Imagine that you are on a long drive, when you suddenly hear your stomach begin to grumble.
You decide to head to a fast food joint, where you order a hot dog and a hamburger.
They're put in similar boxes and handed to you through the window.
You have no way of knowing which box has the hot dog 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 hot dog and the burger and 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 electrons. THAT'S how incredibly small electrons truly 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:
Principal quantum number Orbital angular momentum quantum number
Magnetic quantum number 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 video,
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 preoccupied 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.”