Verifying quantum entanglement

Science: Quantum mechanical systems may exhibit correlations between their parts that are stronger than those permitted by classical physics. These correlations have challenged our understanding of the concepts of locality and reality in quantum mechanics (1). It was the crucial insight that entanglement actually represents a resource that has led to the rapid development of modern quantum information science, in which entanglement is used to realize novel information processing tasks. Unfortunately, the current experimental realizations are still imperfect and noisy. For the development of practical quantum technologies, it is therefore necessary to be able to verify quantitatively the presence of entanglement, as well as the quality of that entanglement and of the quantum information processors. Recent advances toward this goal have been made.