- #1

hellfire

Science Advisor

- 1,047

- 1

## Main Question or Discussion Point

When reading in the web about decoherence especially in popular articles I find very often explanations that point out the fact that the enviroment has a large number of degrees of freedom. It is unclear to me in which extent and in which aspects this is relevant for decoherence.

My understanding is that when one has a system A in a pure state that interacts with another system B, leading to an entangled state between A and B, the reduced density matrix of the subsystem A will always describe a mixed state, provided that the states of the subsystem B are orthonormal.

If this is correct, the fact that decoherence arises is independent of the number of degrees of freedom of B.

My understanding is that when one has a system A in a pure state that interacts with another system B, leading to an entangled state between A and B, the reduced density matrix of the subsystem A will always describe a mixed state, provided that the states of the subsystem B are orthonormal.

If this is correct, the fact that decoherence arises is independent of the number of degrees of freedom of B.