S.C. was supported in part by the National Science Foundation through Grant No. PHY-1205931. L. Yu was supported by the National Research Foundation and Ministry of Education in Singapore. en_US dc.format.extent 5 pages
Physical Review A: Atomic, Molecular & Optical Physics
Linear algebra, Schmidt coefficients, Schmidt rank
We prove that every unitary acting on any multipartite system and having operator Schmidt rank equal to 2 can be diagonalized by local unitaries. This then implies that every such multipartite unitary is locally equivalent to a controlled unitary with every party but one controlling a set of unitaries on the last party. We also prove that any bipartite unitary of Schmidt rank 2 is locally equivalent to a controlled unitary where either party can be chosen as the control, and at least one party can control with two terms, which implies that each such unitary can be implemented using local operations and classical communication (LOCC) and a maximally entangled state on two qubits. These results hold regardless of the dimensions of the systems on which the unitary acts.
Cohen, S. M., & Li, Y. (2013). All unitaries having operator Schmidt rank 2 are controlled unitaries. Physical Review A: Atomic, Molecular & Optical Physics, 87(2-A), 022329-1-022329-6.