State redistribution as merging: introducing the coherent relay

Understand

State redistribution allows one party to optimally send part of her state to another party.

• Here we show that this can be derived simply from two applications of coherent state-merging.
• This provides a protocol whereby a middle party acts as a relay station to help another party more efficiently transfer quantum states.
• This also gives a protocol for state splitting and the reverse Shannon theorem (assisted or unassisted by side information), and allows one to use less classical communication for partial state-merging using a sub-protocol we call ebit repackaging.