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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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

An international team of researchers has directly observed how angular momentum moves through a crystal lattice for the first time, revealing an unexpected quantum effect that causes the direction of rotation to reverse.

From Science Daily • May 24, 2026

The discovery, made using intense terahertz laser pulses, gives scientists a new view into the fundamental origins of magnetism and could eventually help researchers better control advanced quantum materials.

From Science Daily • May 24, 2026

Shares of GlobalFoundries, another company working on specialized chips for quantum computing, rose roughly 21%.

From The Wall Street Journal • May 23, 2026

The S&P 500 index saw its eighth straight week of gains, and the Dow industrials hit a record high on $2 billion in federal incentives for nine quantum computing companies.

From Barron's • May 22, 2026

Even if the zeros at the center of black holes don’t provide an easy way to travel through space, the zero of quantum mechanics provides an alternative: the zero-point energy might be the ultimate fuel.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife