How Our Tech Grew, and Where It’s Hitting a Wall#

Think about our history for a moment. For most of it, human technology was pretty basic: just our clever brains, fire, and pointy sticks. Fire and those sticks eventually led to big things like power plants and nuclear weapons. But the really huge change happened with our brains – specifically, machines built by our brains.

Since the 1960s, the power of our computing machines has shot up like crazy, getting smaller and more powerful all the time. But here’s the thing: this growth is bumping up against physical limits now. The tiny parts inside computers are getting close to the size of single atoms. To get why this is a problem, we need to cover some basics first.

The Building Blocks of Normal Computers#

Let’s break down how a regular computer works in a simple way. It’s basically made of very simple pieces doing very simple jobs:

• Handling data
• Processing that data
• Controlling everything

Inside computer chips, you find:

• Modules
• Which contain Logic Gates
• Which contain Transistors

A transistor is the simplest bit of data processing. Think of it as a simple switch that can either block information from passing through or let it through.

Information in computers is stored using bits. A bit can be set to one of two values: 0 or 1. You combine several bits to represent more complicated stuff.

Transistors are put together to make logic gates. These gates still do really simple things. For example, an AND Gate only sends out a ‘1’ if all of its inputs are ‘1’. Otherwise, it sends out a ‘0’.

Combine logic gates, and you get meaningful modules, like one that adds two numbers. Once you can add, you can multiply. And once you can multiply, you can pretty much do anything!

Imagine a computer as a huge group of 7-year-olds answering simple math questions. A big enough group of them could figure out anything, from astrophysics problems to playing Zelda.

The Problem with Getting Too Small: Quantum Weirdness#

Here’s where things get tricky as parts shrink. Remember, a transistor is just an electric switch. Electricity is just electrons moving. So, a switch is like a blocked path stopping electrons from going one way.

Today, transistors are incredibly small, often around 14 nanometers. To give you perspective:

• That’s about 8 times smaller than the diameter of the HIV virus.
• And 500 times smaller than a red blood cell.

As transistors keep shrinking down to the size of just a few atoms, a bizarre thing from the quantum world starts happening. Electrons might just jump through the blocked path to the other side. This is called Quantum Tunneling.

In the quantum realm, physics doesn’t work the way we expect or can easily predict. When parts get this small, traditional computers stop making sense because of these weird effects. This is a real physical barrier limiting how much further we can shrink things and make computers faster in the traditional way.

The Solution? Go Quantum!#

To get past this barrier, scientists are trying to turn these unusual quantum properties into an advantage. How? By building quantum computers.

Classical Bits vs. Qubits

• In normal computers, the smallest piece of information is a bit (either 0 or 1).
• Quantum computers use qubits. They can also represent two values. A qubit can be any two-level quantum system. Examples include:
  • A spin in a magnetic field.
  • A single photon (light particle).
• The ‘0’ and ‘1’ represent the system’s possible states (like a photon being horizontally or vertically polarized).

Superposition: Being Both at Once

In the quantum world, a qubit doesn’t have to be just one of those states (0 or 1). It can be in a mix of both states at the same time, in varying amounts. This is called superposition.

But there’s a catch! As soon as you try to check its value (like sending a photon through a filter), it has to ‘decide’ and collapse into just one state (either vertical or horizontal polarization).

So, until you measure it, a qubit is in a superposition of probabilities for being 0 or 1. You can’t know which it will be for sure. But the moment you measure, it snaps into one definite state.

Why Superposition is a Game Changer

Let’s look at the difference with just a few bits:

• Four Classical Bits: Can be in one configuration at a time out of 2^4 = 16 possible combinations. You can only use one of these 16 combinations at any given moment.
• Four Qubits in Superposition: Can effectively be in all 16 combinations at once.

This power grows incredibly fast. Just twenty qubits in superposition can already store a million values in parallel (meaning, at the same time).

Entanglement: Spooky Connections

Another really weird and mind-bending property qubits can have is Entanglement. This is a deep connection between qubits. If you change the state of one entangled qubit, the others react instantly, no matter how far apart they are.

This is useful because if you measure just one entangled qubit, you can figure out things about its partners without even looking at them directly.

Manipulating Qubits with Quantum Gates

• A normal logic gate takes simple inputs (0s and 1s) and gives one definite output.
• A quantum gate works on an input that might be in a superposition. It doesn’t give a definite 0 or 1 output right away. Instead, it manipulates the probabilities of the superposition and produces another superposition as its output.

How a Quantum Computer Works (Simplified)

1. You set up some qubits.
2. You apply quantum gates to:
   • Entangle the qubits (create those spooky connections).
   • Manipulate the probabilities held within their superpositions.
3. Finally, you measure the outcome. This forces the superpositions to collapse into an actual sequence of 0s and 1s, which is your result.

What this means is that potentially, you get all the possible calculations for your setup done simultaneously! You only measure one result at the end, and it might only be the one you wanted probably. So, you might need to check and run it again. But by being smart about using superposition and entanglement, this process can be vastly, exponentially more efficient for certain tasks than any normal computer could ever be.

Where Quantum Computers Will Shine (and Where They Won’t)#

Quantum computers likely won’t replace your home computer or phone. They are specialized tools. But in some specific areas, they are way, way better than classical computers.

1. Searching Databases:

• To find something in a big database, a normal computer might have to check every single item one by one.
• Quantum computer algorithms can do this much faster, in a time proportional to the square root of the number of items. For huge databases, this is a massive time save.

2. Breaking IT Security:

• This is one of the most talked-about uses. Right now, things like your browsing, email, and banking data are kept safe by encryption. This system often uses a public key (which anyone can have to encode messages) and a secret private key (only you have, to decode them).
• The public key can technically be used to figure out your private key. But doing the math needed on any normal computer would take years of trial and error.
• A quantum computer, with its exponential speed-up for certain problems, could do this calculation in a flash. This means current encryption methods could become insecure.

3. Running Simulations:

• Simulating the quantum world (like how molecules interact) is incredibly demanding on normal computers. Even for relatively simple structures like molecules, these simulations often aren’t very accurate.
• So, why not use actual quantum physics to simulate quantum physics? Quantum simulations could unlock huge discoveries, for example, providing new insights into proteins. This could potentially revolutionize medicine.

Looking Ahead#

Right now, we don’t know for sure if quantum computers will remain a specialized tool for just a few tasks, or if they will bring about a massive revolution for humanity. We truly have no idea where the ultimate limits of technology lie. There’s only one way to find out: keep exploring and building!

Just so you know, this video was supported by the Australian Academy of Science. They’re all about promoting and helping out excellent science. You can learn more about quantum computing and other cool science stuff on their website: nova.org.au. It was really fun working with them, so definitely go check out their site!

Also, our videos are possible thanks to awesome people like you supporting us on patreon.com. If you want to help us out and join what we call the ‘Kurzgesagt bird army,’ check out our Patreon page!

(Big thanks to James Zhang for the original subtitles, Pietro Pasquero for revising them, and P0ck3tL1nt for corrections!)