Coherent state

A quantum state whose field amplitudes and fluctuations most closely resemble those of a classical oscillating wave. It is an eigenstate of the annihilation operator and has Poisson-distributed particle number.

Annihilation operator: A quantum operator that lowers the occupation number of a mode by one. A coherent state is an eigenstate of this operator, with its eigenvalue giving the field amplitude.
Quantum optics: The study of light using quantum theory, including its interactions with matter and measurement. Coherent states are a central state description in this field.
Laser: A device that produces light through stimulated emission, commonly yielding a beam with coherent-state-like statistics. An ideal laser output is often modeled as a coherent state.
Erwin Schrödinger: A physicist who formulated wave mechanics and introduced the equation governing nonrelativistic quantum states. His 1926 work described oscillator wave packets that retain their shape during motion.
Thermal state: A statistical quantum state describing a system in thermal equilibrium at a specified temperature. Thermal light has broader number fluctuations than the Poissonian statistics of coherent light.
Poisson distribution: A discrete probability distribution whose mean equals its variance. Measurements of particle number in a coherent state follow this distribution.
Fock state: A state with a definite number of particles in a quantum mode. It contrasts with coherent states, which have uncertain particle number.
Homodyne detection: A measurement technique that mixes a signal with a phase-controlled reference field to measure a field quadrature. Its strong reference beam is commonly treated as a coherent state.
Roy J. Glauber: A physicist who developed the quantum theory of optical coherence and introduced coherent states into quantum optics. His 1963 formulation established coherent states as tools for describing light.
Squeezed state: A quantum state with reduced uncertainty in one field quadrature and increased uncertainty in its conjugate quadrature. It can improve precision beyond coherent-state noise in one measurement direction.

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