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:
“We are in fact convinced that if we are ever to have pure knowledge of anything, we must get rid of the body and contemplate things by themselves with the soul by itself. It seems, to judge from the argument, that the wisdom which we desire and upon which we profess to have set our hearts will be attainable only when we are dead and not in our lifetime.”
—Socrates (469–399 B.C.)
“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)
“During the first World War women in the United States had a chance to try their capacities in wider fields of executive leadership in industry. Must we always wait for war to give us opportunity? And must the pendulum always swing back in the busy world of work and workers during times of peace?”
—Mary Barnett Gilson (1877–?)