In quantum mechanics, an electron can be spinning clockwise and anticlockwise at the same time, and a proton can be in two places at once. It sounds like science fiction, but that’s only because the crazy quantum nature of our universe, it hides itself from us. And it stayed hidden from us until the 20th century.
But now that we’ve seen it, the whole world is in an arms race to try to build a quantum computer — a computer that can harness the power of this weird and wacky quantum behavior.
These things are so revolutionary and so powerful that they’ll make today’s fastest supercomputer look useless in comparison. In fact, for certain problems that are of great interest to us, today’s fastest supercomputer is closer to an abacus than to a quantum computer. That’s right, I’m talking about those little wooden things with the beads.
Quantum computers can simulate chemical and biological processes that are far beyond the reach of our classical computers. And as such, they promise to help us solve some of our planet’s biggest problems. They’re going to help us combat global hunger; to tackle climate change; to find cures for diseases and pandemics for which we’ve so far been unsuccessful; to create superhuman artificial intelligence; and perhaps even more important than all of those things, they’re going to help us understand the very nature of our universe.
But with this incredible potential comes an incredible risk. Remember those big numbers I talked about earlier? I’m not talking about 851. In fact, if anyone in here has been distracted trying to find those factors, I’m going to put you out of your misery and tell you that it’s 23 times 37. I’m talking about the much bigger number that followed it.
While today’s fastest supercomputer couldn’t find those factors in the life age of the universe, a quantum computer could easily factorize numbers way, way bigger than that one.
Quantum computers will break all of the encryption currently used to protect you and I from hackers. And they’ll do it easily.
Let me put it this way: if quantum computing was a spear, then modern encryption, the same unbreakable system that’s protected us for decades, it would be like a shield made of tissue paper. Anyone with access to a quantum computer will have the master key to unlock anything they like in our digital world.
They could steal money from banks and control economies. They could power off hospitals or launch nukes. Or they could just sit back and watch all of us on our webcams without any of us knowing that this is happening.
Now, the fundamental unit of information on all of the computers we’re used to, like this one, it’s called a “bit.” A single bit can be one of two states: it can be a zero or it can be a one.
When I FaceTime my mum from the other side of the world — and she’s going to kill me for having this slide — we’re actually just sending each other long sequences of zeroes and ones that bounce from computer to computer, from satellite to satellite, transmitting our data at a rapid pace.
Bits are certainly very useful. In fact, anything we currently do with technology is indebted to the usefulness of bits. But we’re starting to realize that bits are really poor at simulating complex molecules and particles. And this is because, in some sense, subatomic processes can be doing two or more opposing things at the same time as they follow these bizarre rules of quantum mechanics.
So, late last century, some really brainy physicists had this ingenious idea: to instead build computers that are founded on the principles of quantum mechanics.
Now, the fundamental unit of information of a quantum computer, it’s called a “qubit.” It stands for “quantum bit.” Instead of having just two states, like zero or one, a qubit can be an infinite number of states. And this corresponds to it being some combination of both zero and one at the same time, a phenomenon that we call “superposition.”
And when we have two qubits in superposition, we’re actually working across all four combinations of zero-zero, zero-one, one-zero and one-one. With three qubits, we’re working in superposition across eight combinations, and so on.
Each time we add a single qubit, we double the number of combinations that we can work with in superposition at the same time. And so when we scale up to work with many qubits, we can work with an exponential number of combinations at the same time. And this just hints at where the power of quantum computing is coming from.
Now, in modern encryption, our secret keys, like the two factors of that larger number, they’re just long sequences of zeroes and ones. To find them, a classical computer must go through every single combination, one after the other, until it finds the one that works and breaks our encryption.
But on a quantum computer, with enough qubits in superposition, information can be extracted from all combinations at the same time. In very few steps, a quantum computer can brush aside all of the incorrect combinations, home in on the correct one and then unlock our treasured secrets.
Now, at the crazy quantum level, something truly incredible is happening here. The conventional wisdom held by many leading physicists — and you’ve got to stay with me on this one — is that each combination is actually examined by its very own quantum computer inside its very own parallel universe.