Abstract:

Quantum systems are typically characterized by the inherent fluctuation of their physical properties. The size of these fluctuations is particularly relevant for the case of interacting Bose gases at the transition to Bose-Einstein condensation. Despite its importance this case has resisted a consistent experimental and theoretical investigation for decades. We have characterized these fluctuations in an experimentally accessible range of aspect ratios, temperatures and atom numbers. Strikingly, we observe fluctuations reduced by 27% below the canonical expectation for a non-interacting gas, revealing the microcanonical nature of our system. Moreover, we explore the scaling of these fluctuation with atom number providing an exponent of 1.134 in a region outside the thermodynamic limit. Our experimental results thus set a benchmark for further theoretical calculations under experimental conditions.