Nobel Prize in Physics Awarded for Quantum Tunnelling: ITMO NEWS Explains

“The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics 2025 to John Clarke, Michel H. Devoret, and John M. Martinis for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit,” states a press release from the Nobel Committee. 

At the quantum level, particles are so small that specific quantum effects start to manifest. One of them is quantum tunnelling: this is when a particle can surpass an energy barrier even if its own energy is less than that of the barrier. For instance, in the macro world, if you throw a ball at the wall, the laws of classical physics state that the ball will bounce off it; in the micro world, ruled by the laws of quantum physics, there is a chance that the ball will pass through the wall.

Previously, it was believed that quantum tunneling only occurs at the microscopic scale in certain atoms and electrons. However, there were theoretical predictions that quantum mechanical effects could manifest in a macroscopic system consisting of a million separate particles; for instance, in an electron gas in a superconductive state.

The scientists confirmed their hypotheses in a series of experiments in 1984-1985 – a feat that earned them this Nobel Prize. John Clarke, Michel Devoret, and John Martinis had created an electronic chain of superconductors, components that can conduct electricity without resistance. These superconducting parts were separated by the so-called Josephson transistor – a thin isolating layer. The charged particles moving along the superconductor presented a unified system and resembled a single particle. According to the laws of classical physics, this particle shouldn’t have been able to pass through the isolating layer, but it acted within the laws of quantum physics and was able to go from a state with no resistance to a state with resistance. At the same time, the particle absorbed and radiated only a limited amount of energy, as per laws of quantum mechanics.

“As they transition to the superconducting state, all electrons in the material synchronize and can be described by the Ginzburg-Landau equation. By the way, Vitaly Ginzburg was awarded the Nobel Prize in Physics in 2003 for that very equation. John Clarke, Michel Devoret, and John Martinis in their turn wanted to know if it is possible for a macroscopic superconductor to exhibit the same behavior as a single microscopic quantum particle. The researchers demonstrated a tunnelling effect, wherein a microscopic quantum particle can with a non-zero probability “pass” through a wall – but with a macroscopic cloud of a billion electrons in the superconducting state. Moreover, the experiment demonstrated that the cloud of electrons in a semiconductor can have only discrete energy levels. These energy levels are actively used in modern superconductor-based quantum computers that are developed abroad and in Russia – for instance, at the Russian Quantum Center, Bauman Moscow State Technical University, and National University of Science and Technology ‘MISIS’,” explains Ivan Iorsh.

As noted by the Nobel Committee, the discovery is already used in transistors in computer microchips and has provided opportunities for development of the next generation of quantum technologies, including quantum cryptography, quantum computers, and quantum sensors.

At ITMO, new quantum materials are synthesized and studied by the research group of Vasily Kravtsov, a leading researcher at the School of Physics and Engineering. In one of their projects, the team applied a synthesized 2D material to create single photon emitters for use in quantum cryptography and quantum sensors. The researchers have also developed a device that can bind and control particles of light and matter; it can be used as a foundation for faster computer architecture, transmitters, and internet networks. Another project completed by the team is a supethin light-emitting component for ultra-thin screens.