  Entanglement is one of the essential resources in quantum information and
communication technology (QICT). The entanglement thus far explored and applied
to QICT has been pure and distillable entanglement. Yet there is another type
of entanglement, called 'bound entanglement', which is not distillable by local
operations and classical communication (LOCC). We demonstrate the experimental
'activation' of the bound entanglement held in the four-qubit Smolin state,
unleashing its immanent entanglement in distillable form, with the help of
auxiliary two-qubit entanglement and LOCC. We anticipate that it opens the way
to a new class of QICT applications that utilize more general classes of
entanglement than ever, including bound entanglement.

Quantum Physics