Illustration: Carin Cain

Figure 1: Experiments with ultracold molecules probe chemical reactions in a completely new, previously unattainable, temperature regime, where the translational energy of molecules is much smaller than the energy of hyperfine interactions and the de Broglie wavelength of molecules is much larger than the typical size of molecules. The scale above shows the de Broglie wavelength of $Cs2$ molecules in units of Bohr radius.