Researchers from Tel Aviv University have shown how it will be possible to demonstrate the behavior of a large object, which contradicts Newton's classical physics

Until now, it was customary to differentiate between quantum theory, which affects small objects at small distances, and classical physics, which affects large bodies at large distances

Researchers from Tel Aviv University, led by Prof. Ron Lifshitz, showed how it would be possible to demonstrate the behavior of a large object, which contradicts Newton's classical physics. This is by slight improvements in the existing technology. In their study published these days in the scientific journal Physical Review Letters, the researchers show that clear measurable differences are expected, which will allow physicists in the laboratory to decide once and for all the issue of the quantum behavior of large objects. The study, which was funded by the Israel-USA Binational Research Fund (BSF), and funded by the Ministry of Science, was carried out by Itamar Katz as part of his master's thesis in physics under the guidance of Prof. Ron Lifshitz from the School of Physics and Astronomy. Alex Retzker, currently a post-doctoral researcher at Imperial College in London, and Raphael Straub, who stayed at Tel Aviv University as part of a student exchange program with the University of Konstanz in Germany, also participated in the study.

More than seventy years ago, one of the fathers of quantum theory, Erwin Schrödinger, described a paradox in which a cat is in a closed room in a kind of combined state (superposition in the language of physics) where it is both alive and dead. The cat can remain like this between life and death, as it were experiencing both of these states at the same time, as long as no one sees it. But as soon as any viewer looks into the room, the cat's fate is unequivocally sealed. The viewer will find the cat in the room when it is definitely either alive or dead. "Such a situation is impossible, since the paradox of Schrödinger's cat contradicts the everyday intuition of each and every person regarding the behavior of large bodies, whether they are living or inanimate," claims Prof. Lifshitz. According to him, physicists routinely measure such integrated quantum states in their laboratories, as long as they are objects whose size does not exceed several atoms (the record as of today is the C60 molecule made of sixty carbon atoms arranged in the shape of a football). At the same time, he points out that what physics still does not know how to explain is why quantum theory, which so accurately describes the behavior of particles at the atomic and subatomic level, is not valid for large objects.

According to one hypothesis, as claimed by the physicist, winner of the Wolf Prize, Sir Roger Penrose, the explanation comes from the very fact that the mass of large objects is too large. For example, as Penrose claims, a heavy object in a combined state - known by physicists as the "cat state" - where it is in two different places at the same time will exert such a great gravitational force on itself that it will destroy the cat state in which it is found. On the other hand, the more accepted explanation, as explained by the Nobel laureate physicist Anthony Leggett, is that quantum theory is valid for large objects, but their continuous contact with their environment does not allow them to be in cat states. The environment, according to Leggett and many others, plays the role of the observer who looks into the room and determines the cat's fate, thus preventing large objects from demonstrating to the physicist in the laboratory the fact that they do indeed comply with the laws of quantum theory.

The question asked is where is a solution to the cat paradox expected from? It is possible that the nanotechnology developments of recent years will allow physicists to test these various hypotheses in the foreseeable future. The idea is to examine the behavior of nanomechanical oscillators - a kind of tiny guitar strings, the thickness of which does not exceed a few nanometers (a nanometer is one millionth of a millimeter) - which oscillate at frequencies in the gigahertz range. This is a frequency similar to the electronic clocks in personal computers, except that here we are dealing with a huge number of atoms moving together. It is possible that the combination of very high frequencies and very low temperatures will make it possible in the future to predict quantum cat states of these relatively large objects, provided that it is possible to isolate them from their surroundings if necessary. Such an observation would be decisive in favor of Leggett's claim. But this task is not easy, and it seems that many years will pass before we can observe such situations.

Instead of waiting for the day when it will be possible to produce exotic cat states in the laboratory using nanomechanical devices, the nanomechanics group headed by Prof. Ron Lifshitz from Tel Aviv University proposes to test the validity of quantum theory regarding nanomechanical oscillators in a simpler way, by examining their dynamic behavior - by measuring The way they move through time. The reason this idea has not been proposed so far lies in the fact that it is doomed to failure as long as we are dealing with simple oscillators whose behavior is linear. These are the common oscillators, like a weight hanging on a spring, whose oscillation time does not depend on the intensity of their oscillation. Although in general quantum theory predicts a different dynamic behavior than that predicted by Newton's classical theory, there is no significant difference regarding linear oscillators. The researchers from Tel Aviv University showed with the help of theoretical calculations how this problem can be overcome by means of non-linear nanomechanical oscillators, whose oscillation time shortens as the intensity of their oscillation increases.

A graphic description of the location of the oscillator, some time after it began to oscillate, based on the calculations of Itamar Katz and his partners. On the right is depicted an oscillator that behaves classically and on the left an oscillator that behaves quantumly. A similarity can be identified between the blue areas where there is a high chance of finding the oscillator (the horizontal axis indicates the position of the oscillator in space, and the vertical axis its speed). It can also be seen that the quantum oscillator spends time in regions that the classical oscillator is prevented from entering, where the regions indicated in red do not even have an explanation in classical terms. Prof. Lipshitz and his group believe that it will be possible to notice such differences in laboratory experiments in the near future. The drawing is taken from the article published these days in the Physical Review Letters newspaper.