Tracking evaporative cooling of a mesoscopic atomic quantum gas in real time

TL;DR

This paper demonstrates real-time, minimally invasive tracking of atom number fluctuations in a mesoscopic quantum gas using an optical cavity, revealing insights into thermodynamics and transport phenomena.

Contribution

It introduces a continuous, non-destructive measurement technique for ultracold gases, enabling detailed study of fluctuations and correlations during evaporation.

Findings

Detected atom number fluctuations below Poissonian level

Characterized non-linearity in evaporation process

Measured two-time correlations of atom number

Abstract

The fluctuations in thermodynamic and transport properties in many-body systems gain importance as the number of constituent particles is reduced. Ultracold atomic gases provide a clean setting for the study of mesoscopic systems; however, the detection of temporal fluctuations is hindered by the typically destructive detection, precluding repeated precise measurements on the same sample. Here, we overcome this hindrance by utilizing the enhanced light--matter coupling in an optical cavity to perform a minimally invasive continuous measurement and track the time evolution of the atom number in a quasi two-dimensional atomic gas during evaporation from a tilted trapping potential. We demonstrate sufficient measurement precision to detect atom number fluctuations well below the level set by Poissonian statistics. Furthermore, we characterize the non-linearity of the evaporation process and the inherent fluctuations of the transport of atoms out of the trapping volume through two-time correlations of the atom number. Our results establish coupled atom--cavity systems as a novel testbed for observing thermodynamics and transport phenomena in mesosopic cold atomic gases and, generally, pave the way for measuring multi-time correlation functions of ultracold quantum gases.