Definition
A more mathematical definition is that Fock states are those elements of a Fock space which are eigenstates of the particle number operator. Elements of a Fock space which are superpositions of states of differing particle number (and thus not eigenstates of the number operator) are, therefore, not Fock states. Thus, not all elements of a Fock space are referred to as "Fock states."
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 with n an integer value. This means that there are n quanta of excitation in the mode. corresponds to the ground state (no excitation). It is different from 0, which is the null vector.
Fock states form the most convenient basis of the Fock space. They are defined to obey the following relations in the bosonic algebra:
with (resp. ) the annihilation (resp. creation) bose operator. Similar relations hold for fermionic algebra.
This allows to check that and, i.e., that measuring the number of particles in a Fock state returns always a definite value with no fluctuation.
Read more about this topic: Fock State
Famous quotes containing the word definition:
“It is very hard to give a just definition of love. The most we can say of it is this: that in the soul, it is a desire to rule; in the spirit, it is a sympathy; and in the body, it is but a hidden and subtle desire to possessafter many mysterieswhat one loves.”
—François, Duc De La Rochefoucauld (16131680)
“Mothers often are too easily intimidated by their childrens negative reactions...When the child cries or is unhappy, the mother reads this as meaning that she is a failure. This is why it is so important for a mother to know...that the process of growing up involves by definition things that her child is not going to like. Her job is not to create a bed of roses, but to help him learn how to pick his way through the thorns.”
—Elaine Heffner (20th century)
“... we all know the wags definition of a philanthropist: a man whose charity increases directly as the square of the distance.”
—George Eliot [Mary Ann (or Marian)