Recent progress for observation of ground-state two-proton decay

The ground-state two-proton decay is an exotic decay beyond proton drip line. It deals with the structure behavior of the proton pair at outside orbital in a proton drip-line nucleus, and can be used to check the current nuclear model under extreme condition. Experimental observation of ground-state two-proton decay has been widely considered as a challenge because of very low production cross section. In this short paper, the breakthrough of searching ground-state two-proton decay is briefly reviewed, which was made more than 40 years after the early theoretical prediction was proposed. (authors)