  We analyze the effects of the temperature on a bosonic Josephson junction
realized with ultracold and dilute atoms in a double-well potential. Starting
from the eigenstates of the two-site Bose-Hubbard Hamiltonian, we calculate the
coherence visibility and the fluctuation of the on-site occupation number and
study them as functions of the temperature. We show that, contrary to naive
expectations, when the boson-boson interaction is suitably chosen thermal
effects can increase the coherence visibility and reduce the on-site number
fluctuation.
