SEPTEMBER 22, 2020

Author: Jinkyung Kim
IBS Center for Quantum Nanoscience, Ewha Womans University Doctoral Candidate
The topic of this “Spin Art” art contest is the spin in quantum mechanics. Quantum mechanics is an academic study that deals with a world that is even smaller than the atoms. Atoms and molecules make up all matter on earth. Sometimes, surreal things happen in such a small world. Among those, there is the concept of spin. Spin has unique properties, including “discontinuity,” “superposition,” and “entanglement.” We are holding a contest to artistically express these characteristics. The characteristic of spin has been explained below by comparing it to the work of the Surrealist artist René Magritte, to enhance general understanding of artists who communicate with visual language.
(It may be unrelated to the original intentions of René Magritte).
Hello! I am Spin and I live in a world dominated by quantum mechanics. I am a physical quantity that determines the magnetic properties of particles. A physical quantity is a ‘value’ like mass or speed. Thanks to me, particles such as electrons and neutrons behave as very small magnets because the magnetic property of an object changes depending on my state.

People call me spin because they believe that I exist when a particle “spins” around a single axis. People compare me to our earth as it rotates around its own axis, an imaginary line running through the North and South Poles. However, I only exist in places that are much smaller than the earth. If you imagine the earth to be as small as an apple, the world I live in would be as small as shrinking the apple placed on the earth by the ratio of earth to apple. Many unusual things that you cannot see in the normal world happen in such a small world. It is almost comparable to a world illustrated in the works of a Surrealist artist, who took great interest in exploring dreams and the unconscious mind. I would like to introduce myself through the works of René Magritte, a Surrealist artist.

Discontinuity: Maybe the World Moves the Way the Second Hand of a Clock Moves

If we look carefully at René Magritte’s “Le blanc-seing”, we can see that some parts of the woman who is riding a horse have been cut off. Generally, when we imagine a woman riding a horse, we imagine the shape to be fully connected throughout. Similarly, in a world that people live in, various values such as mass or speed exist continuously. However, in a world that is as small as a particle, physical quantities such as spin, exist in discontinuity as shown in the picture. Magritte intentionally cut the image when painting it. In a particle world, some values such as energy exist in a discontinuous manner under the law of nature, like this painting. The concept of having a lump sum that cannot be divided and has discontinuity is called ‘quantization’.

The energy of particles is quantized in a very small world. This means that it is only possible to choose energy values that were already determined. To illustrate, generally I am in a calm state. My excitement grows when I am energized. However, the amount of excitement that I can experience (or the amount of “energy steps I can climb” in excitement) is pre-determined. Particles that follow the quantization rule and “climb” a specific number of energy steps are called ‘quantum particles.’ Most of quantum particles have spin. A quantum particle can be on certain energy steps depending on its spin’s orientation. An electron, for an example, has spin 1/2 and can be on energy steps expressed in numbers -1/2 (down spin) or +1/2 (up spin). The electron switches between -1/2 and +1/2 energy steps when it absorbs or emits a quantum of energy. Other quantum particles have different values of spins which is multiples of integer (0, 1, 2 … ) or half integer number (1/2, 3/2 … ). For another example, a photon has spin number 1. Quantum mechanics is the academic field that studies how these quantum particles or quantum states behave, as well as the rules or the aforementioned quantization.

Do you remember how I introduced myself as a very small magnet at the beginning? The type of the magnet changes depending on the step I live in. The most basic physical step is when I am in the ‘Spin 1/2 state.” As I mentioned above, I can go to just two different steps. I will explain a little more about these steps in the next piece.

Superposition: I can Simultaneously Exist during the Day and at Night

Have you ever thought about a world in which both day and night exist at the same time? In Magritte’s “The Empire of Light”, the presence of light that makes the day bright exists at the same time with the absence of light, which makes the night dark. This situation also exists in the quantum world because different states of quantum properties can exist simultaneously.

