The calculations that the scientists wanted to carry out were so complex that even supercomputers could not do it.
How does the quantum world work?
Calculate the movement of one billiard ballrelatively simple. But predicting the trajectories of a million gas particles in a vessel, which are constantly colliding, braking and deflecting, is much more difficult. If it is not clear exactly what speed each particle is moving at, then they have an infinite number of possible options at any given point in time. Only probability matters.
A similar situation exists in the quantum world:quantum mechanical particles can simultaneously possess all potentially possible properties. This makes the state space of quantum mechanical systems incredibly large. To model the interaction of quantum particles with each other, it is necessary to take into account all their variant states. And it's incredibly difficult.
The point is that the computing requirementsincrease exponentially with the number of particles. If you take more than 40 particles, then even the fastest supercomputers will not be able to cope with them. This is one of the greatest challenges in quantum physics.
How to simplify the task?
In the new study, scientists usedmethods from the field of machine learning—artificial neural networks. With their help, it is possible to reformulate the quantum mechanical state, making it controllable by computers.
Artificial intelligence digital transformation concept. Photo: rawpixel.com
Using this method, physicists investigated importanta theoretical prediction that has so far remained unclear is the quantum Kibble-Zurek mechanism. It describes the dynamic behavior of physical systems during the so-called quantum phase transition. A simple example of a phase change is when water turns into ice. Another example is the demagnetization of a magnet at high temperatures.
But if you do the opposite and vice versa,and cool the material, the magnet will again begin to “work” below a certain critical temperature. However, this occurs unevenly throughout the material. Instead, many small magnets are created simultaneously with their north and south poles aligned differently. As a result, the resulting magnet is actually a mosaic of many different smaller magnets. In addition, it will be defective.
Previously, in another study, scientists confirmedKibble-Zurek scaling for defect formation in a nematic liquid crystal system. There, the transition from a homogeneous state to a defective state was achieved using an electric field. The scale index α=1/2 was obtained for various materials and does not depend on temperature.
Source: https://doi.org/10.1002/cphc.201700023
The Kibble Mechanism—Zurek is named afterTom V. B. Kibble, who was a pioneer in the study of domain structure formation in the early Universe, and Wojciech H. Zurek, who related the number of defects created to the critical parameters of the transition and its speed.
The Kibble-Zurek mechanism predicts how muchof these defects are to be expected. Simply put, how many mini-magnets will the material ultimately consist of? It is noteworthy that the number of these defects is universal and, thus, does not depend on microscopic details. This means that many different materials behave in exactly the same way, even if their microscopic composition is completely different.
The Kibble-Zurek mechanism and the formation of galaxies after the Big Bang
Initially, the Kibble-Zurek mechanism was introducedto explain the formation of structure in the Universe. After the Big Bang, it was initially completely homogeneous, which means that all the containing matter was distributed evenly. For a long time it was unclear how galaxies, stars or planets could form from such a homogeneous state.
In this context, the Kibble-Zurek mechanismhelps you understand what happened. As the Universe cooled, defects developed like magnets. And, if these processes in the macroscopic world are well studied, there is one type of phase transitions on which it has not yet been possible to test it. We are talking specifically about quantum phase transitions.
Universe expansion, 3D rendering. Photo: angel_nt
The problem is that they only exist whenabsolute zero temperature: −273 °C. This means that the phase transition occurs not during cooling, but due to a change in the interaction energy. For example, when the pressure changes.”
What have the scientists done?
In a new study, scientists modeledsuch a quantum phase transition on a supercomputer (with the help of artificial neural networks). Thus, they showed for the first time that the Kibble-Zurek mechanism, which explains the birth of the Universe, is also applicable in the quantum world. As the study authors note, this finding was “not obvious.” It took a lot of effort to prove them. The new research will allow physicists to better describe the dynamics of quantum mechanical systems of many particles. And, therefore, to more accurately understand the rules that govern this exotic world.
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On the cover: NASA's Goddard Space Flight Center Conceptual Image Lab