Kavan Modi, University of Oxford
Abstract
We give a concrete meaning to quantum discord by discussing some new tasks for which quantum discord is a resource. First: How can Alice test Bob's claim that he possesses a quantum computer? We give a protocol that tests Bob's ability to coherently interact two qubits. Alice encodes a message on one of two qubits qubit and challenges Bob to decode the message. The amount of information that Bob can gain via quantum means over classical means equal quantum discord consumed during Alice's encoding. Second: Two distant labs cannot increase the entanglement between them via classical communication. However, they can do so via quantum communication. Surprisingly, the communicated system need not be entangled with either / both of the labs, but it must be quantum correlated (as determined by quantum discord. and discord that bounds the increase in the entanglement. Additionally, the bound also leads to subadditivity of entropy and gives an interpretation for negative conditional entropy.