Mesoscopic Atom Number Detection and Cold Atom Dynamics

吀�e ability to manipulate cold atoms has been constantly improved over the past three decades in an endeavour to achieve the best control and the best detection of these particles. Atom-light interaction has proven fundamental for the cooling and trapping of neutral atoms and several detection techniques have been developed, including absorption and fluorescence imaging. Here we present a detection technique based on fluorescence imaging, which is able to reach the ultimate limit of single-atom resolution for mesoscopic samples of up to 1200 particles. In order to render the detection sensitive to multiple hyperfine states of the atomic system, we developed a novel hybrid trap in form of a dissipative double-well potential. 吀�is allows the accurate determination of the difference in the hyperfine state population for samples with up to 500 particles. Furthermore, by varying the potential barrier height between the two sites of the double-well, with this unique system it is possible to measure hopping rates over five orders of magnitude. We confirmArrhenius’ law for small barriers and find that particle exchange induced by light-assisted collisions dominates the dynamics for large barriers. Finally, we observe the stochastic resonance effect, in which a weak external driving of the double-well system is amplified by the addition of thermal noise