Quantum entanglement as a quantifiable resource

Quantum mechanical objects can exhibit correlations with one another that are fundamentally at odds with the paradigm of classical physics; one says that the objects are ‘entangled’. In the last few years, entanglement has come to be studied not only as a marvel of nature but as a potential resource, particularly as a resource for certain unusual kinds of communication. This paper reviews two such uses of entanglement, called ‘teleportation’ and ‘dense coding’. Teleportation is the direct, though not instantaneous, transfer of a quantum state from one object to another over a distance. Dense coding is the effective doubling of the information–carrying capacity of a quantum particle through prior entanglement with a particle at the receiving end. The final section of the paper presents various quantitative measures of entanglement and considers novel features that arise when entanglement is shared among three objects.