Efficient fluorescence detection of a single neutral atom with low background in a microscopic optical dipole trap

A single cesium atom is trapped in a far-off-resonance optical dipole trap (FORT) from the magneto-optical trap (MOT) and directly imaged by using a charge-coupled device (CCD) camera. The binary single-atom steps and photon anti-bunching are observed by a photon-counting-based HBT system using fluorescence light. The average atom dwelling time in the FORT is about 9 s. To reduce the background noise in the detection procedure we employ a weak probe laser tuned to the D1 line to illuminate the single atom from the direction perpendicular to the large-numerical-aperture collimation system. The second order degree of coherence g(2)(τ)=0.12±0.02 is obtained directly from the fluorescence light of the single atom without deducting the background. The background light has been suppressed to 10 counts per 50 ms, which is much lower compared with the reported results. The measured g(2)(τ) is in good agreement with theoretical analysis. The system provides a simple and efficient method to manipulate and measure single neutral atoms, and opens a way to create an efficient controlled single-photon source.