Power of Entanglement in Quantum Communication

A communication channel is a physical system that transfers information from one place to another. Examples of communication channels include wires, optical fibers, and chains of spins that propagate spin waves through a medium. This Letter shows that the power-limited communication capacity of a multimode optical fiber or a set of parallel spin chains can be enhanced by introducing nonlinear couplings between the modes or chains. In particular, $M$ coupled, entangled modes can send $M$ bits in the same time it takes a single mode to send a single bit, and in the same time it takes $M$ uncoupled, unentangled modes to send $\sqrt{M}$ bits.