Abstract: On the centennial of quantum mechanics, the 2025 Nobel Prize in Physics was awarded to John Clarke, Michel H. Devoret, and John M. Martinis for their pioneering experiments on macroscopic quantum mechanical tunnelling and energy quantization. Although the scientific significance of this achievement has already prompted considerable discussions in both academic and public versions, a key question remains: given that macroscopic quantum phenomena (such as the superconducting Josephson effect and Bose-Einstein condensation) have been recognized by the Nobel committee on multiple occasions, why has the prize again honored work in a similar domain?
One of the present authors (C. P. Sun) conducted related research on quantum dissipation in macroscopic (mesoscopic) systems under the guidance of C. N. Yang in the early 1990s. Drawing on a survey of the prize-winning contributions and other historical literature, we offer a physically grounded interpretation of the award’s scientific significance: the laureates’work provided the first definitive experimental verification of the consequence of what may be termed third quantization (order-parameter quantization) —macroscopic quantum superposition—and can be viewed as the first experimental observation of Schrödinger-cat-state physics in macroscopic systems. Subsequently, the rapid development of superconducting quantum computing brought these advances to the public attention. It is also noteworthy that Chinese scholars (e. g., Y. Yu and J. Q. You) have made important contributions at various stages to extending the coherence times of macroscopic superconducting qubits.