Abstract
The fifth lesson addressed the question of how to measure entanglement by introducing the concepts of Shannon and von Neumann entropy. In a two-part system, the entropy associated with each part (calculated from their reduced density matrix) is a measure of the degree of entanglement. The existence of entanglement between the two parts thus appears as a loss of "local" information, the information being found in the non-local correlations between the parts. The essential link between entanglement, the second principle of thermodynamics and information theory was presented.
