New quantum computing paradigm could make all the difference
Image: IBM
Something is brewing in quantum computing, people, and this could be a total game changer.
It’s hard to evaluate the promise of quantum computing because there are so many people who have a reason to exaggerate their research, so much so that sometimes I’m not sure whether they’re joking or not. For example: “At D-wave, my title is the vice-president of quantum technology evangelism.”
But I think there’s really something going on. I have in the past years told you a few times that photonic quantum computing is hot, hot, hot. Just a few weeks ago I mentioned that the photonic computing company PsiQuantum has attracted substantial new funding and put forward a design plan for a scalable quantum computer that could bring them up to a million qubits very quickly.
They have partnered up with the microchip manufacturer GlobalFoundries to get the job done, and just last week I read that they’ve acquired factory ground near Chicago. These people are clearly very sure that they’ve got it sorted out.
The interesting thing that I want to talk about today is the reason for why this is happening and what that may be doing to the rest of quantum computing.
Photonic quantum computing, as the name says, works with photons. But you see the issue with photons is that there’s no easy way to entangle them once you have created them. You can create them entangled, and physicists do that all the time. But changing the entanglement later is difficult. This is because photons don’t interact with each other.
Some groups are trying to get this done with non-linear in-medium effects, which is very interesting, but it’s complicated. This is why PsiQuantum is using a different approach.
The standard approach is called gate-based and it’s very similar to how a conventional computer works. A logical gate is the computer entry point for Bill Gates. Just checking if you’re listening.
A gate is the part of a computer that performs the logical operations of a computation. You start with your qubits in a default state, and then you apply operations to them that move the entanglement around.
At the very end you make a measurement, and where you find your qubits that gives you the answer, or at least that’s the idea. The problem is that how well this works depends a lot on how good the gates are.
But because that’s so difficult to do with photons anyway, the photonic people do it differently. They start with a big state of entangled photons, and then use those as the initial state and then just do measurements. It’s called measurement-based quantum computing.
This has a couple of advantages, most importantly: You don’t have to worry about how good your gates are! It’s also easier to make fast measurements parallel to each other than it is to do gate operations which gives a speed advantage. And there are some error correction protocols which can be used on the measurement based approach that don’t work on the gate based approach.
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