quantum

American  

[kwon-tuhm] / ˈkwɒn təm /

noun

quanta plural

1. quantity or amount.

   the least quantum of evidence.

2. a particular amount.

3. a share or portion.

4. a large quantity; bulk.

5. Physics.

   1. the smallest quantity of radiant energy, equal to Planck's constant times the frequency of the associated radiation.

   2. the fundamental unit of a quantized physical magnitude, as angular momentum.

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adjective

1. sudden and significant.

   a quantum increase in productivity.

quantum British  

/ ˈkwɒntəm /

noun

1. physics

   1. the smallest quantity of some physical property, such as energy, that a system can possess according to the quantum theory

   2. a particle with such a unit of energy

2. amount or quantity, esp a specific amount

3. (often used with a negative) the least possible amount that can suffice

   there is not a quantum of evidence for your accusation

4. something that can be quantified or measured

5. (modifier) loosely, sudden, spectacular, or vitally important

   a quantum improvement

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quantum Scientific  

/ kwŏn′təm /

quanta plural

1. A discrete, indivisible manifestation of a physical property, such as a force or angular momentum. Some quanta take the form of elementary particles; for example, the quantum of electromagnetic radiation is the photon, while the quanta of the weak force are the W and Z particles.

2. See also quantum state

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Other Word Forms

Derived Forms

• quantumness
  noun

Inflected Forms

Nouns

• quanta
  plural

Etymology

Origin of quantum

1610–20; noun use of neuter of Latin quantus how much

Explanation

While quantum refers to a general quantity or size, it is most often used in physics as a measure of the smallest amount of something — usually energy — that something can possess. The plural form is quanta. In the 17th century, the word quantum, from the Latin word for "how much," referred to a portion. Quantum is usually a noun referring to a specific amount of something. However, it can also be used as an adjective, as in the phrase "quantum leap," where it refers to a sudden, important change. Outside of physics, the word might be used with "not" to refer to something insignificant, as in "There's not a quantum of truth in what you say."

Example Sentences

Alongside Canada, they are trying to create AI platforms and quantum computing systems that won’t be under American control.

From The Wall Street Journal • Jul. 9, 2026

According to Prof. Schmidt, the new theory provides a versatile way to describe quantum impurities across different spatial dimensions and a wide variety of interactions.

From Science Daily • Jul. 9, 2026

The new framework also naturally explains how quantum systems transition between so called polaronic and molecular states.

From Science Daily • Jul. 9, 2026

The theoretical framework behind the experiment was developed by Innsbruck quantum physicist Peter Zoller and his colleagues.

From Science Daily • Jul. 8, 2026

Now, by Planck’s quantum hypothesis, one cannot use an arbitrarily small amount of light; one has to use at least one quantum.

From "A Brief History of Time: And Other Essays" by Stephen Hawking