TURBULENCE AND SUPERFLUIDITY IN THE ATOMIC BOSE-EINSTEIN CONDENSATE

Abstract

In this dissertation I investigate turbulence in atomic Bose-Einstein condensates (BECs), focusing on the challenge of quantifying velocity field measurements in quantum fluids. Turbulence, a universal phenomenon observed across various scales and mediums – from classical systems like Earth's oceans and atmosphere to quantum fluids including neutron stars, superfluid helium, and atomic BECs – exhibits complex fluid motion patterns spanning a wide range of length scales. While classical turbulence has been extensively studied, quantum systems present many open questions, particularly regarding the existence of an inertial scale and the applicability of Kolmogorov scaling laws.

I introduce a novel velocimetry technique, analogous to particle image velocimetry (PIV), using spinor impurities as tracer particles. This method enables the direct measurement of the velocity field and thereby the velocity structure functions (VSFs) in turbulent atomic BECs. The technique overcomes limitations of existing experimental approaches that rely on time of flight (TOF) measurements, offering a clearer connection to VSFs and enabling a more direct comparison of turbulence in atomic gases with other fluids.

The cold-atom PIV technique enables directly measuring the velocity field, leading to a detailed analysis of both VSFs and the velocity increment probability density functions (VI-PDF). Key findings include the observation of superfluid turbulence conforming to Kolmogorov theory from VSFs, and intermittency from high order of VSFs and the non-Gaussian fat tail in the VI-PDF.