entropy

Entanglement entropy is a measure of the entanglement between two subsystems of a larger system. It is defined as the von Neumann entropy of one of the subsystems, which is a measure of its quantum uncertainty. Entanglement entropy quantifies the amount of information shared between two subsystems and can be used to study how quantum correlations between them evolve over time. Entanglement entropy can be used to study phenomena such as quantum phase transitions, topological order, and criticality.