0:00:00.195,0:00:03.313
For most of our history, human[br]technology consisted of

0:00:03.313,0:00:06.051
our brains, fire, and sharp sticks.

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While fire and sharp sticks became[br]power plants and nuclear weapons,

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the biggest upgrade has[br]happened to our brains.

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Since the 1960s, the power of our brain[br]machines has kept growing exponentially,

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allowing computers to get smaller[br]and more powerful at the same time.

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But this process is about[br]to meet its physical limits.

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Computer parts are approaching[br]the size of an atom.

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To understand why this is a problem,[br]we have to clear up some basics.

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A computer is made up of very simple[br]components doing very simple things,

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representing data, the means of processing[br]it, and control mechanisms.

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Computer chips contain modules,

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which contain logic gates,[br]which contain transistors.

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A transistor is the simplest form[br]of a data processor in computers,

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basically, a switch that[br]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,[br]which can be set to either zero or one.

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Combinations of several bits are used to[br]represent more complex information.

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Transistors are combined to create logic[br]gates, which still do very simple stuff.

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For example, an AND gate sends an output[br]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[br]form meaningful modules,

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say, for adding two numbers.

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Once you can add, you can also multiply,[br]and once you can multiply,

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you can basically do anything.

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Since all basic operations are literally[br]simpler than first-grade math,

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you can imagine a computer as[br]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[br]anything, from astrophysics to Zelda.

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However, with parts[br]getting tinier and tinier,

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quantum physics are making things tricky.

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In a nutshell, a transistor[br]is just an electric switch.

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Electricity is electrons moving[br]from one place to another,

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so a switch is a passage that can block[br]electrons from moving in one direction.

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Today, a typical scale[br]for transistors is 14 nm,

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which is about 8 times less[br]than the HIV virus’s diameter

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and 500 times smaller[br]than a red blood cell’s.

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As transistors are shrinking[br]to the size of only a few atoms,

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electrons may just transfer themselves to[br]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[br]works quite differently from

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the predictable ways we’re used to,

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and traditional computers[br]just stop making sense.

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We are approaching a real physical[br]barrier for our technological progress.

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To solve this problem,[br]scientists are trying to

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use these unusual quantum[br]properties to their advantage

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by building quantum computers.

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In normal computers, bits[br]are the smallest units of information.

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Quantum computers use qubits, which[br]can also be set to one of two values.

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A qubit can be any[br]two-level quantum system,

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such as a spin in a magnetic field[br]or a single photon.

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Zero and one are this[br]system’s possible states,

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like the photon’s horizontal[br]or vertical polarization.

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In the quantum world, the qubit[br]doesn’t have to be in just one of those;

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it can be in any proportions[br]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,[br]by sending the photon through a filter,

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it has to decide to be either[br]vertically or horizontally polarized.

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So, as long as it’s unobserved, the qubit[br]is in a superposition of probabilities

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for zero and one, and you can’t[br]predict which it will be.

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But the instant you measure it, it[br]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[br]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,[br]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[br]16 combinations at once!

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This number grows exponentially[br]with each extra qubit.

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20 of them can already store[br]a million values in parallel.

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A really weird an unintuitive[br]property qubits can have

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is entanglement, a close connection that[br]makes each of the qubits

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react to a change in the other’s[br]state instantaneously,

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no matter how far they are apart.

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This means that when measuring[br]just one entangled qubit,

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you can directly deduce properties of[br]its partners without having to look.

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Qubit manipulation[br]is a mind-bender as well.

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A normal logic gate gets[br]a simple set of inputs

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and produces one definite output.

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A quantum gate manipulates[br]an input of superpositions,

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rotates probabilities, and produces[br]another superposition as its output.

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So a quantum computer sets up some qubits,[br]applies quantum gates to entangle them

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and manipulate probabilities,[br]then finally measures the outcome,

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collapsing superpositions to an[br]actual sequence of zeros and ones.

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What this means is that you[br]get the entire lot of calculations

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that are possible with your setup[br]all done at the same time.

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Ultimately, you can only[br]measure one of the results,

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and it will only probably[br]be the one you want,

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so you may have to[br]double-check and try again.

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But by cleverly exploiting[br]superposition and entanglement,

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this can be exponentially more efficient

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than would ever be possible[br]on a normal computer.

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So, while quantum computers will probably[br]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[br]to test every single one of its entries.

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Quantum algorithms need only[br]the square root of that time,

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which for large databases[br]is a huge difference.

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The most famous use of quantum[br]computers is ruining IT security.

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Right now, your browsing,[br]email, and banking data

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is being kept secure by an encryption[br]system in which you give everyone

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a public key to encode[br]messages only you can decode.

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The problem is that this[br]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[br]on any normal computer

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would literally take[br]years of trial and error.

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But a quantum computer[br]with exponential speedup

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could do it in a breeze.

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Another really exciting[br]new use is simulations.

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Simulations of the quantum world[br]are very intense on resources,

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and even for bigger structures,[br]such as molecules,

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they often lack accuracy.

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So why not simulate quantum physics[br]with actual quantum physics?

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Quantum simulations could provide[br]new insights on proteins

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that might revolutionize medicine.

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Right now we don’t know[br]if quantum computers will be

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just a very specialized tool[br]or a big revolution for humanity.

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We have no idea where[br]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[br]the Australian Academy of Science,

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which promotes and[br]supports excellence in science.

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Learn more about this topic[br]and others like it

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at .

0:06:58.911,0:07:01.917
It was a blast to work with them,[br]so go check out their site!

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