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:
“A State, in idea, is the opposite of a Church. A State regards classes, and not individuals; and it estimates classes, not by internal merit, but external accidents, as property, birth, etc. But a church does the reverse of this, and disregards all external accidents, and looks at men as individual persons, allowing no gradations of ranks, but such as greater or less wisdom, learning, and holiness ought to confer. A Church is, therefore, in idea, the only pure democracy.”
—Samuel Taylor Coleridge (1772–1834)
“Ireland still remains the Holy Isle whose aspirations must on no account be mixed with the profane class-struggles of the rest of the sinful world ... the Irish peasant must not on any account know that the Socialist workers are his sole allies in Europe.”
—Friedrich Engels (1820–1895)
“Today’s difference between Russia and the United States is that in Russia everybody takes everybody else for a spy, and in the United States everybody takes everybody else for a criminal.”
—Friedrich Dürrenmatt (1921–1990)