Measurement of the temperature of atomic ensembles via which-way information

We unveil the relationship existing between the temperature of an atomic ensemble of three-level atoms in a \Lambda-configuration, and the width of the emission cone of Stokes photons that are spontaneously emitted when atoms are excited by an optical beam. This relationship, which is based on the amount of which-way information available about where the Stokes photon originated during the interaction, allow us to put forward a scheme to determine the temperature of atomic clouds by measuring the width of the emission cone. Unlike the commonly used time-of-flight measurements, with this technique, the atomic cloud is not destroyed during each measurement.