Emmanuel Zambrini Cruzeiro, a professor at Técnico and researcher at Instituto de Telecomunicações (IT), and Paulo Freitas, a professor at Técnico and researcher atm Instituto de Engenharia de Sistemas e Computadores – Microsistemas e Nanotecnologias (INESC-MN), share their views on the Nobel Prize in Physics 2025 awarded to John Clarke, Michel H. Devoret and John M. Martinis for the discovery of macroscopic quantum mechanical tunnelling.
How would you explain the importance of the work recognised by the Nobel Prize in Physics 2025? How does it justify the Nobel Prize?
Emmanuel Zambrini Cruzeiro (EZC) – Quantum physics is a fascinating field because it provides surprisingly accurate explanations for the often counterintuitive world of particles and atoms at a microscopic level. In other words, it offers us a relatively simple “mathematical recipe book” for predicting the results of experiments on a microscopic scale. However, there is nothing in the theory that implies that it does not apply to larger scales. One of the biggest fundamental questions in physics is whether quantum physics applies to larger objects, or if there are any limitations. So far, quantum physics has defied all our attempts to contradict it experimentally. If we find a limitation related to the size of a system, it could lead us towards the next significant theory of nature. This year’s Nobel Prize honours the work of three physicists who demonstrated that the quantum tunnelling effect occurs in currents made up of millions of electrons. In this sense, the current can be seen as macroscopic, and therefore the prize was awarded for the demonstration of the quantum tunnelling effect at the macroscopic level.
Paulo Freitas (PF) – The award-winning work provides the first experimental evidence of a macroscopic quantum tunnelling effect. The three physicists who won the Nobel Prize worked on integrated superconducting circuits (on a chip) containing Josephson junctions – a tunnel junction between two superconductors separated by a thin insulating barrier (measuring 1 to 2 nm). They found that these circuits exhibit quantised macroscopic behaviour, allowing them to be treated as particles that can exhibit quantum behaviour (non-zero probability of crossing a barrier). The state of these circuits can be altered using microwaves or by applying a voltage to the junction.
What scientific advances have resulted from the work of these researchers? What benefits could they bring in the future?
PF – Work on superconducting circuits began in the 1980s with a view to reducing energy consumption and increasing processing speed in supercomputers. This initial work led to the development of SQUIDS (superconducting quantum interference devices) as precision magnetometers, for example, in magnetoencephalography. Other applications in ultra-fast electronics use superconducting circuits. Additionally, superconducting qubits (quantum bits) are central to most of the quantum computer prototypes currently being developed, and their work has significant implications in this field.
EZC – The results obtained by the honoured scientists were crucial in developing components for quantum computing, particularly those involving Josephson junctions. These devices allow a current with many particles to flow through a superconducting material, exhibiting quantum properties. This allows for the creation of a unit of information known as a quantum bit (QUBIT). In this context, a superconducting quantum bit can exist in a superposition of states (e.g., both on and off simultaneously). More significantly, these developments have confirmed that quantum physics can be validated in relatively large systems, involving around a million electrons. Continuing this line of research promises even more benefits; for example, quantum effects have now been observed in molecules, paving the way for new technologies.
What other advances in physics would you like to have seen recognized with the Nobel Prize this year?
EZC – There are several possibilities. I was pleased to see that this year’s prize is associated with quantum physics and quantum technologies, but other advances in these areas also deserve attention. One fascinating example is the emerging technologies for detecting single photons, which will revolutionise various fields of science. Other fields of physics that could have been considered include cosmology, condensed matter, and fusion, in which there has also been much progress.
PF – Recent advances in topological materials, new functional heterostructures, development of quantum sensors.
How does your work relate to that of the award winners?
Since 1997, INESC-MN has been studying spin tunnel junctions—a quantum device where electrons cross a crystalline or amorphous insulating barrier through quantum tunneling. The transmission coefficient in these junctions is influenced by the spin polarization on each side of the barrier, as well as the orientation of the magnetisation on each side of the barrier (magnetic electrodes). This concept, initially proposed by Julliere (in the 1980s), is now used in various devices, from non-volatile magnetic random-access memories (MRAM) and hard disk read heads to a variety of magnetic sensors (field sensors, integrated compasses, current sensors, angular and linear sensors, and others).
EZC – At IT/Técnico, one of the main lines of research of our group studies quantum phenomena on a macroscopic scale. More specifically, we study quantum correlations and how to identify them in macroscopic systems. Currently, quantum properties have been demonstrated with well over a million particles. To advance further, it is essential to develop both experimental and theoretical tools, making this area of research even more thrilling.
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