Example 11.10: Entropy as measure of entanglement The von Neumann entropy S is given by the relation S = −kTrρ ln ρ = −kΣiρi ln ρi, (11.78)

and provides a measure of the departure from a pure state (in which case S = 0). An eigenvalue

(i.e. diagonalized element) ρi describes the probability that the system represented by the density