Resonant-tunneling in discrete-time quantum walk

We show that discrete-time quantum walks on the line, $\mathbb{Z}$, behave as "the quantum tunneling". In particular, quantum walkers can tunnel through a double-well with the transmission probability $1$ under a mild condition. This is a property of quantum walks which cannot be seen on classical random walks, and is different from both linear spreadings and localizations.
Comment: 14 pages, 2 figures to appear in "Quantum Studies: Mathematics and Foundations"