Prof. Dr. Rok Žitko (IJS, FMF): Nobel Prize in Physics 2025

The 2025 Nobel Prize in Physics has been awarded to John Clarke, Michel Devoret and John Martinis for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit. Prior to their experiments, quantum mechanics was only known to survive at the macroscopic scale through collective phenomena such as superfluidity and superconductivity, arising from the coherent addition of microscopic degrees of freedom. In macroscopic quantum tunnelling in a Josephson circuit, a single macroscopic degree of freedom exhibits quantum behaviour. The awardees managed to determine all the relevant parameters of the device in situ in the classical regime, enabling a comparison of their experimental results with the theory of dissipative quantum systems with no fitted parameters, thereby providing conclusive evidence. Their work marks the beginning of superconducting quantum electronics that enabled further foundational experiments and the development of quantum processors.
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