  We introduce a tight-binding chain with a single impurity to act as a quantum
data bus for perfect quantum state transfer. Our proposal is based on the weak
coupling limit of the two outermost quantum dots to the data bus. First show
that the data bus has an energy gap between the ground and first-excited states
in the single-particle case induced by the impurity in the single particle
case. By connecting two quantum dots to two sites of the data bus, the system
can accomplish a high-fidelity and long-distance quantum state transfer.
Numerical simulations were performed for a finite system; the results show that
the numerical and analytical results of the effective coupling strength agree
well with each other. Moreover, we study the robustness of this quantum
communication protocol in the presence of disorder in the couplings between the
nearest-neighbor quantum dots. We find that the gap of the system plays an
important role in robust quantum state transfer.
