Truly random numbers are required for cybersecurity needs, in games, for scientific modeling, etc. It would seem that what is the problem - getting a random number? Computers can easily cope with this task. However, in reality, most of the random numbers they generate are not truly random.
Computers use an algorithm to generate random numbers based on the initial position of the seed. Due to the fact that the generation process is deterministic, the numbers seem to be random, but not quite. In most cases, this is not critical, pseudo-random numbers are enough. But when it comes to, for example, data protection, this can become a problem. Given enough information about the algorithm or its output, one can find patterns in the numbers it produces. And in general, people need real random numbers.
A group of physicists at Brown University have developed a method that could potentially generate millions of random numbers per second. It uses the behavior of skyrmions, tiny magnetic anomalies that occur in some two-dimensional materials.
Published in Nature Communications, the study reveals previously unexplored dynamics of single skyrmions. Discovered about half a century ago, skyrmions aroused great interest, since their study could pave the way for the next generation of computing devices that take advantage of the magnetic properties of particles (spintronics).
A lot of research has been done using skyrmion movement to perform calculations, but this is what showed that in addition to the global movement of skyrmions through the material, local behavior of individual skyrmions can also be useful.
Skyrmions arise due to the "unwinding" of electrons in ultrathin materials. Spin can be thought of as the tiny magnetic moment of each electron that points up, down, or in the middle. Some two-dimensional materials in their lowest energy states have a property called perpendicular magnetic anisotropy, which means that all electron spins are perpendicular to the film. When these materials are excited by electricity or a magnetic field, some of the electron spins flip as the energy of the system increases. When this happens, the spins of the surrounding electrons are perturbed to some extent, forming a magnetic whirlpool surrounding the inverted electron, the skyrmion.
Skyrmions, which typically have a diameter of about 1 micrometer or less, behave like a kind of particle that sweeps through the material from side. And once they have formed, it is very difficult to get rid of them. Because they are so reliable, researchers are interested in using their motion to perform calculations and store data.
For the study, thin magnetic films were made using a technique that created subtle defects in the atomic lattice of the material. When skyrmions form in a material, these defects, which researchers call pinning centers, hold the skyrmions firmly in place rather than allowing them to move as usual.
When a skyrmion is held in place, its size fluctuates randomly. If one part of the skyrmion is pressed tightly against one anchoring center, the rest of the skyrmion jumps back and forth between the large and small diameters. This fluctuation, which occurs randomly, can be measured and used to generate random numbers.
The change in the size of the skyrmion occurs with the help of the so-called anomalous Hall effect, which is a voltage propagating through the material. This voltage is sensitive to the perpendicular component of the electron spins. When the size of the skyrmion changes, the voltage changes to a degree that is easy to measure.
The researchers calculated that by optimizing the distance between defects in their device, they could produce up to 10 million random digits per second.
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