Enhanced and Reduced Atom Number Fluctuations in a BEC Splitter

We measure atom number statistics after splitting a gas of ultracold Rb87 atoms in a purely magnetic double-well potential created on an atom chip. Well below the critical temperature for Bose-Einstein condensation Tc, we observe reduced fluctuations down to −4.9  dB below the atom shot noise level. Fluctuations rise to more than +3.8  dB close to Tc, before reaching the shot noise level for higher temperatures. We use two-mode and classical field simulations to model these results. This allows us to confirm that the supershot noise fluctuations directly originate from quantum statistics.