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:
“A man’s social and spiritual discipline must answer to his corporeal. He must lean on a friend who has a hard breast, as he would lie on a hard bed. He must drink cold water for his only beverage. So he must not hear sweetened and colored words, but pure and refreshing truths. He must daily bathe in truth cold as spring water, not warmed by the sympathy of friends.”
—Henry David Thoreau (1817–1862)
“I was glad to have got out of the towns, where I am wont to feel unspeakably mean and disgraced,—to have left behind me for a season the bar-rooms of Massachusetts, where the full-grown are not weaned from savage and filthy habits,—still sucking a cigar. My spirits rose in proportion to the outward dreariness. The towns needed to be ventilated. The gods would be pleased to see some pure flames from their altars. They are not to be appeased with cigar-smoke.”
—Henry David Thoreau (1817–1862)
“Memory is a wonderfully useful tool, and without it judgement does its work with difficulty; it is entirely lacking in me.... Now, the more I distrust my memory, the more confused it becomes. It serves me better by chance encounter; I have to solicit it nonchalantly. For if I press it, it is stunned; and once it has begun to totter, the more I probe it, the more it gets mixed up and embarrassed. It serves me at its own time, not at mine.”
—Michel de Montaigne (1533–1592)
“How many people in the United States do you think will be willing to go to war to free Estonia, Latvia, and Lithuania?”
—Franklin D. Roosevelt (1882–1945)