QPU, Quantum Accelerator and Quantum Computing
The connotations of your terminology matter to how your work is perceived.
Moore’s law is the observation that every two years or so, the number of transistors doubles. This lead some people to realize that at some point, all computers would need to be quantum computers. Unfortunately this is not the case. See my recent post on loops to learn why.
These early quantum computing theorists were not dumb, they saw the issues with no cloning it seemed to be just an odd suggestion of the universe, surely we could exploit something to allow a quantum computer to act just like a classical computer…. but better. And so, some of these earlier works came with the assumption that classical computers would evolve into quantum computers and the research done on truly quantum computers would feed back in, but transistors would one day take over.
As I said before, this is sadly not the case. However the misconception is still around. I’m very pleased that it’s lost momentum, even since I first started writing about the subject the situation has improved. I’m here today to further attack a waining position.
And quite honestly, I feel justified in doing it. Despite the insistence of physicists and engineers deep in the weeds of building the cutting edge systems, those of us who care to share the work in a popular manner do still hear people wondering about when quantum computing will replace classical computers.
The quick answer
Historically (and I’ll post on this later) “computer” was a job title. Same as “programmer” or “engineer”, but with a different skillset and pay grade. Kind of like Data scientist and ML engineer today. By this definition, my TI-84 from college is a computer. A four function calculator is also a computer. The language has shifted. And it continues.
Today, we see calculators (some more powerful than what put us on the moon) as a different class then a computer.
Quantum Computers
When I was younger computers had a tendency to be separated from the screens and other input/output devices. I remember having a large box with fans sitting under a desk, and a screen, keyboard and mouse sitting on that desk. But now, most computers I see are laptops. one unit, screen folds down nicely to the keyboard for transport. You can’t detach it.
Oh but it gets worse, the device I’m writing this on is also a computer. A phone. A slab of glass and plastic. Sleek, single unit. Atomic one might say.
I think we can fall into the trap of seeing computers this way. Atomic.
Quantum computers are different beasts all together. They are definitely made up of parts, a classical server, control and readout structures and then the actual quantum processor. It’s not atomic, each part is necessary. The server makes it usable, the control and readout translate between classical and quantum, while the actual calculations are done on the quantum processor.
Quantum Processor/QPU
While technically this is the part that’s actually quantum, I really like using these terms. The reason is simple, especially with QPU I’m bringing in the idea of a GPU into the picture.
You have a CPU and GPU, I suspect that a lot of new computers (both ThinkPads I’ve gotten recently for example) are getting NPUs, and I’m sure developers are at least aware of TPUs and other accelerators like them. The QPU terminology brings this sort of thing to mind.
I’m not saying that a quantum computer is like a C,G or NPU, something that you can have hidden away in your laptop. Think of it more like a TPU, it exists on a server somewhere and if you need it you can access it…. with the right type of cloud credits.
Quantum Accelerator
In the same vein as QPU, but a little more insulated from the idea of having it in your laptop. Basically it makes stuff faster…. somehow. Probably not by sitting on your lap.
While QPU can feel like something that slots into a server rack or port on a computer, this feels a little more nebulous and other. Something a little more complicated to hold on to.
Obviously this is not the technical terminology, rather it’s an attempt at providing a framework for the ways I see each term used. Technical and common don’t always align. It just depends on the field. There are some fields where the CPU could very well be the computer, the rest is just supporting hardware. The same is true of QPUs, it’s just a question of context.