Variance of an anisotropic Bose-Einstein condensate. (arXiv:1709.04223v1 [cond-mat.quant-gas])

The anisotropy of a trap potential can impact the density and variance of a
Bose-Einstein condensate (BEC) in an opposite manner. We exemplify this effect
for both the ground state and out-of-equilibrium dynamics of structureless
bosons interacting by a long-range inter-particle interaction and trapped in a
two-dimensional single-well potential. We demonstrate that even when the
density of the BEC is, say, wider along the $y$ direction and narrower along
the $x$ direction, its position variance can actually be smaller and momentum
variance larger in the $y$ direction than in the $x$ direction. This behavior
of the variance in a many-particle system is counterintuitive. It suggests
using the variance as a tool to characterize the strength of correlations along
the $y$ and $x$ directions in a trapped BEC.