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For most of our history, human
technology consisted of
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our brains, fire, and sharp sticks.
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While fire and sharp sticks became
power plants and nuclear weapons,
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the biggest upgrade has
happened to our brains.
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Since the 1960s, the power of our brain
machines has kept growing exponentially,
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allowing computers to get smaller
and more powerful at the same time.
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But this process is about
to meet its physical limits.
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Computer parts are approaching
the size of an atom.
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To understand why this is a problem,
we have to clear up some basics.
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A computer is made up of very simple
components doing very simple things,
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representing data, the means of processing
it, and control mechanisms.
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Computer chips contain modules,
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which contain logic gates,
which contain transistors.
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A transistor is the simplest form
of a data processor in computers,
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basically, a switch that
can either block or open
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the way for information coming through.
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This information is made up of bits,
which can be set to either zero or one.
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Combinations of several bits are used to
represent more complex information.
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Transistors are combined to create logic
gates, which still do very simple stuff.
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For example, an AND gate sends an output
of one if all of its inputs are one
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and an output of zero otherwise.
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Combinations of logic gates finally
form meaningful modules,
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say, for adding two numbers.
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Once you can add, you can also multiply,
and once you can multiply,
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you can basically do anything.
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Since all basic operations are literally
simpler than first-grade math,
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you can imagine a computer as
a group of seven-year-olds
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answering really basic math questions.
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A large enough bunch of them can compute
anything, from astrophysics to Zelda.
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However, with parts
getting tinier and tinier,
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quantum physics are making things tricky.
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In a nutshell, a transistor
is just an electric switch.
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Electricity is electrons moving
from one place to another,
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so a switch is a passage that can block
electrons from moving in one direction.
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Today, a typical scale
for transistors is 14 nm,
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which is about 8 times less
than the HIV virus’s diameter
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and 500 times smaller
than a red blood cell’s.
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As transistors are shrinking
to the size of only a few atoms,
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electrons may just transfer themselves to
the other side of a blocked passage
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via a process called quantum tunneling.
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In the quantum realm, physics
works quite differently from
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the predictable ways we’re used to,
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and traditional computers
just stop making sense.
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We are approaching a real physical
barrier for our technological progress.
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To solve this problem,
scientists are trying to
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use these unusual quantum
properties to their advantage
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by building quantum computers.
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In normal computers, bits
are the smallest units of information.
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Quantum computers use qubits, which
can also be set to one of two values.
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A qubit can be any
two-level quantum system,
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such as a spin in a magnetic field
or a single photon.
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Zero and one are this
system’s possible states,
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like the photon’s horizontal
or vertical polarization.
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In the quantum world, the qubit
doesn’t have to be in just one of those;
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it can be in any proportions
of both states at once.
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This is called superposition.
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But as soon as you test its value, say,
by sending the photon through a filter,
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it has to decide to be either
vertically or horizontally polarized.
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So, as long as it’s unobserved, the qubit
is in a superposition of probabilities
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for zero and one, and you can’t
predict which it will be.
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But the instant you measure it, it
collapses into one of the definite states.
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Superposition is a game-changer.
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Four classical bits can be
in one of 2 to the power of 4
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different configurations at a time.
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That’s 16 possible combinations,
out of which you can use just one.
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Four qubits in superposition, however,
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can be in all of those
16 combinations at once!
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This number grows exponentially
with each extra qubit.
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20 of them can already store
a million values in parallel.
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A really weird an unintuitive
property qubits can have
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is entanglement, a close connection that
makes each of the qubits
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react to a change in the other’s
state instantaneously,
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no matter how far they are apart.
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This means that when measuring
just one entangled qubit,
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you can directly deduce properties of
its partners without having to look.
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Qubit manipulation
is a mind-bender as well.
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A normal logic gate gets
a simple set of inputs
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and produces one definite output.
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A quantum gate manipulates
an input of superpositions,
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rotates probabilities, and produces
another superposition as its output.
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So a quantum computer sets up some qubits,
applies quantum gates to entangle them
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and manipulate probabilities,
then finally measures the outcome,
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collapsing superpositions to an
actual sequence of zeros and ones.
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What this means is that you
get the entire lot of calculations
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that are possible with your setup
all done at the same time.
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Ultimately, you can only
measure one of the results,
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and it will only probably
be the one you want,
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so you may have to
double-check and try again.
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But by cleverly exploiting
superposition and entanglement,
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this can be exponentially more efficient
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than would ever be possible
on a normal computer.
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So, while quantum computers will probably
not replace our home computers,
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in some areas they are vastly superior.
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One of them is database searching.
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To find something in a database,
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a normal computer may have
to test every single one of its entries.
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Quantum algorithms need only
the square root of that time,
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which for large databases
is a huge difference.
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The most famous use of quantum
computers is ruining IT security.
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Right now, your browsing,
email, and banking data
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is being kept secure by an encryption
system in which you give everyone
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a public key to encode
messages only you can decode.
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The problem is that this
public key can actually be used
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to calculate your secret private key.
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Luckily, doing the necessary math
on any normal computer
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would literally take
years of trial and error.
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But a quantum computer
with exponential speedup
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could do it in a breeze.
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Another really exciting
new use is simulations.
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Simulations of the quantum world
are very intense on resources,
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and even for bigger structures,
such as molecules,
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they often lack accuracy.
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So why not simulate quantum physics
with actual quantum physics?
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Quantum simulations could provide
new insights on proteins
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that might revolutionize medicine.
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Right now we don’t know
if quantum computers will be
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just a very specialized tool
or a big revolution for humanity.
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We have no idea where
the limits of technology are,
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and there’s only one way to find out!
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This video is supported by
the Australian Academy of Science,
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which promotes and
supports excellence in science.
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Learn more about this topic
and others like it
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at .
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It was a blast to work with them,
so go check out their site!
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Our videos are also made possible
by your support on Patreon.com.
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If you want to support us and become part
of the Kurzgesagt bird army,
-
check out our Patreon page!