Quantum statistical effect on ionizing collisions of ultracold metastable Kr isotopes

Ultracold ionizing collisions of laser-cooled Kr isotopes in the 1${\mathit{s}}_5$[4${\mathit{p}}^5$5s${:}^3$ ${\mathit{P}}_2$] metastable state are investigated. When the collision energy is reduced below the p-wave centrifugal barrier of 80 μK, the ratio of the ionizing collision rate between polarized and unpolarized ${}_{}{}^{83}{}_{}{}^{}\mathrm{Kr}$ atoms is found to decrease. This is a direct evidence of the quantum interference of two identical Fermi particles. The experimental results are compared with the calculation based on the simplified inelastic collision theory.