Every year, the Royal Swedish Academy of Sciences celebrates outstanding discoveries in various fields of science, contributing to its development and popularization in society. In just a few years, advances in science and technology have allowed physicists to confirm the existence of black holes and gravitational waves, develop physical models of the Earth’s climate, and even discover distant exoplanets orbiting sun-like stars — each of which has won a Nobel Prize.
In 2022, Alain Aspect, John Clauser and Anton Zeilinger are the winners of the Nobel Prize in Physics. Three physicists have received the award for quantum entanglement experiments based on the work of such eminent scientists as Niels Bohr, Albert Einstein, and John Bell, all of whom wanted to understand the nature of the strange behavior of elementary particles that can be far apart while maintaining communication with each other.
Quantum entanglement – is a physical phenomenon in which the quantum states of two or more objects become interdependent. What happens to one particle in an entangled pair determines what happens to the other, even if they are too far away to influence each other. Its essence is that the measurement of any parameter of one particle is accompanied by instantaneous (faster than the speed of light) obtaining information about the state of another.
In recent decades, it has become clear that the phenomena of quantum mechanics, which seemed to have no practical use, associated with quantum entanglement, are nevertheless beginning to find application. At present, there is already a vast area of research, including quantum computers, quantum networks, and secure communication with quantum encryption, where they are used. It turned out that entangled quantum states have great potential for creating new ways of storing, transmitting and processing information. A major role in the development of this area of research was played by the work of the new Nobel laureates A. Aspect, J. Clauser and A. Zeilinger, who by their experiments not only solved a number of fundamental questions of the interpretation of quantum mechanics, but also opened the way for new technologies. The development of experimental instruments by the laureates laid the foundation for future quantum technologies. Each of them received a third of the Nobel Prize with the wording “For experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science“.
For a long time, the question remained open: is there some kind of hidden connection between entangled particles, imperceptibly from us telling them what result they should give in the experiment. Theoretically, this means the presence of hidden variables about which we know nothing. In the 1960s, J.S. Bell developed a mathematical inequality named after him. It argued that in the presence of latent variables, the correlation (characteristic of the relationship) between the results of a large number of measurements will never exceed a certain value. However, quantum mechanics predicted that a certain type of experiment could violate Bell’s inequality, which means there is a stronger correlation and, as a result, no hidden variables and connections.
The American physicist J. Clauser developed Bell’s ideas and conducted an experiment (1972) that clearly violated Bell’s inequality. This was the first experimental observation of a violation of Bell’s inequality. Clauser showed that quantum mechanics cannot be replaced by a theory using hidden variables. However, some questions still remain.
There were “vulnerabilities” in the theory whereby an opponent could question the results: what if the experimental setup somehow picked particles that were highly correlated and didn’t find others? If so, the particles may still carry hidden information. A French physicist, professor at the University of Paris-Saclay and the Polytechnic School, A. Aspect developed an installation that closed the most important loophole. To do this, he was able to come up with a mechanism for switching the measurement setting a few billionths of a second after the entangled pair left its source, so the setting that existed at the time of their emission could not affect the measurements. His experiment gave a very clear result: quantum mechanics is correct and there are no hidden variables.
The merit of the last of the awarded researchers, A. Zeilinger, is that he began to use entangled quantum states, using improved tools and a long series of experiments. Among other things, his research group has demonstrated a phenomenon called quantum teleportation, which allows a quantum state to be moved from one particle to another over a distance. This is the only way to transfer quantum information from one system to another without losing any part of it and an important part of future information technologies.
Compiled by: F. Shokir, A. Burkhonzoda, E. Okilov