quantum

Pluralquantums, quanta

1. 1
   adjective

   Relating to quanta, quantum mechanics, or technologies based on quantum physics, including quantum computers.

   Quantum effects such as tunneling let particles slip through barriers they could not cross in classical physics.

   For decades, physicists have tried to reconcile gravity with quantum theory.

   Oppositeclassical

   Note

   Its opposite in physics is classical: classical rules describe everyday objects well, while quantum rules govern atoms, light and other very small systems. The adjective labels whole theories, such as quantum mechanics, quantum electrodynamics and quantum gravity, the last two of which Michael Riordan describes in American Scientist (2012) as dogged for decades by infinities. Source

   Checked 1 Nov 2026 · 5 facts

   • Classical is the contrasting term for quantum in physics. en.wiktionary.org
   • Classical physics describes everyday objects well. nist.gov
   • Quantum physics governs atoms, light and other microscopic systems. nist.gov
   • Michael Riordan wrote the cited American Scientist article in 2012. en.wiktionary.org
   • Riordan's statement names quantum electrodynamics and quantum gravity; it does not include quantum mechanics. en.wiktionary.org
2. 2
   adjectivecolloquial

   Of a change or advance, sudden and very large or significant, rather than gradual.

   The new engine represents a quantum leap in fuel efficiency.

   Remote work has brought a quantum shift in how companies think about office space.

   UsageMostly in quantum leap and quantum shift; careful writing often prefers major or dramatic.

   Similargiant, dramatic, massive, huge, radical

   Oppositegradual, incremental

   Note

   Everyday English turns the physics around: a quantum leap or a quantum shift is a big change, although the physicist's quantum is the smallest discrete amount of a given physical quantity.

3. 3
   smallest unitnouncountable or uncountable

   The smallest possible unit of a given quantity or measurable phenomenon, which for that reason cannot be divided.

   An electron moves between energy levels by absorbing or emitting a single quantum.

   Light is absorbed and emitted only in whole quanta, never in fractions of one.

   UsageThe plural is usually quanta.

   Note

   Physicists write the plural quanta, keeping the Latin form, though quantums also exists. A quantum of light is a photon, and the discovery that light is emitted and absorbed in such packets helped give the physics of the very small its name. Source

   Checked 1 Nov 2026 · 5 facts

   • Quanta and quantums are plural forms of quantum. en.wiktionary.org
   • Quanta preserves a Latin form. en.wiktionary.org
   • A quantum of light is a photon. en.wikipedia.org
   • Energy is not always quantized: a free particle can have a continuous range of energies. The statement should specify the emission and absorption of light. cpb-us-e1.wpmucdn.com
   • Quantum physics takes its name from the discovery of quantization. renyi.hu
4. 4
   computing fieldnoununcountableabbreviationellipsis

   Short for quantum computing: the field of building and using computers that run on quantum physics.

   Investors are pouring money into quantum, hoping for a breakthrough within the decade.

   The startup hires physicists and software engineers who want a career in quantum.

   UsageAs a field name it takes no article: work in quantum, like work in finance.

5. 5
   nouncountable or uncountable

   The amount or extent of something, especially in law, the amount of damages awarded or the severity of a sentence.

   The ministry approved the fare hike, but the quantum of the increase is still being debated.

   Auditors are still working out the quantum of funds diverted from the project.

   UsageUsually the quantum of something: the quantum of damages.

   Similaramount, extent, quantity, size

   Note

   Latin quantus, "how much", is the root, and this was once an ordinary English word: Henry Fielding's narrator in Tom Jones (1749) declines to reveal "the quantum of this present". Today it belongs to formal writing and to law, where courts across Britain and the Commonwealth assess the quantum of damages, and it is common in South Asian English, where the Times of India can report that "the quantum of increase emerged as a hitch".

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