Quantum fluctuation

A variation in a quantum system’s measurable properties arising from its probabilistic state and uncertainty relations. It can occur even in a system’s lowest-energy state.

Heisenberg uncertainty principle: A principle limiting how precisely certain pairs of physical quantities, such as position and momentum, can be jointly specified. Limits on jointly definite quantities underlie fluctuations in quantum states.
Casimir effect: An attraction between closely spaced conducting surfaces arising from changes in the quantum electromagnetic field’s allowed modes. It is a measurable force associated with altered vacuum fluctuations between surfaces.
Max Planck: German physicist whose 1900 work on black-body radiation introduced the quantum hypothesis. Planck’s quantization began the framework in which quantum fluctuations are described.
Thermal fluctuation: A variation in a system’s properties caused by its finite-temperature statistical distribution. Thermal fluctuations arise from heat, unlike fluctuations present in quantum ground states.
Quantum state: A mathematical description that encodes the possible outcomes and probabilities of measurements on a quantum system. Fluctuations depend on the probabilities encoded by the system’s state.
Lamb shift: A small splitting of hydrogen energy levels caused by interactions with the quantized electromagnetic field. Vacuum-field effects shift atomic energy levels in a measurable way.
Werner Heisenberg: German physicist who formulated matrix mechanics and the uncertainty principle. His uncertainty principle made intrinsic measurement spreads central to quantum theory.
Classical noise: Random variation in a classical signal or system, often caused by environmental or instrumental processes. Classical noise can mimic measured variation but does not require quantum uncertainty.
Quantum vacuum: The lowest-energy state of a quantum field, which need not have zero field values or zero fluctuations. Vacuum fluctuations are fluctuations of fields in their lowest-energy state.
Spontaneous emission: The transition of an excited atom or molecule to a lower-energy state while emitting a photon without an applied driving field. Quantum-field fluctuations help explain emission even without an external light field.

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