What is Quantum Superposition?


For people who, in one way or another, tried to familiarize themselves with the basic concepts of quantum mechanics, such a term as “quantum superposition” is known, which tells us that an object can be simultaneously in several quantum states until we start to observe it.

This effect is clearly seen in the experiment with two slits. Once we have a light source, a baffle with two parallel slits, and a projection screen. When illuminating the screen through a partition, we will see an interference pattern (amplification or weakening of illumination when superimposed waves of light with the same frequency), on the screen it looks like vertical light stripes intersecting with dark ones.

Interference is characteristic of waves, which means that light is a wave. But, on the other hand, if we emitted light in portions and, for example, put a detector in order to fix which of the slits the light passes through, then the interference pattern would disappear and we would see two light stripes, as if small particles passed through the slits and hit the screen, projecting images of the slits. Therefore, scientists believe that light is both a wave and a particle at the same time, and it behaves in different ways depending on the conditions.

In physics, all processes are described by equations and the double-slit experiment is no exception. Even if only the first slot is open, then the solution of the wave equation is a certain number A, and if the second solution is B. The superposition principle says that the general solution for two open slots is just the sum of solutions for each of the slots (A + B). However, something new has surfaced in the three-slit experiment.

The fact is that when two slits are open simultaneously, then the particle somehow passes through both slits at the same time and interacts with itself.

In the experiment with three slits, approximately the same thing happened, but the experimental data were not the sum of the solutions for three slits, which the scientists expected, this meant that there was some missing element, which means that everything is not as easy to describe as we would like. … The experiment with three slits showed that elementary particles can describe rather abstract trajectories and interact in different ways with themselves or with other quanta. Therefore, the very concept of superposition, which is described in many sources and books, is not entirely correct. The superposition state is not just the sum of several states, but takes into account some corrections for the complex interaction of particles.

Author: Vladislav Kigim. Edited by Fedor Karasenko.

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