  We describe a simple experimental technique which allows to store a single
Rubidium 87 atom in an optical dipole trap. Due to light-induced two-body
collisions during the loading stage of the trap the maximum number of captured
atoms is locked to one. This collisional blockade effect is confirmed by the
observation of photon anti-bunching in the detected fluorescence light. The
spectral properties of single photons emitted by the atom were studied with a
narrow-band scanning cavity. We find that the atomic fluorescence spectrum is
dominated by the spectral width of the exciting laser light field. In addition
we observe a spectral broadening of the atomic fluorescence light due to the
Doppler effect. This allows us to determine the mean kinetic energy of the
trapped atom corresponding to a temperature of 105 micro Kelvin. This simple
single-atom trap is the key element for the generation of atom-photon
entanglement required for future applications in quantum communication and a
first loophole-free test of Bell's inequality.
