Quantum optics

Quantum optics applies quantum theory to light and its interactions with matter, describing effects such as photon statistics, entanglement, and quantum measurement.

Photon: The quantum of the electromagnetic field, carrying energy and momentum in discrete amounts. Individual photons are the basic excitations whose states and statistics quantum optics studies.
Quantum state: A mathematical description that encodes the probabilities of outcomes for measurements on a quantum system. Quantum optics describes both light and matter through their quantum states.
Laser: A device that produces coherent light through stimulated emission and optical feedback. Laser fields provide controllable quantum states and drive many optical experiments.
Classical optics: The description of light using classical electromagnetic fields and their propagation. It explains many optical phenomena but cannot capture effects such as antibunching.
Roy J. Glauber: An American physicist who developed a quantum theory of optical coherence and photodetection. His formalism established a systematic framework for quantum-optical correlations and measurements.
Quantum harmonic oscillator: A quantum system with equally spaced energy levels and dynamics analogous to a classical harmonic oscillator. Each mode of the electromagnetic field behaves mathematically like a quantum harmonic oscillator.
Fock state: A state with a definite number of particles or excitations in a mode. Photon-number states make discrete particle properties explicit.
Single-photon source: A device that emits photons one at a time with controlled timing and properties. Reliable single photons enable experiments and protocols requiring discrete optical quanta.
Photon antibunching: A reduction in the probability of detecting photons close together in time compared with random arrivals. Antibunching is a nonclassical signature that distinguishes single-photon light from classical fields.
John Clauser: An American physicist known for experiments testing Bell inequalities with entangled photons. His photon experiments connected quantum-optical sources and measurements to tests of quantum foundations.

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