Researchers from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), collaborating with researchers from Brookhaven National Laboratory, USA, and Shandong University, have achieved the first Fermi-scale single-particle double-slit experiment with an unstable particle ρ⁰ meson as the entity in a high-energy heavy-ion collision process. The study was published in Science Advances. 

Wave-particle duality is a cornerstone principle of quantum mechanics. The single-particle double-slit experiment is a direct phenomenological interpretation of wave-particle duality. Over the past 50 years, researchers have repeatedly carried out the experiment using photons, electrons, atoms, molecules, and biological macromolecules as interfering entities.  

Could the unstable particles commonly found in high-energy nuclear physics experiments also act as entities in a double-slit experiment? Researchers answered the question by utilizing gold nucleus-gold nucleus collisions.  

Both colliding nuclei could act as target nuclei, i.e., the "slits", for ρ⁰ meson scattering, resulting in interference. The process produced ρ⁰ mesons that were fully linearly polarized, and their decay products tended to move in the polarization direction, which resulted in a second-order cosine modulation of the decay angle that varied periodically with the magnitude of the ρ⁰ meson transverse momentum, the first manifestation of the double-slit interference phenomenon in polarization space.  

Interestingly, the typical distance between the two “slits” in these collisions was about 20 fm, much longer than the distance that can be reached before the ρ⁰ mesons decay, suggesting that the ρ⁰ meson wave functions from the two “slits” decayed before they met and overlapped, so that the ρ⁰ meson double-slit interference is produced by the concerted cooperation of its decay products (e.g., π⁺π^- pairs). These decaying π+π- pairs interfere in a "supertemporal" cooperative manner, providing an excellent model for interpreting the phenomenon of quantum entanglement.