” in Latin, but in modern physics it also means something too small to divide any further.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does quantum come from?
The word comes from the Latin quantus, meaning “how much,” through the neuter form quantum, meaning “how much.” The Latin word is also the source of related English forms such as quantity, quantify, and quantitative. Quantum was used in English for an amount or portion before acquiring its dominant modern association with the indivisible units described by quantum theory.
Related word forms
How quantum is actually used
In general use, “a quantum of” is formal and slightly literary, meaning a very small amount. As an adjective, “quantum” is most commonly associated with physics and quantum technology, especially quantum computing, quantum communication, and quantum mechanics.
Easily confused with quantum
A quantity is the amount or measurable property of something, whereas a quantum is specifically a discrete unit in quantum physics.