  In 1961, Rolf Landauer pointed out that resetting a binary memory requires a
minimum energy of $k_BT \ln(2)$. However, once written, any memory is doomed to
loose its content if no action is taken. To avoid memory losses, a refresh
procedure is periodically performed. In this paper we present a theoretical
model and an experiment on a micro-electro-mechanical system to evaluate the
minimum energy required to preserve one bit of information over time. Two main
conclusions are drawn: i) in principle the energetic cost to preserve
information for a fixed time duration with a given error probability can be
arbitrarily reduced if the refresh procedure is performed often enough; ii) the
Heisenberg uncertainty principle sets an upper bound on the memory lifetime.
