We are in the quantum: Physicists observe live how an observer influences reality

Researchers from the Korea Institute of Basic Sciences (IBS) have quantified for the first time the wave-particle duality of the quantum world and observed in real time the mechanism that allows the observer to interfere with reality.

Wave-particle duality is a concept of quantum mechanics according to which there are no fundamental differences between elementary particles and waves, since particles can behave like waves and waves like particles.

Consequently, quantum objects are complementary, that is, their two fundamental qualities cannot be measured at the same time: either the wave dimension is measured, or only the particle dimension, as established by Niels Bohr in 1927.

The electron, for example, is a wave and a particle at the same time, but it is described by a wave function: it is the one that facilitates the probability of finding it somewhere to use it in any technological function (electronics).

Quantum physics is therefore essentially probabilistic, unlike classical physics, which is deterministic (it can pinpoint the next solar eclipse).

Despite its unpredictability, quantum physics has enabled the development of technologies unimaginable in the 19th century, such as quantum information and communication, metrology, imaging, and quantum detection.

Unsolved problems

Unsolved problems However, in quantum science there are still unsolved and even incomprehensible problems, like the same wave-particle duality and complementarity, among other paradoxes.

Scientists at the Korea Institute of Basic Sciences (IBS) have obtained a new and more quantitative basis for the mysterious wave-particle duality that better illuminates this quantum quality.

In a twist on the classic double slit experiment, used precisely controlled photon sources to measure in real time the degree of wave and particle of a photon as it passes through an obstacle.

Their results, published in Science Advances, show that the properties of the observer (a sensor) influence the wave and particle character of the photon. This discovery complicates and challenges the common understanding of complementarity, points out about it the PhysicsWorld magazine.

The labyrinth of the double slit

The labyrinth of the double slit Young’s experiment, better known as the double slit experiment, conceived in 1801 by Thomas Young to find out the corpuscular nature of light, has been essential to demonstrate the wave-particle duality.

It is an experiment that contains all the magic of the quantum world, as it reveals two things: that, at an elementary level, physical objects can behave as a set of particles (and cannot, for example, cross a physical barrier) or also as a wave that passes through obstacles, such as radio waves that pass through walls.

Young’s experiment also reveals something even more unusual: that measurement or observation influences the behavior of particles, determining that they manifest as waves or corpuscles. It occurs with photons, electrons, protons, or neutrons.

What happens in the double slit experiment? It is difficult to describe, because at some point in its development any of these particles will have to “decide” what to do when it encounters a wall that it cannot pass through. At that moment, he “observes” that he has two slits that make him “think”: what if I go through it like a wave, passing through the slits?

Interference pattern

Interference pattern In the end, she makes up her mind and goes through the wall through the two slits, turned into a wave. Once located on the other side of the wall, it becomes a particle and bumps into a posterior wall that has no cracks: then it hits a place on the second and impassable wall and leaves a mark.

The experiment has its crumb: as more particles wave through the double slit, the second wall reflects the impacts of the particles into which they have become again, but they do not cluster randomly (as might be expected) , but following an order that would be determined by its wave behavior. This order is called the interference pattern.

And the most surprising thing: this whole process happens because we are observing it. When the waves pass through the slits, they “realize” that there is a detector and they react by becoming particles. They “manage” to appear in the photo by noticing the detector (an interferometer).

The principle of complementarity states that both experimental results, both the particle and the wave, are necessary to fully understand the quantum nature of, for example, a photon.

Seduced photon

Seduced photon The new study has delved into these paradoxes and determined that the properties of the slits are also important for the wave-particle duality to occur.

The researchers improved the detector present in the slit and enhanced the attraction it awakens in a photon so that it can pass through the wall.

This allowed the researchers to better appreciate when the photon mutates from particle to wave and to determine how its wave nature is reflected in the interference pattern that appears on the second wall.

That means, the researchers emphasize, that, during the experiment, the photon changes from particle to wave and then back to particle, not only by its own decision, but also influenced by the detector placed in the slit that allows it to pass.

It also means that the impacts on the wall without slits follow an (interference) pattern that emanates from its wave behavior. In this way, the particle records the fleeting moment in which it was a wave, a kind of memory crystallized on the second wall.

We are in the quantum

We are in the quantum The new experiment seems to confirm what Bohr said in the 1920s: that we are not mere observers of what we measure, but also actors. We are in the quantum.

The new double-slit experiment says something else. It explains how this interaction between the observer and reality takes place: through the sensor located on the grid, it exerts an attraction on the photon to encourage it to dance between the wave and the particle, depending on our scientific interests (that it manages to cross the wall and observe the whole process in detail).

Researchers point out in a release: “Richard Feynman once said that solving the puzzle of quantum mechanics lies in understanding the double slit experiment.”

The new discovery brings us closer to that understanding, without ending the yet-to-be-discovered mysteries that are still associated with the double-slit experiment.

Reference: Quantitative complementarity of wave-particle duality.

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