Directional Coupling for Quantum Computing and Communication

We introduce the concept of directional coupling, i.e., the selective transfer of a state between adjacent quantum wires, in the context of quantum computing and communication. Our analysis rests upon a mathematical analogy between a dual-channel directional coupler and a composite spin system.

Figure 1

(a) A coupler consisting of six identical sites. (b) The coupler integrated in a dual-channel system.

Figure 2

Time evolution of an excitation in the QDC of Fig. 1b, with $N=7$. The excitation is transferred from the input port ($s,1$) to the output port of the drain channel ($d,N$) at $t=\tau$. The time is in units of ${\Omega }^{-1}$.