Experiment scheme
Scientists have proposed measuring spontaneous current deflections, or so-called shot noise, to detect microscopic heat fluxes and special quantum states – Majorana zero modes. Their discovery will lead to the creation of new quantum computers that are capable not only of performing a large number of simultaneous computations, but also resistant to any distortion and interference of the environment. This work was supported by the Russian Science Foundation (RSF) and published in the journals Physical Review B and Semiconductor Science and Technology.
Ettore Majorana, an Italian physicist after whom the mysterious Majorana modes are named, disappeared without a trace and inexplicably in 1938. However, before his disappearance, he managed to publish one of the possible solutions of the famous Dirac equation – the fundamental equation of quantum mechanics, which combined the theory of relativity and the wave nature of particles with the property of proper rotation (spin). Majorana described a particle that is at the same time its own antiparticle – a twin with the same mass and spin, but with other characteristics of the opposite sign. If the same particle is positively and negatively charged, then its total electric charge must be zero. Similarly, with the rest of the properties, therefore, there are no ways to measure them at all. But the mysterious hypothetical “majorana” must have unusual and promising qualities for science. This went beyond the concepts of ordinary physics, but gave rise to a new direction of the most complex fundamental research.
Scientists from the Yu.A. Osipyan Institute of Solid State Physics (Chernogolovka) with colleagues from the Skolkovo Institute of Science and Technology (Moscow), Princeton University (USA) and the Walter Schottky Institute (Germany) are developing an original method for detecting zero Majorana modes – difficult to achieve states , in which “majorana” can have very low (zero) energy.
“Majorana modes, predicted by the famous physicist Alexei Kitaev 20 years ago, could become the basis of a new type of quantum computers. Although very intensive searches for them have led to a real technological breakthrough, they have not yet been crowned with success. This is largely due to the fact that the so-called “majorana” have neither charge nor spin, and their key property – nonlocality – is difficult to demonstrate using usual experimental methods, ”says one of the authors of the study, Vadim Khrapai, Ph.D. Head of the Laboratory of Electronic Kinetics, Institute of Solid State Physics, Russian Academy of Sciences.
Nonlocality is understood as the property that it is possible to influence an object without directly interacting with it, as if pressing the switch lit a light bulb just lying on the table – in fact, the signal is transmitted to where it cannot be expected.
Almost such an “incredible” experiment was carried out by the authors of the work: they passed electricity through a semiconductor wire less than 100 nanometers thick from one contact to another, but there was a superconductor in the path of the current. This material has no resistance at low temperatures, and therefore charge carriers must flow through it, as in a more “convenient” way, without reaching the end point. However, in the course of the experiment, physicists discovered a thermal (seemingly “impossible”, and therefore nonlocal) signal at the second contact, that is, the original flow was split – the electric charge went into the superconductor, and the heat farther along the wire.
The researchers were able to detect the heat signal by observing very small random fluctuations in electric current, known as shot noise. This name reflects modern ideas that the electron charge is indivisible, which means that the flow of an electric current does not look like a continuous stream of water, but like a stream of rain, in which each drop (or pellet) carries an elementary charge. Surprisingly, the noise of such a “rain” will tell you what size each drop is.
“Often, to detect a physical effect, we measure the electric current, that is, the average amount of charge flowing per unit of time. In the case of, for example, Majorana particles, this approach is completely ineffective, since each particle gives rise to a positive or negative charge with equal probability. On the other hand, by registering noises, one can measure the total amount of charges and the amount of heat they carry, and thus “catch” this elusive marjoram. Such a hidden effect is not only beautiful in itself, but could also be useful in the development of highly stable quantum computers, ”explains Vadim Khrapai.
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