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 and, pure, mixed and/or states:
“The spirit of the world, the great calm presence of the creator, comes not forth to the sorceries of opium or of wine. The sublime vision comes to the pure and simple soul in a clean and chaste body.”
—Ralph Waldo Emerson (1803–1882)
“... pure and intelligent women can be deceived and misled by the baser sort, their very innocence and experience making them credulous and the helpless tools of the guilty and bold.”
—Catherine E. Beecher (1800–1878)
“There are certain queer times and occasions in this strange mixed affair we call life when a man takes this whole universe for a vast practical joke, though the wit thereof he but dimly discerns, and more than suspects that the joke is at nobody’s expense but his own.”
—Herman Melville (1819–1891)
“On 16 September 1985, when the Commerce Department announced that the United States had become a debtor nation, the American Empire died.”
—Gore Vidal (b. 1925)