We propose to use adiabatic rapid passage with a chirped laser pulse in the
strong dipole blockade regime to deterministically excite only one Rydberg atom
from randomly loaded optical dipole traps or optical lattices. The chirped
laser excitation is shown to be insensitive to the random number \textit{N} of
the atoms in the traps. Our method overcomes the problem of the N​
dependence of the collective Rabi frequency, which was the main obstacle for
deterministic single-atom excitation in the ensembles with unknown \textit{N},
and can be applied for single-atom loading of dipole traps and optical
lattices.Comment: 6 pages, 5 figures. Version 5 is expanded and submitted to PRA. Typo
in Fig.4 corrected in Version 2. Version 3 and 4 are duplicates of V