  The equation $- \Delta u + V u = 0$ in the cylinder $\mathbb{R} \times
(0,2\pi)^d$ with periodic boundary conditions is considered. The potential $V$
is assumed to be bounded, and both functions $u$ and $V$ are assumed to be
real-valued. It is shown that the fastest rate of decay at infinity of
non-trivial solution $u$ is $O\left(e^{-c|w|}\right)$ for $d=1$ or $2$, and
$O\left(e^{-c|w|^{4/3}}\right)$ for $d\ge 3$. Here $w$ is the axial variable.
