Pure and Mixed States
In quantum mechanics, a quantum system is represented by a state vector (or ket) . A quantum system with a state vector is called a pure state. However, it is also possible for a system to be in a statistical ensemble of different state vectors: For example, there may be a 50% probability that the state vector is and a 50% chance that the state vector is . This system would be in a mixed state. The density matrix is especially useful for mixed states, because any state, pure or mixed, can be characterized by a single density matrix.
A mixed state is different from a quantum superposition. In fact, a quantum superposition of pure states is another pure state, for example .
Read more about this topic: Density Matrix
Famous quotes containing the words pure, mixed and/or states:
“The Family is the Country of the heart. There is an angel in the Family who, by the mysterious influence of grace, of sweetness, and of love, renders the fulfilment of duties less wearisome, sorrows less bitter. The only pure joys unmixed with sadness which it is given to man to taste upon earth are, thanks to this angel, the joys of the Family.”
—Giuseppe Mazzini (1805–1872)
“Let us not deny it up and down. Providence has a wild, rough, incalculable road to its end, and it is of no use to try to whitewash its huge, mixed instrumentalities, or to dress up that terrific benefactor in a clean shirt and white neckcloth of a student of divinity.”
—Ralph Waldo Emerson (1803–1882)
“The end of law is not to abolish or restrain, but to preserve and enlarge freedom. For in all the states of created beings capable of laws, where there is no law, there is no freedom.”
—John Locke (1632–1704)