## Direct observation of quantum phonon fluctuations in a one dimensional Bose gas    [PDF]

Julien Armijo
We report direct observation of collective quantum fluctuations of the
density in ultracold atomic 1D clouds with weak repulsive interactions.
Shot-to-shot atom number fluctuations in small gas sub-volumes are studied
using \textit{in situ} absorption imaging and statistical analysis of the
density profiles. In the cloud centers, well in the quantum quasicondensate
regime, the ratio of chemical potential to thermal energy is $\mu/ k_B T\simeq4$, and, owing to high resolution, up to 20% of the microscopically
observed fluctuations are quantum phonons. Moreover, varying the observation
length, we observe a clear deviation from a classical field prediction, which
reveals the emergence of dominant quantum fluctuations at short observation
lengths, as the thermodynamic limit breaks down.
View original: http://arxiv.org/abs/1112.4199