Quantum Entanglement

Imagine that you’re on a long drive when you suddenly hear your stomach grumbling. You decide to head to a fast-food drive through and you order a hotdog and a burger. They are put in similar boxes and handed to you. You have no way of knowing which box has the hotdog and which has the burger. Obviously, once you open one of the boxes and see a burger,   you will immediately know that the other one has the hot dog. This means that the hotdog and the burger are entangled in a certain way.   

This is roughly the idea upon which quantum entanglement is based. Look around you... everything you see, perceive, and interact with in the real world follows the rules of Classical Mechanics. This is a study of the motion of bodies in accordance with the general principles first laid down by Sir Isaac Newton. But what about objects that are really, REALLY small? Do they also follow these same laws of classical mechanics? Believe it or not, the answer is NO!  When things get that small, Quantum Mechanics takes over, and things start to get extremely weird... Quantum mechanics is the language of tiny particles like photons—the particles that make up light—and particles inside an atom, such as protons, neutrons, and electrons.   

To give you a rough idea as to the size of these particles, consider this—the tip of a needle is so large that it could fit billions of elections. THAT'S how incredibly small electrons are. Now that you have a general idea of the size of electrons, let’s talk about identities. If someone were to ask “Who are you?”, what would you say? Probably your name, right? Now, let’s assume that an anthropomorphic raccoon   from another planet asks you the same question, what would you say then? Perhaps...“I am Peter Quill, a human from Earth.” In this case, you specified 3 levels of identification. 

Similarly, in a 3D space, x,y and z coordinates are used to specify an object’s exact location, as no two objects can have the same x,y and z coordinates. If you consider a 4-Dimensional space—with time (t) as an additional dimension—then no two particles can have the same 4 coordinates. In the same way, an electron has 4 levels of identification, consisting of 4 quantum numbers. Every electron within an atom has a unique set of quantum numbers; no two electrons can share the same combination of 4 quantum numbers. 

Electrons can be identified using these 4 quantum numbers, which are called:

1) Principal quantum number

2) Orbital angular momentum quantum number 

3) Magnetic quantum number 

4) Electron spin quantum number 

All of these quantum numbers are very important, as they help determine the   electron configuration of an atom and the probable location of electrons within the atom.

However, for the scope of this article,

we’re only going to talk about the Electron spin quantum number. 

The definition of spin is—the intrinsic value of the angular momentum of a fundamental particle. An electron can either have a positive spin (called ‘spin up’) or a downward spin (called ‘spin down’) Now this is where things get bizarre. When we say an electron has a positive spin or a negative spin, it doesn’t mean that the electron is ACTUALLY spinning. Although it does have angular momentum, and proper magnetic orientation, it’s not exactly “spinning”. It may actually exist in a state of superposition—when it has both a negative and positive spin. You may find the idea of superposition confusing,   because this doesn’t seem to go along with our perception of the real world. 

To help explain this a bit better, here’s a famous example for understanding superposition: You might have heard of Schrödinger's Cat;  it is a famous thought experiment devised by Austrian-Irish physicist Erwin Schrödinger. It goes like this… imagine you put a cat inside an opaque soundproof box, along with a radioactive substance, a vial of poison and a Geiger counter. If the radioactive substance decays, then the Geiger counter triggers a setup that releases the poison, killing the cat. But the decay of the substance is a random process, so there’s no way to predict when it will happen. And that is why, before opening the box, you can say that the cat is in a superposition of being both alive and dead at the same time. In the same way, when a coin spins on a flat surface, it’s in a state of superposition between its two faces—head and tails. Similarly, electrons in their natural state exist as a superposition of both up and down spin. Only when measured do they give a definite value of up or down, which, in technical terms, is referred to as the “collapse of the wavefunction”. In quantum mechanics, wave function collapse occurs when a wave function, which was initially in a superposition of a few states, reduces to a single state due to interaction with the external world. 

When a pair of electrons are generated, interact, or share spatial proximity, their spin states can get entangled, which is what scientists call the quantum entanglement of electrons. Once the electrons are entangled, the two electrons can only have opposite spins, that is, if one is measured to have “up spin”, the second immediately becomes down spin. Now, we know that the two electrons, unmeasured, do not have a single spin, but a superposition of both up and down spin. If we were to separate the two electrons arbitrarily far, say, we put one in a Physics lab on Earth and another in a different lab somewhere in the Andromeda galaxy, and we measure the spin of the electron on Earth, we will immediately know the measurement of the one in the Andromeda galaxy.

For example, if we measure the Earth electron to have up spin, we immediately know that the other electron has down spin. This information traveled instantaneously, and faster than the speed of light! As one can imagine, this idea greatly bothered famous physicist Albert Einstein. It was such a disturbing realization, in fact, that he called this phenomenon:  “spooky action at a distance”. So how can this ‘spooky action at a distance’ be useful to us? Well, let's start with one of the most common everyday objects—the clock. Having a common synchronized clock is very important in today's world. They keep things like stock markets and GPS systems in line. Today, we have extremely precise clocks, known as atomic clocks. The quantum-logic clock at the U.S. National Institute of Standards and Technology (NIST) in Colorado will neither lose nor gain one second in some 15 billion years (which is roughly the age of the universe). Entangled atomic systems would not be pre-occupied with local differences and would instead solely   measure the passage of time, effectively bringing them together as a single pendulum. That means adding 100 times more atoms into an entangled clock would make it 100 times more precise. Entangled clocks could even be linked to form a worldwide network that would measure time independent of location, vastly expanding the technology of GPS systems and telecommunication. Then, of course, there’s quantum cryptography. As a kid, have you ever made up a secret code language that only you and your best   friend could understand? Imagine that, but with the key to cracking the code being randomly polarized photons entangled with each other. That is quantum cryptography!

Today, some tech companies use QKD (Quantum Key Distribution)   to design ultra-secure networks. In 2007, Switzerland tried out an ID  Quantique product to provide a tamper-proof voting system during an election. This system promises to be highly secure, because if the photons are entangled, any changes to their quantum states made by intruders would be immediately apparent to anyone monitoring the system. 

Researchers at Japan’s Hokkaido University developed the world’s first entanglement-enhanced microscope using a technique known as differential interference contrast microscopy. Using entangled photons greatly increases the amount of information the microscope can gather, as measuring one entangled photon gives information about its partner.

How about quantum teleportation… is it possible? Yes, teleportation is possible in the world of subatomic particles, but it’s entirely different from the way teleportation is depicted in movies and popular culture. Quantum teleportation involves the transportation of information, rather than the transportation of matter, which is the type of teleportation typically focused on in science fiction. Physicists continue to delve into and understand more about the capabilities of quantum entanglement. Once we are able to harness this knowledge, it could potentially revolutionize every aspect of our existence. Until then, we will continue to try and make sense of the principles of quantum mechanics, because, let’s face it, it’s a strange branch of science that doesn’t   seem to make any sense in the REAL world. Basically, as Nobel laureate Richard Feynman once said,  “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”