  I present a four-party unlockable bound-entangled state, that is, a
four-party quantum state which cannot be written in a separable form and from
which no pure entanglement can be distilled by local quantum operations and
classical communication among the parties, and yet when any two of the parties
come together in the same laboratory they can perform a measurement which
enables the other two parties to create a pure maximally entangled state
between them without coming together. This unlocking ability can be viewed in
two ways, as either a determination of which Bell state is shared in the
mixture, or as a kind of quantum teleportation with cancellation of Pauli
operators.
