Accurate temperature measurement of cold atoms in cesium fountain clocks

We introduce a new approach to determine if a cloud of cold atoms has or not a unique, well-defined temperature. In the first case, the temperature can be determined using the width of the velocity distribution. However, the temperature in a cloud of cold atoms may not be well-defined if the velocity distribution does not turn out to be Gaussian. In this case, the width of the velocity distribution cannot be associated to a unique temperature, and additional considerations exposed here should be followed to measure the temperatures of two groups of atoms forming the whole cloud. Also an uncertainty evaluation is presented. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement