Quantum Institute: Visitor Schedule

The Quantum Lunch is regularly held on Thursdays in the Theoretical Division Conference Room, TA-3, Building 123, Room 121. For more information, contact Diego Dalvit.

February 20, 2007
Monday, 12:30 PM

Jon Yard,
Caltech

Redistributing Quantum States

Abstract

Consider a pure quantum state with four parts and assume that Alice holds two of them while Bob holds one. The last is considered as an inaccessible "reference" system. For the situation where many copies of the same state are present, I will characterize the asymptotic resources which are necessary and sufficient for Alice to give one of her parts to Bob, while preserving the purity of the global state. For this, we allow Alice to send qubits to Bob; they may also use preexisting entanglement. The required qubit cost gives the first known operational interpretation of quantum conditional mutual information on an arbitrary underlying state. The optimal entanglement cost can be positive or negative, where in the latter case, entanglement is generated by the process. Some intuitively satisfying properties of our result include a time-reversal symmetry, together with a successive refinability property which is absent in the classical theory. I will then show how this result organizes and generalizes a large body of quantum information-theoretic results of recent years, such the quantum reverse Shannon and fully quantum Slepian-Wolf theorems. I will conclude with some words on the quantum method of types and some indications of future research directions.