Week 1: the first layer of the quantum onion

Last week I promised to do some learning in public, to spend at least a few weeks attempting to get to grips with a subject I know little about: quantum computing.

The rules were that in the first week, I would only look at articles from the press, not written by specialists in the field, partly to introduce myself to the subject, but also to get a feel for how much a curious layperson can be expected to understand from such articles. In subsequent weeks, I will go deeper, reading specialist texts and, if possible, getting the advice of experts.

So, to follow my self-imposed rule, I started this week by opening up my browser, typing in ‘quantum computing’, selecting ‘news’, and reading the first half dozen or so articles.

The first article was about nations investing in quantum computing. Straight away, I learnt something new, but also had new questions.

First, the article said that quantum computers need to be cooled to near absolute zero. Why is this? And how near to absolute zero to they have to be? (I know that eliminating those last few fractions of a degree are extraordinarily difficult, and result in some strange quantum phenomena. Do quantum computers have to be that cold?)

Second, the article mentioned qubits, explaining that they are quantum bits, and that they are a complex mix of zeroes and ones simultaneously. I’d go on to encounter several similar descriptions of qubits, saying variously that they are zero and one at the same time, that they are a mixture of zero and one, and that they are on a continuum from zero to one. What does this actually means? And how do you do computing with such a bit?

Third, the article mentioned that quantum computers are particularly well suited to simulate and model the behaviour of complex molecules, and can therefore help with research into vaccines and material science. Again, I would go on to encounter this claim in several articles. Why should this be the case? Some of the articles implied that it is because traditional digital computers are not good at modelling uncertain quantum behaviour. Does this mean that quantum computers are operating in some sort of analogue fashion when modelling molecules? Does the quantum behaviour of the computer mimic the quantum behaviour of the molecule?

Fourth, the article also asserted that quantum computers are particularly good for AI, because they have some sort of similarity to the brain’s neural network. I must admit that I was sceptical: I understand a bit about how neural networks are created in normal digital computers, and struggle to see what would make a quantum computer better at this job. But it would not be the only time I would encounter the claim that quantum computers are good at AI.

Finally, the article gave me some practical and commercial facts: that the fastest quantum computer today is made by IBM and has 127 qubits, and that each quantum computer costs about $100 million. I suspect that facts like these - how powerful a quantum computer is, how much it costs and who is in the lead - will change continuously, and will only ever be accurate at the time of going to press, if then.

Most of the articles I read after that first one reinforced these points, and only gave me a few more facts. A bit like other complex topics, reading articles on quantum computing gets repetitive quite quickly. I did learn, though, that the reason that quantum computers look so strange is due to the need for extreme cooling: slightly disappointingly, the weird pipes and cylinders aren’t doing any of the processing. They’re just transferring heat. This means that, intriguingly, I have no idea what the physical processor of a quantum computer looks like.

I also learnt, though, that I should expect these processors to look different from each other: it sounds as if different computers are working with different fundamental properties at the quantum level. For example, one article mentioned ‘resonators’, each which is a three dimensional superconducting cavity made of aluminium. I know what all of those words mean individually: right now, I have little idea of their significance when you put them together.

And I learnt that a lot of the advances in quantum computing today have to do with error correction. However those three dimensional superconducting cavities or their alternatives work, they seem to be very delicate as well as very cold. So, the question of how you actually read the value of a qubit seems even harder to answer.

Finally, I encountered one more common description of why quantum computers will change the world (most of the articles were confident that they would change the world): that they compute all paths through a problem simultaneously. The standard analogy was that of someone trying every route through a maze at the same time, solving it instantly. But I still don’t know how this works.

So, I’m leaving my foray into the articles on quantum computing slightly better informed than I was, but with more questions than when I started. I also came away with the feeling that, as I expected, this field is both hard to write about and hard to read about in lay terms. There is something about the term ‘quantum’ which creates a mental barrier: an expectation in the reader that they won’t be able to understand, and an expectation in the writer that they won’t be able to fully explain. In the next week or so, I’ll go a bit deeper and try to clamber over this barrier.

(Views in this article are my own.)