Number Fluctuations of a Dipolar Condensate: Anisotropy and Slow Approach to the Thermodynamic Regime

TL;DR

This paper develops a theoretical framework to analyze number fluctuations in quasi-2D dipolar Bose-Einstein condensates, revealing anisotropic behavior due to dipole tilt and a slow approach to thermodynamic limits.

Contribution

It provides analytic results for quantum and thermal fluctuations in dipolar condensates, highlighting anisotropy and the slow convergence to thermodynamic behavior compared to short-range interactions.

Findings

Number fluctuations become anisotropic with dipole tilt.

Thermodynamic fluctuation limits are approached slowly with increasing cell size.

Experimental observation does not require high-resolution imaging.

Abstract

We present a theory for the number fluctuations of a quasi-two-dimensional (quasi-2D) dipolar Bose-Einstein condensate measured with finite resolution cells. We show that when the dipoles are tilted to have a component parallel to the plane of the trap, the number fluctuations become anisotropic, i.e. depend on the in-plane orientation of the measurement cell. We develop analytic results for the quantum and thermal fluctuations applicable to the cell sizes accessible in experiments. We show that as cell size is increased the thermodynamic fluctuation result is approached much more slowly than in condensates with short range interactions, so experiments would not require high numerical aperture imaging to observe the predicted effect.