00:00For most of our history, human technology consisted of our brains, fire, and sharp sticks.
00:06While fire and sharp sticks became power plants and nuclear weapons,
00:10the biggest upgrade has happened to our brains.
00:13Since the 1960s, the power of our brain machines has kept growing exponentially,
00:18allowing computers to get smaller and more powerful at the same time.
00:22But this process is about to meet its physical limits.
00:26Computer parts are approaching the size of an atom.
00:29To understand why this is a problem, we have to clear up some basics.
00:33A computer is made up of very simple components doing very simple things,
00:38representing data, the means of processing it, and control mechanisms.
00:43Computer chips contain modules, which contain logic gates, which contain transistors.
00:48A transistor is the simplest form of a data processor in computers,
00:52basically a switch that can either block or open the way for information coming through.
00:58This information is made up of bits, which can be set to either 0 or 1.
01:03Combinations of several bits are used to represent more complex information.
01:07Transistors are combined to create logic gates, which still do very simple stuff.
01:12For example, an AND gate sends an output of 1 if all of its inputs are 1,
01:17and an output of 0 otherwise.
01:19Combinations of logic gates finally form meaningful modules, say, for adding two numbers.
01:25Once you can add, you can also multiply, and once you can multiply, you can basically do anything.
01:31Since all basic operations are literally simpler than first-grade math,
01:35you can imagine a computer as a group of seven-year-olds answering really basic math questions.
01:40A large enough bunch of them could compute anything from astrophysics to Zelda.
01:45However, with parts getting tinier and tinier, quantum physics are making things tricky.
01:50In a nutshell, a transistor is just an electric switch.
01:54Electricity is electrons moving from one place to another,
01:57so a switch is a passage that can block electrons from moving in one direction.
02:02Today, a typical scale for transistors is 14 nanometers,
02:06which is about eight times less than the HIV virus's diameter,
02:09and 500 times smaller than a red blood cell's.
02:13As transistors are shrinking to the size of only a few atoms,
02:16electrons may just transfer themselves to the other side of a blocked passage
02:20via a process called quantum tunneling.
02:22In the quantum realm, physics works quite differently from the predictable ways we're used to,
02:27and traditional computers just stop making sense.
02:31We are approaching a real physical barrier for our technological progress.
02:35To solve this problem, scientists are trying to use these unusual quantum properties to their advantage
02:41by building quantum computers.
02:43In normal computers, bits are the smallest units of information.
02:47Quantum computers use qubits, which can also be set to one of two values.
02:52A qubit can be any two-level quantum system, such as a spin in a magnetic field or a single photon.
02:58Zero and one are this system's possible states, like the photon's horizontal or vertical polarization.
03:05In the quantum world, the qubit doesn't have to be in just one of those,
03:08it can be in any proportions of both states at once.
03:12This is called superposition.
03:14But as soon as you test its value, say by sending the photon through a filter,
03:18it has to decide to be either vertically or horizontally polarized.
03:23So as long as it's unobserved, the qubit is in a superposition of probabilities for zero and one,
03:29and you can't predict which it will be.
03:31But the instant you measure it, it collapses into one of the definite states.
03:36Superposition is a game-changer.
03:39Four classical bits can be in one of two to the power of four different configurations at a time.
03:44That's 16 possible combinations, out of which you can use just one.
03:49Four qubits in superposition, however, can be in all of those 16 combinations at once.
03:55This number grows exponentially with each extra qubit.
03:5820 of them can already store a million values in parallel.
04:02A really weird and unintuitive property qubits can have is entanglement,
04:07a close connection that makes each of the qubits react to a change in the other's state instantaneously,
04:12no matter how far they are apart.
04:14This means that when measuring just one entangled qubit,
04:17you can directly deduce properties of its partners without having to look.
04:22Qubit manipulation is a mind-bender as well.
04:25A normal logic gate gets a simple set of inputs and produces one definite output.
04:30A quantum gate manipulates an input of superpositions,
04:34rotates probabilities, and produces another superposition as its output.
04:39So a quantum computer sets up some qubits,
04:42applies quantum gates to entangle them and manipulate probabilities,
04:45and finally measures the outcome, collapsing superpositions to an actual sequence of zeros and ones.
04:52What this means is that you get the entire lot of calculations
04:55that are possible with your setup all done at the same time.
04:58Ultimately, you can only measure one of the results,
05:01and it will only probably be the one you want,
05:03so you may have to double-check and try again.
05:06But by cleverly exploiting superposition and entanglement,
05:10this can be exponentially more efficient than would ever be possible on a normal computer.
05:15So while quantum computers will probably not replace our home computers,
05:19in some areas they are vastly superior.
05:22One of them is database searching.
05:24To find something in a database,
05:26a normal computer may have to test every single one of its entries.
05:30Quantum algorithms need only the square root of that time,
05:33which for large databases is a huge difference.
05:36The most famous use of quantum computers is ruining IT security.
05:41Right now, your browsing, email, and banking data
05:44is being kept secure by an encryption system
05:46in which you give everyone a public key to encode messages only you can decode.
05:51The problem is that this public key can actually be used to calculate your secret private key.
05:56Luckily, doing the necessary math on any normal computer
05:59would literally take years of trial and error.
06:02But a quantum computer with exponential speedup could do it in a breeze.
06:06Another really exciting new use is simulations.
06:09Simulations of the quantum world are very intense on resources,
06:13and even for bigger structures, such as molecules, they often lack accuracy.
06:18So why not simulate quantum physics with actual quantum physics?
06:23Quantum simulations could provide new insights on proteins that might revolutionize medicine.
06:28Right now, we don't know if quantum computers will be just a very specialized tool
06:32or a big revolution for humanity.
06:35We have no idea where the limits of technology are,
06:38and there's only one way to find out.
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