The Nobel Prize in Physics goes to researchers who discovered "quantum mechanics in action" inside a chip.
Researchers John Clarke, Michel H. Devoret, and John M. Martinis identified "macroscopic quantum mechanical tunneling"
It couldn't be the year of quantum mechanics without the Nobel Prize in Physics also being awarded to the progress made in this field of physics over the last hundred years. Thus, the Swedish Academy of Sciences has awarded the prize to John Clarke, Michel H. Devoret, and John M. Martinis of the University of California, for their discovery of the macroscopic quantum tunneling effect and the quantization of energy in an electrical circuit. "It's fantastic to be able to celebrate that quantum mechanics has yielded many surprises in its hundred years of existence and is the basis of our technology," remarked Olle Eriksson, a member of the Nobel Prize Committee in Physics.
The question scientists studied in 1985 was to what extent quantum phenomena are still present. The studies carried out by scientists at the University of California were key in laying the foundations for the electronics found today in mobile phones and computers. Moreover, they have also led to advances that are fundamental in the development of quantum computers today. "We never imagined the implications our research would have," Clarke said after learning of the award. Her experiments revealed "quantum mechanics in action"—that is, they demonstrated that the properties of quantum mechanics can be realized on a macroscopic scale.
Breaking Through Insurmountable Walls
Almost a hundred years ago, Austrian physicist Erwin Schrödinger developed the foundations of quantum mechanics, a theory that explains how the microscopic world works. According to this theory, subatomic particles could cross barriers that, according to classical theory, would be impossible to cross. We can imagine a girl kicking a ball against a solid wall. In one of those shots against the wall, the ball doesn't bounce and ends up on the other side without leaving any trace. This is a phenomenon that, despite not making sense in the classical world we are used to, is quite common in the microscopic world.
However, as the number of particles involved increases, quantum effects like this become insignificant. The transition between the quantum world and the macroscopic scale has been, since its foundation, one of the fundamental questions of quantum mechanics. The experiments carried out by the Nobel laureates demonstrated that these quantum effects can not only be observed on macroscopic scales but also have a wide range of applications.
Perfectly orchestrated particles within a chip
In an ordinary conductor, current flows because there is a voltage and electrons circulating freely through the material. In some special materials, individual electrons are arranged in pairs, known as Cooper pairs. In this state, the particles move synchronously through the material without electrical resistance. This quantum state in which the material exists is known as a superconductor.
Between 1984 and 1985, Clarke, Devoret, and Martinis conducted a series of experiments with a chip composed of superconductors. In this electrical circuit, the conductors were separated by a thin layer of insulating material called a Josephson junction. When they measured the properties of this circuit, they realized they could explore quantum phenomena in a controlled manner when they passed current through it. The three researchers observed that the charged particles moved through the superconductor as if they were a single particle, occupying the entire circuit. This macroparticle is in a state in which electric current flows without the need for any applied voltage. Experiments demonstrated the quantum nature of this macrostate by showing that it was capable of transitioning to another state through quantum tunneling. "We spent over a year working on this experiment. The collaboration with Devoret and Martinis was essential," explained Clarke, who led the experiment.
The basis of today's technology
The transistors that make up the microchips in our computers or mobile phones are the most notable examples in which quantum mechanics has been shown to play an important role in our daily lives. The developments derived from the research of Clarke, Devoret and Martinis have opened the door to a new generation of quantum technologies, including quantum cryptography, and quantum computers and sensors. Currently, Catalonia is a leading center in the development of this new technological generation, known as the second quantum revolution, with the research carried out at the Institute of Photonic Sciences (ICFO) and with emerging companies such as LuxQuanta or Qilimanjaro.
The quantum computing expert at the Barcelona Supercomputing Center and coordinator of Quantum Spain, Alba Cervera, has highlighted that the award follows the line of the 2022 Nobel Prize in Physics, in which the pioneers of quantum information Alain Aspect, John Clauser, and Anton Zeilinger. "This award recognizes the development of the physics necessary to exploit quantum information to manufacture technology. Many current quantum computers are built with superconducting qubits, that is, using the principles developed by this year's winners," Cervera explained in a statement to the Science Media Centre.
