NationMaster - Encyclopedia: Fock state

Please help improve this article or section by expanding it.
Further information might be found on the talk page or at requests for expansion.
This article has been tagged since January 2007.

A Fock state, in quantum mechanics, is any state of the Fock space with a well-defined number of particles in each state. The name is for V. A. Fock. Image File history File links Wiki_letter_w. ... Fig. ... The Fock space is an algebraic system (Hilbert space) used in quantum mechanics to describe quantum states with a variable or unknown number of identical particles. ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... Vladimir Aleksandrovich Fock (or Fok, Владимир Александрович Фок) (22 December 1898 - December 27, 1974) was a Soviet physicist, who did foundational work on quantum mechanics. ...

If we limit to a single mode for simplicity (doing so we formally describe a mere harmonic oscillator), a Fock state is of the type $|nrangle$ with n an integer value. This means that there are n quanta of excitation in the mode. $|0rangle$ corresponds to the ground state (no excitation). It is different from 0 which is the null vector. In classical mechanics, a Harmonic oscillator is a system which, when displaced from its equilibrium position, experiences a restoring force proportional to the displacement according to Hookes law: where is a positive constant. ...

Fock states form the most convenient basis of the Fock space. They are defined to obey the following relations in the bosonic algebra: In linear algebra, a basis is a minimum set of vectors that, when combined, can address every vector in a given space. ... In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ...

$a^{dagger}|nrangle=sqrt{n+1}|n+1rangle$

$a|nrangle=sqrt{n}|n-1rangle$

$|nrangle={1oversqrt{n!}}(a^{dagger})^n|0rangle$

with a (resp. a^†) the annihilation (resp. creation) bose operator. Similar relations hold for fermionic algebra. In particle physics, fermions are particles with half-integer spin. ...

This allows to check that <a^†a>=n and Var(a^†a)=0, i.e., that measuring the number of particles a^†a in a Fock state returns always a definite value with no fluctuation.

Categories: Articles to be expanded since January 2007 | All articles to be expanded | Quantum mechanics | Quantum field theory | Quantum physics stubs Nonclassical light refers to states of light that can not be described using classical electromagnetism; its characteristics are described by the quantised electromagnetic field and quantum mechanics. ...

Results from FactBites:

coherent state: Information from Answers.com (1761 words)
	The coherent state's location in the complex plane (phase space) is centered at the position and momentum of a classical oscillator of the same phase θ and amplitude (or the same complex electric field value for an electromagnetic wave).
	Such coherent states are part of the explanation of effects such as the Quantum Hall effect in low-temperature superconducting semiconductors.
	In quantum field theory and string theory, a generalization of coherent states to the case of infinitely many degrees of freedom is used to define a vacuum state with a different vacuum expectation value from the original vacuum.

More results at FactBites »

COMMENTARY

Share your thoughts, questions and commentary here

Want to know more?
Search encyclopedia, statistics and forums:

Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m

See also GA_googleFillSlot("encyclopedia_square");

See also