Fock state

Fock states ( named after the physicist Vladimir Aleksandrovich Fock ) are in the quantum-mechanical many-body theory and quantum field theory states of certain particles in the so-called Fock space that can serve there as a base.

Generally a distinction is made between particles

• Fermions ( with half-integer spin) and
• Bosons ( integer spin ).

They differ mainly by the commutation relations of them performing operators, their quantum statistics:

• Fermions ( such as electrons ) can according to the Fermi -Dirac statistics a state with the same quantum numbers ( including their spin orientation is one ) either not at all or only once occupy
• When bosons ( as photons or phonons) there is according to the Bose -Einstein statistics no restriction on the number of particles in a given state.

States in the Fock space can be constructed with the help of creation and annihilation operators. This is also called occupation number representation or Second quantization.

In the Fock space also states can be constructed in which the particle number is given only in the middle and may fluctuate around the mean, for example coherent states in laser physics.

• Quantum field theory