We propose a scheme for perfect transfer of an unknown qubit state via the
discrete-time quantum walk on a line or a circle. For this purpose, we
introduce an additional coin operator which is applied at the end of the walk.
This operator does not depend on the state to be transferred. We show that
perfect state transfer over an arbitrary distance can be achieved only if the
walk is driven by an identity or a flip coin operator. Other biased coin
operators and Hadamard coin allow perfect state transfer over finite distances
only. Furthermore, we show that quantum walks ending with a perfect state
transfer are periodic.Comment: 13 pages, 5 figure
