Ground state (nonfiction): Difference between revisions
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An [[Excited state (nonfiction)|excited state]] is any state with energy greater than the ground state. In quantum field theory, the ground state is usually called the vacuum state or the vacuum. | An [[Excited state (nonfiction)|excited state]] is any state with energy greater than the ground state. In quantum field theory, the ground state 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 energy levels (nonfiction)|degenerate ground states]]. Degeneracy occurs whenever there exists a [[Unitary operator (nonfiction)|unitary operator]] that acts non-trivially on a ground state and commutes with the Hamiltonian of the system. | If more than one ground state exists, they are said to be degenerate. Many systems have [[Degenerate energy levels (nonfiction)|degenerate ground states]]. Degeneracy occurs whenever there exists a [[Unitary operator (nonfiction)|unitary operator]] that acts non-trivially on a ground state and [[Commutator (nonfiction)|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. | 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. | ||
Revision as of 10:12, 20 September 2021
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.
Description
An excited state is any state with energy greater than the ground state. In quantum field theory, the ground state 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. Degeneracy occurs whenever there exists a unitary operator that acts non-trivially on a ground state and 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.
In the News
Fiction cross-reference
Nonfiction cross-reference
- Excited state (nonfiction)
- Physics (nonfiction)
- Unitary operator (nonfiction)
- Zero-point energy (nonfiction)
External links
- Ground state @ Wikipedia