Opticalstate

Opticalstate is the quantum state of the electromagnetic field in a given optical mode. In quantum optics, light is quantized into modes of the field, each described by annihilation and creation operators a and a†, and by a Hilbert space of photon-number states. The state of the mode can be pure, described by a state vector |ψ⟩, or mixed, described by a density operator ρ.

Common families of optical states include coherent states, Fock states, squeezed states, and thermal states. Coherent states |α⟩ are eigenstates of a with eigenvalue α and exhibit Poissonian photon statistics; they closely resemble classical light produced by a stable laser. Fock states |n⟩ have a definite photon number and exhibit non-classical statistics. Squeezed states reduce quantum uncertainty in one field quadrature at the expense of the other, enhancing precision in measurements. Thermal states describe light in thermal equilibrium and have a diagonal density matrix in the Fock basis.

State characterization is often carried out by optical homodyne or heterodyne tomography to reconstruct quadrature distributions and to recover ρ or the Wigner function. Generation methods include spontaneous parametric down-conversion and four-wave mixing for nonclassical states, heralded single-photon sources, and feedback-based schemes in cavities.

Applications of optical states span quantum communication, quantum computation, metrology, and imaging. Nonclassical states enable secure communication via quantum key distribution and enhanced phase sensitivity in interferometry. The study of optical states connects fundamental quantum optics with practical technologies such as sensors and information processing.