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. 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 33 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.”
