Imagine looking at a fast but fragile butterfly. While it flutters, it is rather difficult to study it in detail, so you need to pick it up. But as soon as it was in your palms, the wings crumpled and lost color. It's just that the butterfly is too vulnerable, and any impact you have will change its appearance.
Now imagine a butterfly that changes its appearance from one glance. This is how single electrons behave in a solid. As soon as scientists "look" at an electron, its state is already different from the original. This fact significantly complicates the study of solid state physics - a field of science that describes the properties of solids (all substances with a crystal lattice) in terms of their atomic structure. The creation of computers, telephones and many other devices, without which we cannot imagine life, is the merit of this branch of science.
If the electrons cannot be "seen", they must be replaced with something larger, the scientists decided. Candidates for the place of electrons must preserve their properties in such a way that the equations describing processes in a solid remain unchanged. Atoms at ultra-low temperatures have come to this role. In the physical world, temperature is analogous to energy: the lower it is, the more motionless the object becomes. At room temperature, an oxygen atom in air moves at a speed of several hundred meters per second, but the lower the temperature, the slower its speed. The minimum temperature in our world is considered to be zero degrees Kelvin, or minus 273.15 ° C.
Comparison of the behavior of atoms in a solid at room temperature and atoms at ultralow temperatures / Illustration by RIA Novosti. A. Polyanina
Ultracold atoms are cooled to microkelvin or less, where the speed of movement is only a few centimeters per second.
From such atoms and an optical lattice, scientists have created an artificial crystal similar in structure to natural solids. The very optical lattice, which takes on the role of the atomic lattice of a solid, is created using lasers whose rays intersect at specified angles. By controlling the position of the lasers and their power, one can continuously change the geometry of the lattice, and by imposing an additional field, switch the interaction between the "electrons" from repulsive to attractive.
This is how the artist imagines an artificial crystal lattice / Illustration by RIA Novosti. A. Polyanina
But to conduct experiments, it is necessary to control the movement of electrons. They are susceptible to electric and magnetic fields because they have a charge. The atoms replacing electrons in an artificial crystal are neutral, so it was necessary to come up with a replacement for the force that controls them. The electric field has been successfully replaced by gravity, which is responsible for the rectilinear motion of the electron. However, electrons in a magnetic field twist, their trajectory can be described as a spiral. Therefore, researchers have created a synthetic magnetic field that has the same effect on moving atoms as a real magnetic field, which is the main condition for studying fundamental laws.
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Diagram of the movement of electrons in an electromagnetic field / Fotolia / Peter Hermes Furian
Thus, physicists were able to study the properties of any solids (metals, semiconductors, dielectrics), experiment with them and change them at will. It turns out that scientists have created a kind of "designer" - a system that simulates the properties of the quantum world of electrons, but, unlike it, is easily accessible for research.
Other systems can be assembled from the "quantum constructor", including those that do not exist in nature. For example, all elementary particles are divided into bosons and fermions. Bosons have an integer spin number, and fermions have a half-integer. Using isotopes of atoms, it is possible to convert electrons in the artificial solid discussed above from fermions to bosons.
“In addition to the problems of solid state physics, quantum constructors based on cold atoms can be used to solve problems from other areas, for example, elementary particle physics,” explains the chief researcher of the laboratory of the theory of nonlinear processes at the Institute of Physics of the Siberian Branch of the Russian Academy of Sciences and professor of the Department of Theoretical Physics at Siberian Federal University, Doctor of Physics and Mathematics Andrey Kolovsky. - The interaction between elementary particles is carried out through the so-called gauge fields. The electromagnetic field familiar to us from school, responsible for the interaction between charges, is a special case of gauge fields. In principle, fields other than electromagnetic fields can be modeled, and such studies are already underway. Another area is astrophysics, where scientists, using cold atoms,simulate the thermodynamics of black holes”.
Such constructors can also be used to assemble quantum computers, with the help of which it is convenient to study the teleportation of quantum particles.
And also look into the distant future, 20-40 billion years ahead, because the Universe is constantly expanding and, according to the laws of thermodynamics, its temperature is gradually dropping. Over time, it will cool down to nanokelvins, and thanks to quantum simulators, we will be able to observe its state right now.