dark mode light mode Search Menu

What is Quantum Computing?

Cianan O'Dowd on Flickr

For the past few decades, scientists have been slowly working on a new kind of computer, one not built on simple zeros and ones but on something very different, something stranger: a kind of computer that operates on chance not certainty. These are quantum computers.

Quantum computers are the source of a lot of excitement and misunderstanding, so in this article I want to introduce a bit about what they are, what they are not, and what they might be able to do.

The simplest way to put it is that normal computers perform operations on data that have simple, definite values. If we have the number five, then we have the number of five. I can add three and five together and definitely get eight. All of this data is built out of bits, values that are either 0 or 1.

Quantum computers, on the other hand, are built on something a lot weirder than a bit: the quantum bit, qbit for short. The data stored in the qbit determines the chance you get a zero or one when you ask for it out of the bit.

To explain that further, I’m going to need to take an aside into quantum mechanics—the science of how objects move and behave at very, very tiny scales. While in our everyday lives we’re used to things moving in straight lines from here to there and moving through every point in between, things start acting differently at the scale of atoms or smaller.

Quantum mechanics tells us that the tiny building blocks of atoms are particles, very tiny objects, but their movement and behavior is described by waves. When I say waves I mean like sound waves or even ripples of water: shapes in space and time. These waves can be used to calculate the probability of where a particle will be, how fast it will be moving, things like that. And this probability, this chance, is real in the sense that if you were to test multiple particles that all had the same “wave shape” you’d get different answers like someone is rolling dice in the background. And these particles don’t move around simply, they jump around between places in accordance with the likelihood they’ll be found there.

That comparison to sound waves is actually kinda useful because the same way you can have noise canceling headphones that generate one set of waves to interfere with other waves, you can have these probability waves interfere with each other. The most famous example of this is the double slit experiment which you can read about in a companion piece in this issue.

So back to quantum computers: we’ve described that the qbits contain probability waves that describe the chance you get a zero or one as a result. This is much more complicated, richer, data than just a simple bit but a quantum computer can perform arithmetic and logical operations on these probability waves just as simply as a normal computer acts on numbers. This allows for some pretty cool things, where operations on qbits can get a lot more calculation done in a single step by ruling out wrong answers at the same time as working on possible right answers. This goes back to that whole wave interference thing. Good quantum algorithms come with their own noise canceling headphones: they cancel out wrong answers and amplify right ones.

What are good quantum algorithms? What kinds of things can quantum computers do? The short answer is that we’re not sure because we haven’t been studying them long enough. The long answer is that we know they can do certain things faster, like help you break the public-key encryption that practically every site on the internet uses, and that’s enough to make people want to study them more. We do know that in theory quantum computers can’t do anything magical that an ordinary computer can’t but they can potentially do things so much faster that something that would take years for a computer could take only minutes for a quantum computer.

The main obstacle right now is actually building one that’s useful. We can construct some small computers that have a few dozen qbits but even those are unstable and only usable for short periods at a time.

Even with those caveats, quantum computers are exciting. It’s this huge unknown world of new techniques, kinds of hardware, and ways of writing programs that the next few decades is going to explore. Maybe you’ll be part of it!

Learn More

A programming language for quantum computers


Silq programming language


Quantum Programming


Quantum Computing video


Quantum Computers


15 Things to know about Quantum Computing


Mind-boggling facts about quantum computers


Quantum Computing


What is a Qubit


Quantum Computer Facts for Kids


Quantum activity pack


Quantum Computer takes huge step