Ground State

The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. The ground state of a quantum field theory is usually called the vacuum state or the vacuum.

If more than one ground state exists, they are said to be degenerate. Many systems have degenerate ground states. It turns out that degeneracy occurs whenever a nontrivial unitary operator commutes with the Hamiltonian of the system.

According to the third law of thermodynamics, a system at absolute zero temperature exists in its ground state; thus, its entropy is determined by the degeneracy of the ground state. Many systems, such as a perfect crystal lattice, have a unique ground state and therefore have zero entropy at absolute zero. It is also possible for the highest excited state to have absolute zero temperature for systems that exhibit negative temperature.

Read more about Ground State:  Examples

Famous quotes containing the words ground and/or state:

    When all is said and done, friendship is the only trustworthy fabric of the affections. So-called love is a delirious inhuman state of mind: when hot it substitutes indulgence for fair play; when cold it is cruel, but friendship is warmth in cold, firm ground in a bog.
    Miles Franklin (1879–1954)

    I incline to think that the people will not now sustain the policy of upholding a State Government against a rival government, by the use of the forces of the United States. If this leads to the overthrow of the de jure government in a State, the de facto government must be recognized.
    Rutherford Birchard Hayes (1822–1893)