Spontaneous　symmetry　breaking　(SSB)　plays　a　central　role　in　understanding　a　large　variety　of　phenomena　associated　with　phase　transitions,　such　as　superfluid　and　superconductivity.　So　far,　the　transition　from　a　symmetric　vacuum　to　a　macroscopically　ordered　phase　has　been　substantially　explored.　The　process　bridging　these　two　distinct　phases　is　critical　to　understanding　how　a　classical　world　emerges　from　a　quantum　phase　transition,　but　so　far　remains　unexplored　in　experiment.　We　here　report　an　experimental　demonstration　of　such　a　process　with　a　quantum　Rabi　model　engineered　with　a　superconducting　circuit.　We　move　the　system　from　the　normal　phase　to　the　superradiant　phase　featuring　two　symmetry-breaking　field　components,　one　of　which　is　observed　to　emerge　as　the　classical　reality.　The　results　demonstrate　that　the　environment-induced　decoherence　plays　a　critical　role　in　the　SSB.　©　2024,　Science　China　Press.