the supernova simulations without incorporating fluid instabilities may fail to explode (see, e.g., the report by Wilson & Mayle[@wm93]). Generally, the simulations based on this mechanism give too low an energy, e.g. 0.3-0.4 foe (1 foe $=10^{51}$ ergs), to meet the observed energy of SN 1987A (at least 1.0 foe). Recent two-dimensional simulations by Mezzacapa et al.[@mez98] showed that the neutrino-driven convection is not adequate to give an “optimistic” 15$M_\odot$ supernova model, and the simulated timescale for explosion is longer than what is observed. Furthermore, these authors pointed out that more realistic three-dimensional simulation may be more, not less, difficult to obtain a successful explosion.

Therefore, the key criterion for a successful explosion [*and*]{} its large enough energy should be the sufficient neutrino energy deposition behind the stalled shock. One possible way to enhance neutrino luminosity is through phase transitions, such as the transition from nuclear matter to two-flavor quark matter and from two-flavor quark matter to strange quark matter (SQM)[@gen93dpl95aggs97]. After the core bounce, the central temperature and density of a proto-neutron star with a typical radius $\sim 50~$km[@bl86] might be high enough to induce a QCD phase transition. A strange star will be finally formed if SQM is 