Is it possible to create a Schrödinger’s cat in a laboratory - that is, to make a macroscopic object obey the laws of quantum mechanics? The 2025 Nobel Prize in Physics recognizes experiments showing that this is indeed possible, using superconducting electrical circuits.
The 2025 Nobel Prize in Physics recognizes a conceptual shift that has been more than a century in the making: the transition from observing quantum phenomena in materials to deliberately engineering quantum behaviour in macroscopic electrical circuits. Awarded to John Clarke, Michel Devoret, and John Martinis, the prize honours the experimental demonstration and control of macroscopic quantum tunnelling and energy quantization in superconducting circuits. Their work resolved a long-standing question at the heart of quantum mechanics: can an object large enough to wire, probe, and manipulate behave as a single quantum system? The answer, now unequivocally, is yes.
In this paper I first briefly review the apparently bizarre consequences of attempting to apply quantum mechanics consistently to macroscopic bodies in certain kinds of situations (the ‘Schrödinger's Cat’ paradox). The paradox results from the assumption that the linear superpositions of macroscopically distinct states, which are unambiguously predicted by the formalism, do indeed exist in nature. Until recently, this assumption was experimentally untested. However, recent advances in techniques of microfabrication, cryogenics and noise control have opened up the possibility of indirect and possibly even direct tests, in particular in superconducting systems incorporating Josephson devices. I describe some of these tests, review the current experimental and theoretical situation and discuss the implications of various possible outcomes to the experiments.
It is widely believed that the microscopic, that is, atomic-scale or smaller, world is governed by quantum mechanics while the macroscopic world, where our direct and daily experiences reside, is governed by classical mechanics. But why? Why do we not observe quantum phenomena such as quantum tunneling and quantum superposition in the macroscopic world? Where is the boundary between the microscopic and macroscopic worlds when it comes to the governing physical principles? Macroscopic quantum phenomena were first examined theoretically by A. Leggett in the 1970s. This boldly audacious idea was experimentally demonstrated in a series of groundbreaking works on Josephson junctions by John Clarke, Michel Devoret, and John Martinis in 1985, that have been celebrated by the 2025 Nobel Prize in Physics. The trio’s work spurred the development of various qubit types based on superconducting circuits, ultimately leading to the current advancement of superconducting quantum computers.
Superconducting quantum circuits have reached impressive performance, with individual qubits and operations working extremely well. This maturity was recognized by the 2025 Nobel Prize in Physics, awarded for demonstrating that genuinely quantum phenomena – such as energy quantization and tunnelling – can occur in macroscopic electrical circuits. Yet building large, reliable quantum processors remains challenging. The limitation is no longer a single flaw, but the combined effect of many small imperfections spread across the hardware. Subtle losses in materials, tiny variations in components, unwanted heat, and constraints imposed by wiring, packaging, and control electronics all accumulate as systems grow in size. This article explains how such device-level effects ultimately limit the performance of entire quantum processors, and why understanding this link is essential for turning today’s high-quality quantum devices into scalable and reliable quantum technologies.
The Nobel laureates of this year have devised an experiment to observe macroscopic quantum tunneling in an electrical circuit made of superconductors. This monumental discovery has sparked numerous innovations and ultimately earned the three pioneers the Nobel prize. Afterwards, superconducting circuits play a key role in the proliferation of quantum technology in the 21st century. Especially, in the heart of the 2nd quantum revolution, quantum information technology is based on the radical development of the quantum computers. Superconducting Josephson junction devices has been the most advanced technology that has been picked up by the global tech giants in quantum computing. I will briefly review how the superconducting quantum chips and the macroscopic quantum effect had led innovation in quantum technology afterwards.
The Nobel Prize in Physics 2025 was awarded jointly to John Clarke,Michel H. Devoret and John M. Martinis “for the discovery of macroscopic quantum mechanical tunnelling and energy quantization in an electric circuit”. Their landmark research validated the laws of quantum mechanics at the macroscopic scale,breaking the traditional notion that quantum behavior is confined to the microscopic realm. This breakthrough directly catalyzed the advent of superconducting quantum computing and has been hailed as “opening a door to quantum technologies.”