Question: have you invented anything

Nathan Langford answered on 25 Jun 2012:

Hi brendan999,

Yes, I did come up with something which was kind of like a proper invention… When I was working in Vienna, my colleagues and I invented a new way to build a “quantum computer” using light. So what is that? Well, the easiest way to think about quantum physics is that it is the theory that describes the behaviour of things that are either very small, or very cold. So a quantum computer is a computer that is built using “quantum particles”, that behave like quantum physics expects them to. It turns out that there are some special tasks that are incredibly slow to solve with a normal computer, but that could be solved very quickly on a quantum computer. They could also be used to simulate the behaviour of DNA or photosynthesis and make unbreakable cryptocodes. If you’d like to read a bit more about why this might be useful or interesting, I’ll write a bit at the bottom of this post, or, if you’re brave, you can read a web article we wrote about our work for upper high school and undergraduate uni students:

http://www.2physics.com/2011/11/new-scheme-for-photonic-quantum.html

As an experimental physicist, when we discover new things, we also tend to try and think about possible ways of using them to do something interesting – in other words, an invention. So physicists are always trying to make inventions.

The difficulty about inventing things as a physicist, is that there is often quite a big separation between an idea based on new physics principles or knowledge and something that you can actually build. In fact, most physics research is carried out in answer to the question, “how does this work?” And while, as experimental researchers, we then usually try to think about how that new information might be useful, it’s normally a matter of possibilities, rather than something you can write on a “to do” list. You might hear this referred to as “blue sky” research.

A good example is optical fibres. The idea of “total internal reflection” has probably been around as long as something called Snell’s Law, which was discovered in 1621 (according to my trusty undergraduate physics textbook). But optical fibres, which rely only on total internal reflection to work, were not invented until the 1950s and now they’re used everywhere. So often these ideas wait around for the technology to reach the right place before they can really take off.

Sometimes, even if you have a “thing” and not just an idea, it still takes a long time to take off. For example, the first laser was invented *and built* in 1960, but everyone thought it was just a toy, with no practical usefulness. Now, just 50 or so years later, like optical fibres, they’re everywhere. (There’s some more information about lasers in my profile.)

I think quantum computers might be just as revolutionary as the laser when someone eventually manages to put everything together in just the right way.

Have fun!
Nathan.

What is a quantum computer?

As I mentioned above, quantum physics works well when describing things that are very small or very cold. Now, by very small, I don’t mean mosquitos or microbes, but rather molecules, atoms and subatomic particles like electrons and protons. By very cold, I mean 100s or 1000s of times colder than space – just a small fraction of a degree above absolute zero. These are pretty good rules of thumb, except in very special conditions. Otherwise, the high temperatures or sheer numbers of particles introduce randomness, which stuffs up the quantumness. Even when everything is behaving perfectly, quantum physics can still be very complex, so it’s often very hard to do calculations or make predictions about objects made from more than just a few particles. That’s one of the reasons why a quantum computer would be so interesting – we could use a quantum computer to predict the behaviour of complex quantum systems much faster than we could do even on the largest modern computers.

But although we know some of the things we could do if we had a quantum computer, no one has built one yet! It turns out that it’s really hard to do and the reason why comes back to what I said above, that quantum physics generally only describes things that are really small or really cold – in fact, preferably both. And, unfortunately, in order to do anything interesting, we basically need to have a quantum computer that is big enough to break at least the first of these rules. Even for the simplest things, we would probably need a computer built of 100s of particles, which is much bigger than anything anyone has yet managed.

One physical system people are looking at using to build a quantum computer is laser light, which has some tantalisingly nice properties. For example, if you look at very small packets of light, called photons, because they have no mass and no charge, they can behave “quantum-ly” even at normal room temperatures. This is because the photons don’t interact very strongly with the environment around them and don’t get messed up by it. But this also creates the biggest problem for using photons – it is very difficult to get them talking even to each other! My invention was to come up with a new way to make the photons interact with each other which might solve all the barriers for building a quantum computer that’s big enough to be useful. There’s an awful long way to go yet, however, and we don’t yet know whether it will work – but that’s why it’s exciting!