Let us assume the ‘spin 1/2 state’, from which I can only move into two different steps which are -1/2 (down spin) or +1/2 (up spin). Similar to how both daytime and nighttime are portrayed in the same piece, I can simultaneously exist in two different states. Please don’t get me wrong! I am not referring to an ambiguous state, like a sunset that occurs between day and night. I am saying that two different states can exist simultaneously while maintaining separate states, due to quantization. This is hard to imagine because it is a fundamental difference between the quantum world and the “real world”. When it is difficult to grasp, think of Magritte’s painting that portrays day and night as separate but together. Expressed in terms of probability, 50% of myself is in one state while the other 50% simultaneously exists in another state. This is the ‘superposition’ property of quantum mechanics.

Entanglement: The Other One can be Figured out by Reading the First One

In Magritte’s “The Human Condition 2”, we cannot distinguish between the landscape and the painting. It is unclear whether or not the landscape is being seen through a hole, or if the entire image is part of the painting. The ocean and the canvas are far apart from one another, but the horizontal line makes it seem as if two separate spaces are connected.

If there were crashing waves on the ocean in the canvas, we would expect there to be crashing waves on the ocean outside as well, without actually going outside to check. In a quantum world, such a closely connected state is called “entanglement.”

Let us assume that I am entangled with another spin. Being entangled is the same as sharing information between friends. Therefore, by becoming aware of my state, one could figure out the state of the spin that I am entangled with. In this case, something very subtle happens. Even if my friend and I are on the opposite ends of the universe, knowing my state would immediately expose the information that my friend has. This phenomenon is comparable to how we view Magritte’s painting. By viewing one side of the painting, we can immediately decipher the other. Don't you think this is marvelous? In the “real world,” it would take an extremely long time to find information from the opposite end of the universe.

Due to these properties, the spin can be very useful. Spin, as it is like a very small magnet, can be used as an information storage, in the same way that computers store information using digits 0 and 1. However, since information is shared when spins are entangled, it is possible to create communication systems or computers that are extremely quick. These are found in technologies such as quantum cryptography, quantum computers, and quantum transmission.

It is Possible to Change with my Environment!

I will tell you more about how I live as a spin in the quantum world. In Magritte’s “The Hesitation Waltz”, there are apples wearing masks. Apples wearing masks! As I tell you, these apples may look like people’s faces. It conveys the idea that apples are feeling serious even when they do not have eyes, noses, or mouth. Just placing masks on the apples makes them appear different from normal apples.

This is because we also consider the surrounding environment when we judge a certain subject. If there were no masks, apples would seem like normal apples on a table. Ultimately, the effect of the masks on the apples made the apples have a different impression on the audience.

It is the same for spin. I can stay alone, but I also interact with the environment surrounding me. Therefore, my property sometimes changes when the environment changes. If the type of the surface I am on changes I can adopt a new and different magnetic property. Similar if I get closer to another spin, our spinning motion is coupled like dancers waltzing together. In this case, our spin properties such as our energy steps change too. However, I return to my original state when I move away from that environment. Despite existing alone, the quantum mechanical environment around me influences me.

Everyday Life Created by Spin

Magritte’s work makes us think about new and unfamiliar things that we rarely encounter in our daily lives. People sometimes discover the other side of reality or face unfamiliar feelings when they see the novel ideas of Magritte, that break away from common sense. It is the same for the quantum mechanical world where I live in. New natural law that people never even imagined of is governing this small world.

The discovery of quantum mechanics was so shocking that it completely changed the existing view of the physical world. Afterwards, it was revealed that there are many more novel properties in addition to discontinuity, superposition and entanglement.

It may seem like a completely different world because it is so small and unfamiliar, but spins are actually closer to people’s life than it seems. Light, any object composed of atoms, smartphones in front of your eyes, and even devices such as quantum computers. People are already doing many things with quantum mechanics, especially by using the value called spin. Quantum mechanics is no longer something that is shocking or unfamiliar. It is becoming part of everyday life on our planet. Would you like to learn more about the world-changing quantum mechanics and spin?