Implementation of Atom-Counting in the BEC-Experiment


The observation of many quantum effects in a spinor Bose gas rely on the possibility for detection at the single-atom level. In a dedicated setup in our group it has been shown that fluorescence imaging is capable of achieving single-atom resolution even for mesoscopic atom numbers of up to 1200 atoms [1]. For that the atoms are trapped in a magneto-optical trap (MOT) and the fluorescence signal is recorded. By reducing mainly the background and fluorescence noise the signal can be resolved at the single-atom level. We realised this in the BEC-experiment by using four small fibre-coupled laser beams together with two bigger ones from the usual experimental setup to produce a MOT. Additionally, we built an intensity stabilisation system with LCD-shutter glasses for the fibre-coupled beams. We observed the fluorescence signal with single-atom resolution for more than twenty atoms in the sample and analysed the signal with respect to the different noise contributions. With these values we can calculate the fidelity of this detector, i.e. the probability to have detected the right atom number. In the end, ways to improve the detection system are proposed and the possibility to already use this system to measure the atomic Hong-Ou-Mandel effect is discussed.