Quantum from Scratch · Episode 9 of 19

Gate-based vs annealing

Gate-Based vs Annealing Quantum Computers Explained Simply

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What I say in the video

You can't just run Python on a quantum computer.

You write your code on a normal machine. Software turns it into steps the chip can follow. Each step is called a gate. That's a gate-based machine. Whatever steps you write, it follows — for as long as the qubits hold.

Another kind of quantum computer won't take steps at all.

You turn your problem into a score — low is good, high is bad — and set that onto the qubits.

The machine settles on the lowest score it can find.

That's an annealer.

Both take your problem. Only one follows your steps.

Next episode, the last one: what quantum can actually do.

In plain words

Can you run code on a quantum computer? Not the way you'd expect — and not on every kind of quantum computer.

This explains the difference between gate-based quantum computers and quantum annealers, from scratch, in under a minute, with no maths.

What the video covers:

Why your Python doesn't run directly on a quantum chip
What actually happens to your code before the machine sees it
What a "gate" is, in one sentence
Why a gate-based machine only follows your steps for as long as the qubits last
The other kind of quantum computer, which takes no instructions at all
How you program a machine by handing it a problem instead of a procedure
Why both are genuinely quantum, and what really separates them

What I simplified

The bit that didn't fit in the reel, and it's the most interesting part: HOW does an annealer get out of a bad answer? If it only ever slid downhill it would get stuck in the first dip it found — and that would just be an ordinary computer doing ordinary search. The quantum part is that it can pass THROUGH a barrier instead of going over it. That's called tunnelling, and it's the whole reason the machine is quantum rather than just clever. Two honest caveats while I'm here. It finds a very low score, not always THE lowest — annealing gives you a good answer, not a guaranteed perfect one. And "gate-based" covers machines built from very different stuff: supercold chips, single trapped atoms, beams of light. What they're MADE of is a different question from what they're built to DO. Next: the last episode. What quantum can actually do.

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